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Exercise cuts heart disease risk in part by lowering stress, study finds.

Benefits nearly double for people with depression

MGH Communications

New research indicates that physical activity lowers cardiovascular disease risk in part by reducing stress-related signaling in the brain.

In the study, which was led by investigators at Massachusetts General Hospital and published in the  Journal of the American College of Cardiology , people with stress-related conditions such as depression experienced the most cardiovascular benefits from physical activity.

To assess the mechanisms underlying the psychological and cardiovascular disease benefits of physical activity, Ahmed Tawakol , an investigator and cardiologist in the Cardiovascular Imaging Research Center at Massachusetts General Hospital, and his colleagues analyzed medical records and other information of 50,359 participants from the Mass General Brigham Biobank who completed a physical activity survey.

A subset of 774 participants also underwent brain imaging tests and measurements of stress-related brain activity.

Over a median follow-up of 10 years, 12.9 percent of participants developed cardiovascular disease. Participants who met physical activity recommendations had a 23 percent lower risk of developing cardiovascular disease compared with those not meeting these recommendations.

Individuals with higher levels of physical activity also tended to have lower stress-related brain activity. Notably, reductions in stress-associated brain activity were driven by gains in function in the prefrontal cortex, a part of the brain involved in executive function (i.e., decision-making, impulse control) and is known to restrain stress centers of the brain. Analyses accounted for other lifestyle variables and risk factors for coronary disease.

Moreover, reductions in stress-related brain signaling partially accounted for physical activity’s cardiovascular benefit.

As an extension of this finding, the researchers found in a cohort of 50,359 participants that the cardiovascular benefit of exercise was substantially greater among participants who would be expected to have higher stress-related brain activity, such as those with pre-existing depression.

“Physical activity was roughly twice as effective in lowering cardiovascular disease risk among those with depression. Effects on the brain’s stress-related activity may explain this novel observation,” says Tawakol, senior author of the study.

“Prospective studies are needed to identify potential mediators and to prove causality. In the meantime, clinicians could convey to patients that physical activity may have important brain effects, which may impart greater cardiovascular benefits among individuals with stress-related syndromes such as depression.”

This work was supported by the National Institutes of Health.

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How Exercise Boosts the Brain and Improves Mental Health

New research is revealing how physical activity can reduce and even ward off depression, anxiety and other psychological ailments

Bob Holmes, Knowable

It’s hardly news that exercise is good for your physical health , and has long been extolled for mental health as well. But researchers are now making progress in understanding how, exactly, exercise may work its mental magic.

Exercise, they are learning, has profound effects on brain structure itself, and especially in regions most affected by depression and schizophrenia. It also provides other, more subtle benefits such as focus, a sense of accomplishment and sometimes social stimulation, all of which are therapeutic in their own right. And while more is generally better, even modest levels of physical activity, such as a daily walk, can pay big dividends for mental health.

“It’s a very potent intervention to be physically active,” says Anders Hovland, a clinical psychologist at the University of Bergen in Norway.

But that knowledge has barely begun to percolate into practice, says Joseph Firth, a mental health researcher at the University of Manchester in the UK. Just ask a hundred people receiving mental health care how many are getting exercise prescriptions as part of that care. “You wouldn’t find many,” Firth says.

Exercise — a tool against depression

Some of the strongest evidence for the mental benefits of exercise centers on depression. In 2016, Hovland and his colleagues searched the published literature and identified 23 clinical trials that tested the effectiveness of exercise in treating depression. Exercise was clearly effective and, in few studies, on par with antidepressant drugs, the researchers concluded.

And exercise offers several advantages. For one thing, antidepressant medications generally take several weeks or months to show their full effect. Exercise can improve mood almost immediately, making it a valuable supplement to frontline treatments such as drugs or therapy, notes Brett Gordon, an exercise psychology researcher at the Penn State College of Medicine. Plus, he says, exercise can counteract some of the unpleasant side effects of antidepressants, such as weight gain.

In addition, exercise has few of the negative side effects that are so common in drug therapies for depression and other disorders. “Many people who have mental health concerns are not enthusiastic about starting a medication for the rest of their lives, and are interested in pursuing other options. Exercise might be one of those options,” says Jacob Meyer, an exercise psychologist at Iowa State University.

There’s now emerging evidence that exercise also seems to help in treating or avoiding anxiety disorders , including post-traumatic stress disorder (PTSD), and possibly other serious psychotic conditions as well. “The more we do these studies, the more we see that exercise can be valuable,” says Firth.

There’s a flip side to this coin that’s especially relevant during the Covid-19 pandemic: If exercise stabilizes mental health, then anything that prevents people from working out is likely to destabilize it. To test this, Meyer and his colleagues surveyed more than 3,000 Americans about their activity before and during the pandemic. Those who became less active because of Covid reported more depression and poorer mental health , they found. (Ironically, those who had not exercised regularly pre-Covid didn’t report much change. “When you’re already at zero, where do you go?” says Meyer.)

But researchers are still figuring out exactly how muscular exertion acts on the brain to improve mental health. For most biomedical questions like this, the first stop is animal experiments, but they aren’t as useful in studies of mental health issues. “Psychological health is so uniquely human that it can be hard to make a good jump from animal models,” says Meyer.

Exercise and a healthy brain

Scientists have come up with a few ideas about how exercise enhances mental health , says Patrick J. Smith , a psychologist and biostatistician at Duke University Medical Center in North Carolina, who wrote about the subject in the 2021 Annual Review of Medicine with his Duke colleague Rhonda M. Merwin. It doesn’t seem to have much to do with cardiovascular fitness or muscular strength — the most obvious benefits of exercise — since how hard a person can work out is only weakly associated with their psychological health. Something else must be going on that’s more important than mere fitness, says Smith.

One likely possibility is that exercise buffs up the brain as well as the body. Physical exercise triggers the release of a protein known as brain-derived neurotrophic factor (BDNF). BDNF is one of the key molecules that encourage the growth of new brain cells — including, possibly, in the hippocampus, a brain region important in memory and learning. Since the hippocampus tends to be smaller or distorted in people with depression, anxiety and schizophrenia, boosting BDNF through exercise may be one way physical activity might help manage these conditions.

Sure enough, studies show that people with depression have lower levels of BDNF — and, notably, one effect of antidepressant drugs is to increase production of that molecule. Researchers have not yet shown directly that the exercise-associated increase in BDNF is what reduces depressive symptoms, but it remains one of the most promising possibilities, says Hovland.

Exercise may also help anxiety disorders. The brain changes prompted by BDNF appears to enhance learning, which is an important part of some anti-anxiety therapies. This suggests that exercise may be a useful way of improving the effectiveness of such therapies. One of the standard therapies for PTSD, for example, involves exposing patients to the fear-causing stimulus in a safe environment, so that the patients learn to recalibrate their reactions to trauma-linked cues — and the better they learn, the more durable this response might be.

Kevin Crombie, an exercise neuroscientist now at the University of Texas at Austin, and his colleagues tested this idea in the lab with 35 women with PTSD. Researchers first taught the volunteers to associate a particular geometric shape with a mild electric shock. The next day, the volunteers repeatedly saw the same shape without the shock, so that they would learn that the stimulus was now safe. A few minutes later, half the volunteers did 30 minutes of moderate exercise — jogging or uphill walking on a treadmill — while the other half did only light movement, not enough to breathe heavily.

The following day, those who had exercised were less likely to anticipate a shock when they saw the “trigger” shape, Crombie found — a sign that they had learned to no longer associate the trigger with danger . Moreover, those volunteers who showed the greatest exercise-induced increases in BDNF also did best at this relearning.

Although the evidence is not yet definitive, a few studies have suggested that regular exercise may lead to better outcomes in patients with schizophrenia too. Vijay Mittal, a psychologist at Northwestern University, wondered whether working out also might prevent people from developing the disorder in the first place.

Mittal works with teenagers who are at high risk of psychotic disorders such as schizophrenia, but who have not yet progressed to the full-on disorder. In the past two decades, researchers have gotten much better at recognizing such individuals just as they begin to display the earliest signs of illness, such as seeing shadows out of the corner of their eye or hearing indistinct voices when no one is home.

For about 10 percent to 33 percent of these teens, these early signs turn into something more serious. “A shadow might turn into a person,” says Mittal. “A whisper might turn into words. A suspicion that someone is following them might turn into the belief that the government is after them.”

Previously, Mittal had found that the hippocampus is different in at-risk teens who later slid down this slippery slope than in those who didn’t. He wondered whether exercise might help bolster the hippocampus and avert the slide. So his team tested this notion in a sample of 30 high-risk teens, half of whom followed a regimen of aerobic exercise twice a week for three months. (The other half, the control group, were told they were on the wait list for the exercise program.) The researchers used brain scans to look at participants’ hippocampus before and after the program.

The experiment has just concluded, and Mittal is still analyzing the results, which he calls promising. He cautions, however, that exercise is not a panacea. Schizophrenia is a diverse disease, and even if physical activity proves to be protective for some at-risk people, not all are likely to respond to it in the same way. “It’s really important to remember that these disorders are complicated. I’ve worked with people who exercise a lot and still have schizophrenia,” he says.

If Mittal’s work pans out, exercise may allow mental health workers to help a group that isn’t easily treated with drugs. “Someone who’s just at risk of a psychotic disorder, you can’t just give them medication, because that has risks too,” says Firth. “It would be fantastic to have something else in our arsenal.”

Exercise almost certainly has other effects on the brain, too, experts agree. For example, exercise stimulates the release of endocannabinoids, molecules that are important in modifying the connections between brain cells, the mechanism that underlies learning. This may provide another way of enhancing the learning that underlies successful treatment for depression, PTSD and other mental disorders. Indeed, Crombie’s study of exercise in a simplified model of PTSD therapy measured endocannabinoids as well as BDNF, and increases in both were associated with stronger learning responses.

And physical activity also moderates the body’s response to stress and reduces inflammation, both of which could plausibly help improve brain health in people with mental illness. “We have just scratched the surface,” says Hovland.

Moving the body, engaging the mind

But changing the structure of the brain isn’t the only way physical activity can be beneficial for those suffering from mental health conditions. The habit of exercise can itself be beneficial, by altering people’s thought patterns, says Smith.

For people with mental health issues, simply doing something — anything — can be helpful in its own right because it occupies their attention and keeps them from ruminating on their condition. Indeed, one survey of the published literature found that placebo exercise — that is, gentle stretching, too mild to cause any physiological effect — had almost half the beneficial effect on mental health as strenuous exercise did.

Besides just occupying the mind, regular workouts also give exercisers a clear sense of progress as their strength and fitness improves. This sense of accomplishment — which may be especially notable for weight training, where people make quick, easily measurable gains — can help offset some of the burden of anxiety and depression, says Gordon.

If so, playing a musical instrument, studying a language and many other activities could also help people cope with mental health conditions in a similar way. But exercise does more than that, making it one of the best choices for managing mental health. “You can see benefits from doing anything, but the exercise may confer greater benefits,” says Firth.

For one thing, relatively strenuous exercise teaches people to put up with short-term discomfort for long-term gain. People who suffer from anxiety disorders such as PTSD or panic attacks often show a reduced ability to tolerate mental discomfort, so that experiences most people would cope with result in uncontrolled anxiety instead. There’s now emerging evidence that regular exercise builds tolerance for internal discomfort, and this may explain part of its benefit in managing these conditions, Smith says.

Using exercise as a mental health treatment brings some challenges, however. “People with mental illness are also at higher risk of struggling with low motivation,” Firth says. This can make it difficult to organize and stick with an exercise program, and many patients need additional support.

This is often difficult, because psychologists, psychiatrists and other mental health workers are often already overburdened. Plus, prescribing and supervising exercise hasn’t traditionally been within these practitioners’ purview. “We’re telling people, ‘Hey, exercise is helpful,’ but we’re telling it to people who can’t really incorporate it because they often don’t get any training,” Firth says. Exercise referral schemes, which link patients with fitness specialists and structured programs at community leisure centers, have been used in the UK and other places to encourage exercise in people with physical conditions such as obesity and diabetes. A similar approach could be valuable for mental health conditions, Firth says.

Therapists can also help patients persist for the long term by tailoring their exercise prescriptions to each individual’s capabilities. “I always tell patients that doing anything is better than doing nothing, and the best exercise for you is the one you’ll actually do,” Smith says.

The secret, he suggests, is to make sure people stop exercising before they’ve done so much it makes them feel exhausted afterward. “When you feel like crap after exercise, you’re not going to want to do it,” he says, because the brain tags the activity as something unpleasant. It’s far better to have the patient quit while they still have a positive feeling from the workout. “Without even realizing it, their brain tends to tag that activity as something more pleasurable. They don’t dread it.”

Even light activity — basically just moving around now and then during the day instead of sitting for hours at a time — may help. In one study of more than 4,000 adolescents in the UK, Aaron Kandola, a psychiatric epidemiologist at University College London, and his colleagues found that youths who undertook more light activity during the day had a lower risk of depressive symptoms than those who spent more time sitting.

“What we really need are big exercise trials where we compare different amounts against each other,” says Kandola. “Instead, what we have are different studies that used different amounts of activity.” That makes precise recommendations difficult, because each study varies in terms of its patient populations and methods, and follows results for a different length of time. As researchers learn more about the mechanisms linking exercise to mental health, they should be able to refine their exercise prescriptions so that patients are best able to manage their illnesses.

And exercise has powerful benefits for people with mental illness that go beyond its effects on the illnesses themselves. Many struggle with related issues such as social withdrawal and a reduced capacity for pleasure, says Firth. Standard medications reduce some symptoms but do nothing to address these other problems. Exercise — especially as part of a group — can help boost their mood and enrich their lives.

Even more important, people with serious mental illnesses such as severe depression and schizophrenia also are more likely to have significant physical health issues such as obesity, heart disease and other chronic diseases, and as a result their life expectancy is 10 to 25 years lower than that of unaffected people.

“Reducing those health risks is really paramount at the moment,” says Kandola. “That’s the big appeal of exercise: We already know it can improve physical health. If it does have mental health benefits as well, it can be quite an important addition to treatment.”

Knowable Magazine is an independent journalistic endeavor from Annual Reviews.

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Four Fitness Facts to Fuel Your Workout

Things to keep in mind for when you’re low on motivation.

By Melinda Wenner Moyer

There’s rarely enough time in the day to accomplish everything we set out to do, and exercise is often sacrificed when we’re short on time. Federal guidelines recommend fitting two and a half hours of moderate physical activity into our lives each week — and making time for muscle-strengthening exercises.

I sometimes find this guidance daunting, and I’m not alone. Only 25 percent of adults in the United States met those recommendations in 2020. So I grew curious about the research: How much physical activity does a person need to live longer and reduce their risk of chronic disease? How frequently do they actually need to work out?

Exploring the science and talking to researchers generated surprising information, like you don’t need to work out every day, and stretching doesn’t automatically prevent injuries.

Here are four research-based insights about exercise that might make you more excited to put on your workout clothes.

You can keep your workouts short.

The U.S. Department of Health and Human Services recommends that adults get at least 150 minutes of moderate exercise each week from activities like biking or swimming. That corresponds to just over 20 minutes a day. Still, you can benefit from doing less, said Dr. I-Min Lee, an epidemiologist who studies exercise at Brigham and Women’s Hospital in Boston.

The first 20 minutes of physical activity per session confer the most health perks, at least in terms of longevity, Dr. Lee said. As you continue working out, “the bang for your buck starts to decrease” in terms of tangible health rewards, she added.

A study published in March estimated that 111,000 lives could be saved each year if Americans over 40 added just 10 minutes per day to their current exercise regimen.

But what if you only have five or ten minutes to work out? Do it. “A lot of things happen in your body from the second you start to exercise,” said Carol Ewing Garber, a movement scientist at Columbia University Teachers College. And it’s possible to experience mental health benefits , including reduced anxiety and better sleep, immediately after a moderate-to-intense physical activity.

Your workouts don’t have to be intense.

If high-intensity interval training and hard core spin classes make you want to hide, don’t worry. You don’t have to sweat profusely or feel wrecked after a workout to reap some rewards.

Any physical activity that gets your heart beating a little faster is useful. If you’ve never tracked your heartbeat while exercising, it might be worth trying. For moderate exercise, the recommended target is roughly 50 to 70 percent of your body’s maximum heart rate. (To calculate your maximum heart rate, subtract your age from 220.) Many people will hit this target during a brisk walk, said Beth Lewis, a sport and exercise physiologist at the University of Minnesota.

Estimating your maximum heart rate can help you gauge how hard you should be walking, running or cycling. But it’s not perfect, since your natural heart rate during exercise may be higher or lower. Plus, the fitness levels and heart rates among people the same age can vary, and not all exercises raise your heart rate the same amount. Consider talking to your doctor before establishing your goals.

“Just moving your body in some way is going to be helpful,” Dr. Garber said. “That’s a really important message.”

Focus on overall health, not weight loss.

Many people exercise with weight loss in mind, but merely increasing physical activity usually isn’t effective. In a 2011 review of 14 published papers, scientists found that people with bigger bodies who did aerobic exercise for at least two hours a week lost an average of only 3.5 pounds over six months. And in a small 2018 clinical trial , women who did high-intensity circuit training three times a week didn’t see significant weight loss after eight weeks. (They did, however, gain muscle.)

Exercise improves your overall health, and studies suggest that it has a larger effect on life expectancy than body type. Regardless of your size, exercise reduces your risk of heart disease , some kinds of cancer , depression , type 2 diabetes , anxiety and insomnia , said Dr. Lewis.

It’s OK if you can only work out on weekends.

I’ve always assumed that the healthiest exercisers work out almost every day, but research suggests otherwise. In a study published in July, researchers followed more than 350,000 healthy American adults for an average of over 10 years. They found that people who exercised at least 150 minutes a week, over one or two days, were no more likely to die for any reason than those who reached 150 minutes in shorter, more frequent bouts. Other studies by Dr. Lee and her colleagues have drawn similar conclusions .

When it comes to potentially living longer, “it’s actually the total amount of activity per week that’s important,” Dr. Lee said. But, she added, if you work out more frequently, you’re less likely to get an exercise injury.

Stretching is optional.

Recommendations to stretch before and after workouts annoy me, especially if I’m pressed for time. But research suggests that stretching doesn’t actually reduce your risk of injury. “It used to be a required part of what you do — ‘If you don’t stretch, you’re going to get hurt,’” Dr. Lewis said. “That mentality is wrong.”

Instead of static stretching — doing things like touching your toes — Dr. Lewis recommends doing dynamic stretches before you exercise, such as gently swinging each leg forward and back while standing. Static stretching can, however, help increase muscle flexibility and joint mobility, she explained. But now I know not to worry if I don’t have time to do it.

After learning all of this, I’m less stressed by exercise guidelines — and more willing to move my body when I have a moment. Case in point: I’m traveling with extended family this week and have found it hard to schedule time for workouts. But yesterday I did some push-ups; today I walked a few blocks — and that, I now realize, is a lot better than nothing.

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Depression and anxiety: exercise eases symptoms.

Depression and anxiety symptoms often improve with exercise. Here are some realistic tips to help you get started and stay motivated.

When you have depression or anxiety, exercise often seems like the last thing you want to do. But once you get started and keep going, exercise can make a big difference.

Exercise helps prevent and improve many health problems, including high blood pressure, diabetes and arthritis. Research on depression, anxiety and exercise shows that the mental health and physical benefits of exercise also can help mood get better and lessen anxiety.

The links between depression, anxiety and exercise aren't entirely clear. But working out and other forms of physical activity can ease symptoms of depression or anxiety and make you feel better. Exercise also may help keep depression and anxiety from coming back once you're feeling better.

How does exercise help depression and anxiety?

Regular exercise may help ease depression and anxiety by:

• Releasing feel-good endorphins. Endorphins are natural brain chemicals that can improve your sense of well-being.
• Taking your mind off worries. Thinking about something else instead of worrying can get you away from the cycle of negative thoughts that feed depression and anxiety.

Regular exercise has many mental health and emotional benefits too. It can help you:

• Gain confidence. Meeting exercise goals or challenges, even small ones, can boost your self-confidence. Getting in shape also can make you feel better about how you look.
• Get more social interaction. Exercise and physical activity may give you the chance to meet or socialize with others. Just sharing a friendly smile or greeting as you walk around your neighborhood can help your mood.
• Cope in a healthy way. Doing something positive to manage depression or anxiety is a healthy coping strategy. Trying to feel better by drinking alcohol, dwelling on how you feel, or hoping depression or anxiety will go away on its own can lead to worsening symptoms.

Is a structured exercise program the only option?

Some research shows that physical activity such as regular walking — not just formal exercise programs — may help mood improve. Physical activity and exercise are not the same thing, but both are good for your health.

• Physical activity is any activity that works your muscles and requires energy. Physical activity can include work or household or leisure activities.
• Exercise is a planned, structured and repetitive body movement. Exercise can help people get physically fit or to stay fit.

The word "exercise" may make you think of running laps around the gym. But exercise includes a wide range of activities that boost your activity level to help you feel better.

Certainly running, lifting weights, playing basketball and other fitness activities that get your heart pumping can help. But so can physical activity such as gardening, washing your car, walking around the block or doing other less intense activities. Any physical activity that gets you off the couch and moving can boost your mood.

You don't have to do all your exercise or other physical activity at one time. Broaden how you think of exercise. Find ways to add small amounts of physical activity throughout your day. For example, take the stairs instead of the elevator. Park a little farther away from work to fit in a short walk. Or if you live close to your job, consider biking to work.

How much is enough?

For most healthy adults, the U.S. Department of Health and Human Services exercise guidelines recommend at least 150 minutes of moderate aerobic activity a week. Or get at least 75 minutes of vigorous aerobic activity a week. You also can get an equal mix of the two types.

Aim to exercise most days of the week. But even small amounts of physical activity can be helpful. Being active for short periods of time, such as 10 to 15 minutes at a time, throughout the day can add up and have health benefits.

Regular exercise may improve depression or anxiety symptoms enough to make a big difference. That big difference can help kick-start further improvements. The mental health benefits of exercise and physical activity may last only if you stick with them over the long term. That's another good reason to find activities that you enjoy.

How do I get started — and stay with it?

Starting and sticking with an exercise routine or regular physical activity can be a challenge. These steps can help:

• Find what you enjoy doing. Figure out what type of physical activities you're most likely to do. Then think about when and how you'd be most likely to follow through. For example, would you be more likely to do some gardening in the evening, start your day with a jog, or go for a bike ride or play basketball with your children after school? Doing what you enjoy can help you stick with it.
• Get your healthcare professional's support. Talk to your healthcare professional or mental health professional for suggestions and support. Talk about an exercise program or physical activity routine and how it fits into your overall treatment plan.
• Set reasonable goals. Your mission doesn't have to be walking for an hour five days a week. Think realistically about what you may be able to do. Then begin slowly and build up over time. Make your plan fit your own needs and abilities rather than setting goals that you're not likely to meet.
• Don't think of exercise or physical activity as a chore. If exercise is just another "should" in your life that you don't think you're living up to, you'll think of it as a failure. Instead, look at your exercise or physical activity schedule the same way you look at your therapy sessions or medicine — as one of the tools to help you get better.
• Think about what keeps you from being successful. Figure out what's stopping you from being physically active or exercising. If you think about what's stopping you, you can probably find a solution. For example, if you feel self-conscious, you may want to exercise at home. If you stick to goals better with a partner, find a friend to work out with or who enjoys the same physical activities that you do. If you don't have money to spend on exercise gear, do something that's cost-free, such as regular walking.
• Prepare for setbacks and obstacles. Give yourself credit for every step in the right direction, no matter how small. If you skip exercise one day, that doesn't mean you can't keep up an exercise routine and might as well quit. Just try again the next day. Stick with it.

Do I need to see my healthcare professional?

Check with your doctor or other healthcare professional before starting a new exercise program to make sure it's safe for you. Talk about which activities, how much exercise and what intensity level is OK for you. Your healthcare professional can consider any medicines you take and your health conditions. You also can get helpful advice about getting started and staying on track.

If you exercise regularly but depression or anxiety symptoms still affect your daily living, see your healthcare professional or mental health professional. Exercise and physical activity are great ways to ease symptoms of depression or anxiety, but they don't replace talk therapy, sometimes called psychotherapy, or medicines.

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• Tips for starting physical activity. National Institute of Diabetes and Digestive and Kidney Diseases. https://www.niddk.nih.gov/health-information/weight-management/tips-get-active/tips-starting-physical-activity. Accessed Nov. 5, 2023.
• Roake J, et al. Sitting time, type, and context among long-term weight-loss maintainers. Obesity. 2021; doi:10.1002/oby.23148.
• Laskowski ER (expert opinion). Mayo Clinic. June 16, 2021.
• Correia EM, et al. Analysis of the effect of different physical exercise protocols on depression in adults: Systematic review and meta-analysis of randomized controlled trials. Sports Health. 2023; doi:10.1177/19417381231210286.
• Kung S (expert opinion). Mayo Clinic. Dec. 9, 2023.

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41 Exercise Statistics: The Latest Fitness Trends (In 2024)

Only one in five US adults exercise every day, with walking being the most popular way to stay fit. In this article you can learn more about who exercises most, plus you’ll discover the fittest state and the global challenge to get more people moving.

Fitness Statistics (Top Picks)

How many americans exercise each day, what is the most popular type of exercise, what is the most popular group exercise, what percentage of the us is obese, what percentage of americans use fitness apps, what is the size of the fitness industry in the us, why do people not exercise, who exercises more, males or females, who is most likely to go to the gym, how many children exercise in the us, which ethnic group exercises the most, which state works out the most, which state has the least amount of exercise, how big is the at home fitness industry, how many people work out at home vs the gym, what percentage of the world does not exercise, what is the fittest country, which country exercises the least, time to get physical.

• Just one in five US adults exercise each day.
• The US gym, health and fitness club market is estimated to be worth $32 billion.
• More men meet the national standards for exercise , 26.3% vs 18.8%.
• People aged between 18 and 34 years old are the most likely to be gym goers.
• More than three quarters of children in the US are active for less than the recommended 60 minutes each day.
• Colorado is the US state that exercises the most , with the population of Mississippi working out the least .
• The home fitness market in the US is valued at $11.3 billion , and growing year on year.
• 1 in 4 adults around the world don’t meet the globally recommended physical activity levels .

2023 Fitness and Exercise Statistics

Data from Statista reveals that just one in five US adults exercise each day.

In fact, only 23% of US adults get the recommended amount of aerobic and  muscle-strengthening activity  each week.

Focusing on aerobic exercise only , the results are a little more encouraging, with 53.3% meeting the recommendation.

The U.S. Department of Health and Human Services recommends that adults should do at least 150 minutes of moderate-intensity aerobic physical activity each week, as well muscle-strengthening activities.

According to the U.S. Bureau of Labor Statistics, walking is the most popular type of exercise .

30% of active adults choose walking , with weightlifting and using cardiovascular equipment, such as a treadmill or rowing machine , not far behind.

Yoga is the most popular form of  group exercise  in the US.

The latest yoga statistics reveal that 10% of the US population practice yoga , with yoga growing in popularity by 63.8% between 2010 and 2021.

• 42.4% of adults  across the United States are classed as obese.

Information gathered from the National Health and Nutrition Examination found that nearly 1 in 3 adults in the US are classed as overweight , with 9.2% of the population having severe obesity .

86.3 million adults  in the US use a health or fitness app.

This has grown by 38% since 2018, when the number was just 62.7 million.

The gym, health and fitness club market in the US is estimated to be worth $32 billion .

It has declined 4% per year on average since 2017.

A lack of time and motivation were the top reasons given in a OnePoll study into why Americans don’t exercise more.

Being too tired and having too much work to do topped the poll of why adults in the US skip planned workouts .

2023 Fitness and Exercise Key Statistics:

• Just 19.3% of the US adult population exercise each day.
• Walking is the most popular type of exercise, with yoga being the most popular form of group exercise.
• 25% of adults in the US regularly use a health and fitness app.
• A lack of time most common reason given for not exercising.

Sources: Statista | CDC | U.S. Department of Health and Human Services | U.S. Bureau of Labor Statistics | Club Industry | U.S. Department of Health and Human Services | Statista | IBIS World | NY Post

Fitness Demographics Statistics

26.3% of men  meet the national standards for exercise, compared to only  18.8% of women .

Researchers at Seattle Pacific University found that men exercise more for enjoyment , whereas women report exercising for weight loss and toning.

Women aged between 18 and 34 years old are the most likely to go to the gym.

Those in the 18-34 year old age group make up 60% of the gym community , with women very slightly bigger gym-goers than men at 50.5%.

Just 24% of children under the age of 17 meet the CDC’s Physical Activity Guidelines for Americans .

This concerning fact about exercise shows that more than three quarters of children participate in less than the recommended 60 minutes of physical activity each day.

According to data compiled by Statista, Asian Americans and Non-Hispanic Whites are the most physically active ethnic groups in the United States.

The hispanic population record the highest rate of physical inactivity , with 30.6% of this ethnic group reporting a sedentary lifestyle .

Fitness Demographics Key Statistics:

• 26.3% of men meet the national standards for exercise , compared to 18.8% of women.
• People aged between 18 and 34 years old are the age group most likely to go to the gym.
• 76% of children in US don’t meet the recommended daily standard for exercise.
• 30.6% of the hispanic population in the United States report a sedentary lifestyle.

Sources: Finances Online | Medium | National Library of Medicine | CDC | Statista

Fitness Statistics by State

Colorado is the state that works out the most, with 32.5% of the population meeting the national exercise guidelines.

Idaho (31.4%), New Hampshire (30.7%) and Washington D.C. (30.7%) also record having an active population.

Mississippi is that state that has the least amount of exercise , with only 13.5% of the population meeting the national exercise guidelines.

Kentucky (14.6%), South Carolina (14.8%) and Indiana (15.1%) also record lower levels of exercise.

Key Statistics:

• Nearly one-third of the population of Colorado report higher levels of exercise, making it the most active state.
• Just 13.5% of people in Mississippi meet the national exercise guidelines, making it the least active state.

Sources: CBS News

Home Fitness Industry Statistics

The home fitness market in the US was valued at $11.3 billion in 2021 . It’s expected to grow to $17.80 billion by 2030 .

This estimate includes the profits of companies such as Lululemon, a trusted brand for workout clothing, equipment and fitness gifts .

Two in three active people in the US report working out at home , with the remaining third attending a gym.

The confidence to try new fitness activities and the ability to fit their routine around family life , were two of the top reasons given for preferring an at home workout.

72% of adults preferred the flexibility of online fitness classes in particular, allowing them to step away from the commitment of a gym membership.

In fact, the demand for virtual fitness classes is growing year on year , with experts predicting the market will grow by an amazing 35% each year until 2026 .

Changes in the way people exercise has been directly influenced by the pandemic, in fact during 2020 it is thought that nearly a quarter of all gyms in the US closed their doors.

Home Fitness Industry Key Statistics:

Sources: Study Finds | Globe Newswire | Run Repeat | Run Repeat

Global Fitness Statistics

According to the World Health Organization (WHO),  1 in 4 adults don’t meet the globally recommended physical activity levels.

They believe up to five million premature deaths could be avoided each year if the global population was more active.

The WHO guidelines recommend adults should do at least 150 minutes of moderate to vigorous aerobic activity each week.

According to a 2021 global study, the Netherlands has the fittest population.

They spend, on average, more than 12 hours each week exercising or playing sport.

• Brazil has the least physically active population.

They spend, on average, three hours per week on physical activity, compare this to The Netherlands who spend more than 12 hours.

Global Fitness Key Statistics:

• According to the World Health Organization, 1 in 4 adults around the world don’t exercise enough.
• Five million premature deaths could be avoided if the global population was more active.
• The Netherlands has the most physically active population.

Sources: United Nations | World Economic Forum | Ipsos

Want to learn more about the fitness industry in the US?

Here at The Good Body we’ve curated a round up of all the most fascinating Physical Therapy statistics , a few of which might surprise you…

Laura Smith

Associate Editorial Manager

Specialist health & wellbeing writer, passionate about discovering new technologies & sharing the latest research.

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Workout Supplements

A popular category of dietary supplements are workout supplements, which are typically taken before (‘pre-workout’) or after exercising (‘post-workout’), and are sold in a variety of forms from pills to powders and ready-to-drink shakes. The global pre-workout supplement market size alone was estimated to reach $13.98 billion in 2020 and almost double in size to $23.77 billion by 2027. [2]

Fitness gurus and blogs touting these products as crucial for peak performance, fat loss, and explosive muscle growth in combination with complicated scientific-sounding names and labels might have you believing you can’t effectively exercise without them. But do these supplements live up to the hype, and are they even necessary—or in some cases, safe? Like other dietary supplements in the U.S., the Food and Drug Administration (FDA) does not review workout supplements for safety or effectiveness before they are sold to consumers. It’s a good idea to research their effects and ingredients and consult with your physician before adding them to your fitness routine.

What happens to the body during physical activity?

Here we review the scientific evidence behind some of the most popular ingredients in workout supplements.

Pre-Workout Supplements

Pre-workout supplements are designed to provide energy and aid endurance throughout a workout. They are typically taken 15-30 minutes before a workout, but can also be consumed during exercise. Below are common ingredients found in pre-workout supplements that the Academy of Nutrition and Dietetics, Dietitians of Canada, and the American College of Sports Medicine have highlighted as having evidence-based uses in sports nutrition. [3] These supplements have also been categorized as apparently safe and having strong evidence to support efficacy by the International Society of Sports Nutrition. [4] However, it is important to consult a physician or dietitian before using these supplements, as they are not reviewed by the FDA for safety or effectiveness.

Beta-Alanine

Beta-alanine is an amino acid that is produced in the liver and also found in fish, poultry, and meat. When dosed at 4–6g/day for 2–4 weeks, this supplement has been shown to improve exercise performance, particularly for high-intensity exercise lasting 1–4 minutes, such as high-intensity interval training (HIIT) or short sprints. It has also been shown to reduce neuromuscular fatigue, particularly in older adults. [5] How does it work? During exercise the body breaks down glucose into lactic acid, which is then converted into lactate. This produces hydrogen ions, which lower muscle pH levels. This acidity reduces muscles’ ability to contract, causing fatigue. [6] Beta-alanine increases muscle concentrations of carnosine, which is a proton buffer that reduces muscle acidity during high-intensity exercise, which in turn reduces overall fatigue. [5] This supplement is often combined with sodium bicarbonate, or baking soda, which also reduces muscle acidity. A common side effect of beta-alanine supplementation is paresthesia, or a skin tingling sensation, [3] but this effect can be attenuated by taking lower doses (1.6g) or using a sustained-release instead of a rapid-release formula. [5] In short, this supplement can help you exercise at high-intensity for a longer period of time, which could potentially lead to increased muscle mass. The International Society of Sports Nutrition has asserted that “beta-alanine supplementation currently appears to be safe in healthy populations at recommended doses,” but it is important to consult with your doctor before beginning supplementation.

Caffeine is a stimulant that is often included in pre-workout supplements, as it has been shown to benefit athletic performance for short-term high intensity exercise and endurance-based activities. [7] It is important to understand that these studies have been conducted with Olympic and competition athletes, and thus the average individual who exercises recreationally should consult with a doctor before using caffeine as a supplement. For high performance athletes, the International Olympic Committee recommends 3–6mg caffeine/kg of body weight consumed an hour before exercise. [7,8] Evidence also suggests that lower caffeine doses (up to 3mg/kg body weight, ~200 mg) taken before and during prolonged exercise can increase athletic performance. [9,10] Mechanistically, caffeine increases endorphin release, improves neuromuscular function, vigilance, and alertness, and reduces perception of exertion during exercise. [10,11] Despite some benefits from smaller doses, larger doses of caffeine (>=9mg/kg of body weight) have not been shown to increase performance, and may induce nausea, anxiety, and insomnia. [11] The U.S. Food and Drug Administration (FDA) considers 400 milligrams of caffeine to be a safe amount for daily consumption, but some pre-workout supplements may exceed this amount in a single serving or fail to disclose the amount of caffeine they contain, so it is important to always review the label of any supplement before consumption. Caffeine powder is also marketed as a stand-alone pre-workout supplement, but the FDA has advised against using this product, as even very small amounts may cause accidental overdose. Powdered caffeine has been linked to numerous deaths—a single tablespoon (10 grams) is a lethal dose for an adult, but the product is often sold in 100-gram packages. [12]

Creatine is a naturally occurring compound found in skeletal muscle that is synthesized in the body from amino acids and can be obtained from red meat and seafood . In the body, it helps produce adenosine triphosphate (ATP), which provides energy for muscles. Creatine is a popular workout supplement marketed to increase athletic performance, especially for weight training. Research suggests that creatine supplementation increases muscle availability of creatine, which in turn can enhance exercise capacity and training adaptations in adolescents, younger adults, and older adults. [13] Specifically, these adaptations allow for individuals to increase training volume (e.g., the ability to perform more repetitions with the same weight), which in turn can lead to greater increases in lean mass and muscular strength and power. [14-16] Although the exact mechanisms through which creatine improves performance have not been identified with certainty, various theories have been investigated, including the potential for creatine to stimulate muscle glycogen levels. [17,14] Creatine supplementation is primarily recommended for athletes who engage in power/strength exercises (e.g., weight lifting), or for athletes who engage in sports involving intermittent sprints and other brief repeated high-intensity exercises (e.g., soccer, basketball). [13] The International Society of Sports Nutrition recommends an initial dosage of 5g of creatine monohydrate (~0.3g/kg body weight) four times daily for 5–7 days to increase muscle creatine stores; once muscle creatine stores are fully saturated, stores can be maintained by ingesting 3–5 g/day. [13] Many powdered creatine supplements recommend this regimen in the directions on their packages. The Society also notes that an alternative supplementation protocol is to ingest 3g/day of creatine monohydrate for 28 days. [13] While the scientific literature has generally found supplementation to be safe at these levels, [18] creatine may not be appropriate for people with kidney disease or those with bipolar disorder. It is important to consult a doctor before taking this supplement. Of note, creatine supplementation has been shown to increase total body water, which causes weight gain that could be detrimental to performance in which body mass is a factor, such as running. [14] The International Society of Sports Nutrition, the American Dietetic Association, and the American College of Sports Medicine have all published statements supporting creatine supplementation as an effective way of increasing high-intensity exercise capacity and lean body mass during training for high-performance athletes. [19-21;3]

Post-Workout Supplements

A variety of post-workout supplements are marketed to consumers to increase muscle mass through enhanced muscle repair, recovery, and growth. Below is a review of some of the most common ingredients in post-workout supplements.

Carbohydrates

Replenishing glycogen stores after a workout with sufficient carbohydrate intake is important for muscle recovery, and beginning the next workout with sufficient muscle glycogen stores has been shown to improve exercise performance. [22-24] However, normal dietary intake is typically sufficient to restore muscle glycogen stores after low-intensity exercises, such as walking , yoga, or tai chi (3–5 g carbohydrate/kg body weight per day), and even for moderate-intensity exercise, such as one hour or more of walking, jogging, swimming, or bicycling at modest effort (5–7 g carbohydrate/kg body weight per day). [24] Post-workout supplementation with carbohydrates and protein within 24–36 hours is only recommended following strenuous physical activity, which includes one hour or more of vigorous exercise such as interval training, running, swimming, bicycling, soccer, or basketball at a moderate to intense effort (where one can only carry on brief conversations or cannot speak); in this case, 6–12 g carbohydrates/kg body weight per day is recommended to be consumed after exercise to fully restore muscle glycogen stores. [24]

Recommended levels of daily protein intake for the general population (0.8 grams of protein for every kilogram of body weight, or about 7 grams of protein every day for every 20 pounds of body weight) are estimated to be sufficient to meet the needs of nearly all healthy adults. [25] Recommendations for protein supplementation during exercise vary based on the type of exercise being conducted: endurance training (e.g., long-distance bicycling) or resistance training (e.g., weight lifting). Very few studies have investigated the effects of prolonged protein supplementation on endurance exercise performance. A review conducted by the International Society of Sports Nutrition found that protein supplementation in the presence of adequate carbohydrate intake does not appear to improve endurance performance, but may reduce markers of muscle damage and feelings of soreness. [26] On the other hand, individuals who engage in high-intensity resistance training may benefit from increased protein consumption to optimize muscle protein synthesis required for muscle recovery and growth, but research is inconclusive, with the majority of studies investigating the effects of protein supplementation on maximal strength enhancement finding no benefit. [26] The extent to which protein supplementation may aid resistance athletes is highly contingent on a variety of factors, including intensity and duration of training, individual age, dietary energy intake, and quality of protein intake. For individuals engaging in strenuous exercise to build and maintain muscle mass, the International Society of Sports Nutrition recommends an overall daily protein intake of 1.4–2.0 g/kg of body weight/day. [26] This can be ingested in the form of protein foods or protein powder.

Spotlight on protein powder

Some sources of protein supplements:

• Casein and whey are proteins found in cow’s milk ; roughly 80% of milk proteins are casein, while the other ~20% are whey. [28] Both proteins should be avoided by people who have trouble digesting dairy. Casein and whey contain all essential amino acids and are easily absorbed by the body, but their speed of absorption differs. [29,30] Whey protein is water soluble and rapidly metabolized into amino acids. Casein, on the other hand, is not soluble in water and is digested more slowly than whey—when ingested, it forms a clotted gel in the stomach that provides a sustained slow release of amino acids into the bloodstream over several hours. [31] Studies examining protein supplementation for resistance training suggest that whey’s faster digestion could be beneficial for gains in skeletal muscle mass compared to casein in both young men and in trained bodybuilders. [32,33] Another study, however, found that both proteins resulted in increased amino acid concentrations in the body compared to a placebo, with no significant differences between casein and whey for amino acid uptake or muscle protein balance. [34] Due to casein’s slower rate of absorption, it is often touted on health blogs as being useful for weight loss because it could hypothetically promote fullness, especially if ingested before periods of fasting, such as before bed. However, multiple studies have found no clear evidence that casein is more effective than any other protein source for satiety or weight loss. [35,36]
• Soy protein  powder is derived from soybeans , and unlike many plant-based proteins, it contains adequate levels of all essential amino acids. It is a common alternative to milk protein for vegans or people with dairy sensitivities or allergies. Soy protein is absorbed fairly rapidly by the body, although it is not as bioavailable as animal-based proteins. One study found that soy protein promoted muscle protein synthesis significantly more than casein protein when consumed by healthy young men at rest and after leg resistance exercise, but that soy protein was inferior to whey protein in increasing muscle protein synthesis. [32] A review of studies on milk- and soy-based protein supplementation also found that whey protein was better able to support muscle protein synthesis compared to soy protein in younger and older adults. [37]
• Pea protein powder is made from yellow split peas, and can be an option for vegans or people with allergies or sensitivities to soy or dairy. Pea protein is rich in eight of the nine essential amino acids; it is low in methionine, which can be obtained from other sources including rice and animal proteins. There is limited research on the effects of pea protein. One double-blind, randomized, placebo-controlled study found that men aged 18 to 35 years who ingested 50 grams of pea protein daily in combination with a resistance training program over 12 weeks experienced similar increases in muscle thickness compared to those who ingested the same amount of whey protein daily. [38] However, all participants experienced similar increases in muscle strength, with no significant difference between those who supplemented with pea protein, whey protein, or a placebo.
• Hemp protein powder is derived from the seeds of the hemp plant. Although there is little research on the use of hemp protein powder as a workout supplement, it contains omega-3 fatty acids and a number of essential amino acids. However, it is not a complete protein, as it has relatively low levels of lysine and leucine. [39,40]

Branched-Chain Amino Acids (BCAAs)

Three out of the nine essential amino acids have a chemical structure involving a side-chain with a “branch”, or a central carbon atom bound to three or more carbon atoms. These three amino acids, leucine, isoleucine, and valine, are called branched-chain amino acids (BCAAs). They can be obtained from protein-rich foods such as chicken, red meat, fish , and eggs , and are also sold as dietary supplements in powdered form. BCAAs are key components of muscle protein synthesis, [41] and research has shown that leucine in particular drives protein synthesis and suppresses protein breakdown. [42-43] Although short-term mechanistic data suggests that leucine plays an important role in muscle protein synthesis, [44] longer-term trials do not support BCAAs as useful workout supplements. For example, a trial of leucine supplementation during an 8-week resistance training program did not result in increased muscle mass or strength among participants. [45] Studies have generally failed to find performance-enhancing effects of BCAAs such as accelerated repair of muscle damage after exercise. [46]

Another reason to be cautious of a high intake of BCAAs is its potentially negative effect on glucose metabolism and diabetes. BCAAs, particularly leucine, can disrupt the normal action of insulin, a hormone that regulates blood glucose. In an epidemiological study composed of three large cohorts of men and women followed for up to 32 years, a higher intake of BCAAs (obtained mainly from meats) was associated with a higher risk of developing type 2 diabetes. [47]

Chocolate Milk

Although you may not think of it as a “supplement,” a number of pro athletes have begun to promote chocolate milk as an ideal post-workout beverage due to its combination of protein, carbohydrates, water, and electrolytes (in the form of sodium and calcium). A review of the effects of chocolate milk on post-exercise recovery found that chocolate milk provided similar or superior results compared to water or other sports drinks, [48] while another review found that low-fat chocolate milk was an effective supplement to spur protein synthesis and glycogen regeneration. [49] However, the authors noted that evidence is limited and high-quality clinical trials with larger sample sizes are warranted. Of note, many studies of chocolate milk as a post-workout supplement are sponsored by the dairy industry, which may introduce bias. Chocolate milk generally contains high amounts of added sugars and saturated fat, and is likely most useful for athletes conducting high-intensity exercise for multiple hours a day, such as professional swimmers competing in the Olympics. However, for most individuals conducting moderate-intensity physical activity, such as an hour of jogging or bicycling, water is a healthier alternative as a post-workout beverage.

Electrolytes

Many supplements include electrolytes, which are chemicals that conduct electricity when mixed with water, and include sodium, potassium, and calcium. Electrolytes are important for hydration and the regulation of nerve and muscle function; for example, calcium, sodium, and potassium all work together to help muscles contract properly. The body loses electrolytes through sweating, so sports drinks (which typically contain carbohydrates/sugar and electrolytes) and other electrolyte supplements are often marketed as being necessary after a workout. However, the American College of Sports Medicine has asserted that there is little evidence of any difference in performance between those who drink beverages containing carbohydrates and electrolytes compared to those who drink plain water after exercising for less than one hour. [50] Sports drinks and other electrolyte supplements are generally only appropriate for people exercising vigorously for more than an hour, especially if causes them to sweat heavily. Learn more about sports drinks here.

Bottom Line

Workout supplements such as caffeine and creatine may be used to enhance exercise performance for high-intensity, strenuous physical activity, such as training to run a marathon or power lifting. However, a healthy diet with adequate amounts of healthy carbohydrates , protein , and water is sufficient to fuel the body for moderate amounts of physical activity , such as an hour of jogging or bicycling. As workout supplements are not reviewed by the FDA for safety or effectiveness, you should consult with a doctor before incorporating them into your exercise routine and discuss if there are any potential contraindications if you have existing medical conditions.

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Exercise Training and Fasting: Current Insights

Hassane zouhal.

1 M2S (Laboratoire Mouvement, Sport, Santé), University of Rennes, Rennes, F-35000, France

Ayoub Saeidi

2 Department of Exercise Physiology, Faculty of Physical Education & Sports Science, Kharazmi University, Tehran, Iran

3 Department of Medicine Physical and Functional Rehabilitation of the National Institute of Orthopedics “M.T. Kassab”, Tunis, Tunisia

4 Department of Pharmacology, Johannes Gutenberg University Medical Center, Mainz, Germany

M Faadiel Essop

5 Cardio-Metabolic Research Group (CMRG), Department of Physiological Sciences, Stellenbosch University, Stellenbosch, 7600, South Africa

Ismail Laher

6 Department of Anesthesiology, Pharmacology & Therapeutics, Faculty of Medicine, The University of British Columbia, Vancouver, Canada

Fatma Rhibi

Sadegh amani-shalamzari, abderraouf ben abderrahman.

7 Higher Institute of Sport and Physical Education, Ksar-Said, University of Manouba, Manouba, Tunisia

Fasting is defined as the abstinence from consuming food and/or beverages for different periods of time. Both traditional and modern healthcare systems recommend fasting as a therapeutic intervention for the management of several chronic, non-infectious diseases. Exercising during a fasting state increases lipolysis in adipose tissue while also stimulating peripheral fat oxidation, resulting in increased fat utilization and weight loss. A key focus of this review is to assess whether endurance training performed while fasting induces specific training adaptations, where increased fat oxidation improves long-term endurance levels. Fasting decreases body weight, lean body and fat content in both trained and untrained individuals. Several studies indicate a broader impact of fasting on metabolism, with effects on protein and glucose metabolism in sedentary and untrained subjects. However, there are conflicting data regarding the effects of fasting on glucose metabolism in highly trained athletes. The effects of fasting on physical performance indicators also remain unclear, with some reporting a decreased performance, while others found no significant effects. Differences in experimental design, severity of calorie restriction, duration, and participant characteristics could, at least in part, explain such discordant findings. Our review of the literature suggests that there is little evidence to support the notion of endurance training and fasting-mediated increases in fat oxidation, and we recommend that endurance athletes should avoid high intensity training while fasting.

Introduction

The high prevalence of overweight and obesity continues to be alarming, as such conditions are usually accompanied by health complications resulting from metabolic diseases, diabetes, cancer and cardiovascular disease. 1 , 2 This situation is expected to worsen with the rampant spread of physical inactivity. However, fasting and exercise training are non-pharmacological and inexpensive ways to help manage obesity- and overweight-related complications. 3 Many people fast for health, religious or cultural reasons. 2 Fasting is defined as the abstinence from consuming food and/or beverages for different periods of time, which can last from several hours a day to a few weeks. 4 , 5 There is no clear definition of when fasting begins after the last intake of food/drink. 6 Fasting is associated with increased longevity because of its many roles in modifying human health and ageing. 2 Moreover, this unique intervention is considered effective for the management of chronic and acute diseases in both traditional and modern healthcare systems. 7 Fasting is a lifestyle management strategy that benefits several chronic, non-infectious diseases. 7 Fasting and/or physical exercise is often used to investigate the regulation of intermediary metabolism. 6 While prolonged periods of fasting harms health and physical performance, it remains unclear whether shorter or more prolonged periods of intermittent fasting are necessarily harmful. 6

The effect of fasting on the performance of elite athletes started to be investigated in 2007, 8 – 12 stimulated by the belief by many athletes and coaches that fasting negatively impacts on sports performance. 8 , 13 Although various forms of fasting were evaluated to explore the effects on sports performance, Ramadan fasting (as prescribed by the Islamic faith) is garnering increased prominence that is largely due to its unique features. 2 , 8 For example, interest in Ramadan-style intermittent fasting was renewed during the London 2012 Olympic Games and also the FIFA 2014 Soccer World Cup as both events were staged during the month of Ramadan. 6 , 8 , 14 In this narrative review, we discuss the effects of a combination of physical training and fasting on body composition changes, metabolic adaptations and sport performance in untrained and trained subjects.

Literature Search Methodology

A literature search was conducted using four electronic databases (PubMed, ISI Web of Knowledge, Web of Science and SPORTDiscus) from inception until January 2019. The following key terms (and synonyms searched for by the MeSH database) were included and combined using the operators “AND”, “OR”, “NOT”: “fasting”*“body weight”, “body mass”, “body fat”, “weight loss”, “health”, “training”, “exercise”, “endurance”, “performance”, “metabolism”, “glucose”, “lipid”, “protein”, “obesity”, “cardiovascular disease”, “caloric restriction”, “diet”, “restricted feeding”, “Ramadan”. Our search identified 6671 records. Only randomized controlled trials that examined the effects of fasting on performance and selected health indices in healthy sedentary individuals, untrained and trained subjects were eligible for inclusion. Included articles had to be written in English and published in peer-reviewed journals. In addition, the reference lists and citations (Google Scholar) of the identified studies were explored in order to detect further relevant research papers. The final screening was based on the relevance of the identified items for assessing the effect of fasting on health indices and physical capacities of sedentary people and trained subjects.

Study Selection

The final screening done by two investigators was based on the relevance of the identified items for assessing the effect of fasting and training on health indices and physical performances of sedentary or trained people using PICO criteria ( Table 1 ). Overall, our search identified 6,671 records, from which1,261 studies were included after title and abstract screening. 71 articles were included after duplicate and risk of bias checking.

PICOS Criteria

Quality Assessment

The methodological qualities of the studies were assessed by using the PEDro scale with the criteria of >7 in a 11-point PEDro scale ( http://www.pedro.fhs.usyd.edu.au ) which has been shown to have good reliability and validity. Two independent researchers assessed the quality of the studies, and in cases of disagreement, a third researcher assessed the studies and made the final decision on the quality of the studies.

The most frequent form of dietary restriction studied is daily caloric restriction, while other modes such as intermittent fasting is also widely practiced. However, research focusing on intermittent fasting and caloric restriction regimes is not as extensive as religious fasting. 15 Intermittent fasting entails abstinence from food for parts of the day or the week. Energy restriction is the common factor for all the various forms of fasting, even if it is not practiced on a daily basis. Frequently practiced intermittent fasting can be classified into three categories; intermittent calorie restriction (ICR), alternate day fasting (ADF), and time restricted feeding (TRF), with each possessing varying periods of feeding and fasting. 15

Intermittent Calorie Restriction

Intermittent calorie restriction (ICR), also known as whole-day fasting, is the simplest form of intermittent fasting and involves fasting for more than 24h two or three times a week together with ad libitum food intake on the other days, and separated from the next cycle by at least one week. 16 There are two forms of intermittent fasting: 2:5 (caloric restriction for 2 days a week, and a regular diet for 5 days) or 3:4 (caloric restriction for 3 days a week, and a regular diet for 4 days). However, a number of protocols permit food consumption of about 25% (400–600 kcal/day) of total energy expenditure on fasting days.

Alternate Day Fasting

As the practice of intermittent fasting is gaining widespread popularity, there is also increased promotion of alternate day fasting (ADF). 17 , 18 The ADF program involves alternating non-fasting days where participants consume food ad libitum followed by fasting days where only 25% of the usual dietary intake is consumed (~500 kcal). 18 , 19 Of note, a number of ADF protocols do not allow any caloric intake on fast days. 20

Time Restricted Feeding

While fasting requires abstinence from food consumption, a number of intermittent fasting protocols allow for the intake of relatively small quantities of food (~25% of daily caloric needs) during fasting times. 16 Time restricted feeding (TRF) involves a set number of hours of daily fasting, while feeding is permissible during the remaining hours. TRF has three variants: 16/8 (16-h fast, 8-h feeding window), 18/6 (18-h fast, 6-h feeding window), and 20/4 (20-h fast, 4-h feeding window). The rationale for TRF centers around circadian rhythms as recent work outlined the importance of chrono-nutrition, which is the interaction between meal timing and the circadian system that regulates physiology, metabolism and behavior. 21 Fasting during the month of Ramadan is one of the five pillars of Islam and is an extensively studied example of a timed dietary approach that falls under the TRF umbrella. 7 Ramadan is the ninth month of the Islamic lunar calendar and daily abstinence from food and fluid intake occurs from dawn to sunset for the duration of this month. 19 The duration of the fasting period is significantly influenced by the geographical location and season, and commonly lasts from 10 to 18h. 19

The main differences between these protocols are the severity of caloric restriction, the abstinence from food/beverages per day and the frequency of caloric restriction per week. For ADF, an individual alternates ad libitum feeding days with fasting days, which typically consist of one meal consumed at lunchtime that contains approximately 25% of the baseline caloric needs for the individual. For most TRF protocols, a person fasts for a number of hours (16–20 h) and feeding occurs during the remaining hours (4–8 h) in a day. Whole day fasting protocols involve complete fasting or severe caloric restriction for one or two non-consecutive days per week. 15

Acute Effects of Fasting

While fasting is associated with a coordinated set of metabolic changes designed to conserve carbohydrates and increase the reliance on fat as a substrate for energy supply, there is also a decline in cognitive behavior. 22 There are marked metabolic changes that occur while fasting. Glucose levels are elevated during and about 6 h after eating but remain low for the remaining 16 h until the next meal. The rate of blood glucose utilization by tissues is ~ 2 mg/kg/min in the post-absorptive state. A modest reduction in serum glucose levels can occur within a few hours of fasting (fasting glucose levels of 3.3 and 3.9 mmol/L; normal range 3.5–5.5 mmol/L), likely due to attenuated hepatic glycogen synthesis and glycolysis. Such modifications occur due to decreased insulin concentrations and also increased glucagon levels together with enhanced sympathetic activity. 23 During the fasting window the systemic levels of free fatty acids (FFA) and ketones are increased together with an activation of gluconeogenesis (from amino acids, glycerol and ketone bodies). 6 Fasting also attenuates circulating insulin and insulin-like growth factor-1 levels and raises circulating glucagon levels due to hepatic gluconeogenesis. In fasting conditions, FFA and ketones are the main sources of energy for cells and this transition is called intermittent metabolic switching or the glucose-ketone (G-to-K) switchover. Inverse switching, i.e., ketone-glucose (K-to-G) occurs after eating a meal. 6 By contrast, starvation (short term) increases levels of acylcarnitine species and the oxidized amino acid dimer cystine, and decreases plasma tryptophan, choline phosphate, hippuric acid and glycerophosphocholine levels. Moreover, although protein metabolism constitutes a relatively minor contribution to energy supply with normal feeding, its proportion markedly increases with severe calorie restriction. A decline in cognitive function during fasting may be due to decreased blood glucose levels. 19 , 22

Chronic Effects of Fasting

Fasting protocols and body composition.

Details of fasting studies are summarized in Tables 2 – 5 according to the various categories used. The findings from six ICR studies are summarized in Table 2 , and represents a combination of intermittent fasting and caloric restriction (hypocaloric diet), or modified fasting that allows for a small quantity of food intake even on fasting days. There were significant decreases in body weight, 24 , 25 and body fat, 26 , 27 with the exception of the study by Fitzgerald et al (2018). 28 Such variability in ICR was likely due to a number of factors: not all subjects in ICR studies fast the same number of days per week, as some fasted one day per week, 26 while others fasted for 2 days that were either consecutive, 28 or nonconsecutive. 24 , 25 The data generated thus did not suggest which of these ICR protocols elicited the greatest impact. Additional confounding factors included age, weight and gender, as ICR studies generally included middle-aged or older adults. 15

Effect of Alternate Day Fasting on Body Composition

Abbreviations: ADCR, Alternate Day Caloric Restriction ADF, Alternate Day Fasting; ADF-HF, Alternate Day Fasting with High Fat ADF-LF, Alternate Day Fasting with Low Fat; BMI, Body Mass Index; CR, Caloric Restriction; E-ADF, Exercise With Alternate Day Fasting; EX, Exercise; n, number; NC, No Change; NS, Non-Significant.

Intermittent Caloric Restriction and Body Composition

Abbreviations: BMI, Body Mass Index; CCR, Continuous Caloric Restriction; CG, Control Group; CR, Caloric Restriction; DCR, Daly Caloric Restriction; FCR, Fasting Caloric Restriction; ICR, Intermittent Caloric Restriction; IFCR-F, Intermittent Fasting Caloric Restriction food based; IFCR-l, Intermittent Fasting Caloric Restriction Liquid based; n, number; NS, Non-significant.

Effects of Ramadan Fasting on Body Composition

Abbreviations: BMI, Body Mass Index; FG, Fasting Group; NFG, Non Fasting Group; RF, Ramadan Fasting; n, Number; NC, No Change; NS, Non Significant.

The data in Table 4 show that body weight, 30 , 31 fat mass, 32 , 33 and also fat free mass, 32 are significantly lowered by ADF. Moreover, ADF-mediated weight loss occurred in obese and overweight individuals, 30 , 34 and also in normal-weight persons. 35 Variations in results may be related to differences in study design, duration of fasting, subject characteristics, as well as differences in weight (normal weight, overweight, obese), age, and gender. Older adults, obese individuals and women can experience a greater reduction in weight and loss of percentage fat body after fasting. In addition, some studies allowed no caloric intake on fasting days, 36 while others allowed for reductions in caloric intake by up to 70–75%. 37 , 38 Regulating macronutrient intake and adherence to dietary instructions can also influence study outcomes. Another factor to consider was that the majority of ADF studies were completed in animals, 37 , 38 likely due to the difficulty in controlling all parameters within humans. 21

Effect of Time Restricted Feeding on Body Composition

Abbreviations: BMI, Body Mass Index; IF, Intermittent Fasting; ND, Normal Diet; TRF, Time Restricted Feeding; n, number; NC, No Change; NS, Non-Significant.

The outcomes of TRF studies in humans are shown in Table 4 , which does not contain data from religious fasting. The results vary from significant decreases in body weight and fat mass, 41 – 43 to no significant changes. 44 , 45 There are a number of reasons for such differences as fasting periods lasted either for two 46 or eight weeks, 42 , 43 with variations in the number of fasting hours, participant weights (normal weight, overweight, obese), age, gender and also caloric intake.

Several studies reported decreases in body weight with fasting during Ramadan 47 ( Table 5 ). A systematic review of 35 studies 48 reported that Ramadan fasting produced a fairly small but significant weight loss (−1.24 kg; 95% confidence interval:)- 1.60, - 0.88 kg() in both sexes, with most of the weight loss then restored within a few weeks after Ramadan. 49 However, others failed to observe significant changes in body weight during Ramadan, 49 while some even described weight gain during this period 49 ( Table 5 ); these inconsistencies may be due to varied eating routines, socioeconomic status, differences in the number of fasting hours, ethnicity, gender, and the health status and the medical history of participants. 37 , 48 , 50

Fasting Protocols and Metabolic Adaptations

It is clear that that intermittent fasting, especially in the case of Ramadan fasting, benefits lipid metabolism in healthy subjects, 72 – 74 as was also the case for other TRF protocols. Changes in protein, lipid and glucose metabolism and associated hormonal responses were studied during Ramadan fasting (see Table 6 ). Fasting attenuates serum low-density lipoprotein-cholesterol (LDL-C), total cholesterol (TC), triglycerides (TG), while increasing high-density lipoprotein-cholesterol (HDL-C) levels. 54 Other studies reported little or no changes in TC 47 or TG 75 after Ramadan fasting, or in HDL-C and LDL-C levels following an ADF protocol. 35 For example, Beltaifa et al (2002) 76 reported no changes in plasma lipids after Ramadan fasting, while Shephard (2013) 77 found decreased HDL-C and increased LDL-C and TG levels. A meta-analysis by Kul et al (2014) 78 showed that Ramadan fasting decreased LDL-C levels, but did not change HDL-C and TG levels. Furthermore, two studies related to ICR and Ramadan fasting found no changes in lipid metabolism in obese and overweight subjects. 29 , 37 However, this was not the case for ADF where some changes were measured. 18 , 32 , 40

Effect of Fasting on Metabolic Adaptations in Trained and Untrained Subjects

Abbreviations: ADCR, Alternate Day Caloric Restriction ADF, Alternate Day Fasting; ADF-HF, Alternate Day Fasting with High Fat ADF-LF, Alternate Day Fasting with Low Fat; BMI, Body Mass Index; CR, Caloric Restriction; CCR, Continuous Caloric Restriction; E-ADF, Exercise With Alternate Day Fasting; EX, Exercise; FCR, Fasting Caloric Restriction; FG, Fasting Group; HDL-C, High Density Lipoprotein; ICR, Intermittent Caloric Restriction; LDL-C, Low Density Lipoprotein; n, number; NC, No Change; ND, Normal Diet; NFG, Non Fasting Group; NM, Not Mentioned; NS, Non Significant; TC, Total Cholesterol; TG, Triglycerides; TRF, Time Restricted Feeding.

There may be a number of reasons for the differences reported on the effects of IF. Studies varied in experimental design (ICR, ADF, TRF, “Ramadan”), fasting duration, and participant characteristics (normal weight, overweight, obese, age, and gender). 15 Macronutrient intake was also not controlled in most studies, 15 while there were disparities in dietary habits depending on cultural rituals and the number of fasting hours, which can also affect metabolic regulation. 75 It was evident that the data were related to the feeding behavior or biochemical responses to fasting. 54 In fact, some biochemical parameters (lactate dehydrogenase, blood glucose, aspartate aminotransferase, alanine aminotransferase creatine kinase, lactate) were higher in the evening than in the morning, and their responses to exercise were higher in the evening. However, no diurnal variations were observed in resting values of the selected biochemical parameters during the fourth week of Ramadan. 80

Alterations occur in carbohydrate metabolism during IF. The post-absorptive period occurs 8 to 16 h after eating, and represents an adaptation to fasting to ensure sufficient glucose supply to the brain and other vital organs. Several studies reported decreased glucose metabolism in healthy subjects after ADF 72 , 82 and after Ramadan fasting. 53 , 72 , 73 , 81 , 83 Some found a reduction in blood glucose levels after 12 h and 72 h of fasting, 79 while others reported no changes. 25 , 74 However, the meta-analysis by Kul et al 78 concluded that Ramadan fasting reduced blood glucose levels. As summarized in Table 6 , there were no significant changes in blood glucose levels of obese individuals after intermittent fasting. 18 , 30 , 32 However, some studies found that highly trained athletes displayed improved glucose metabolism after intermittent fasting, 58 while other studies failed to confirm this. 67 , 76

Changes in protein metabolism during IF are not as well studied. Three studies indicated no reductions in plasma protein concentrations in healthy subjects during Ramadan ( Table 6 ). 70 , 76 , 79 However, ADF elicited no effects on protein metabolism in obese subjects ( Table 6 ), while other studies reported loss of fat free mass 3 , 84 which may be related to protein catabolism. Gluconeogenesis is the main cause of lean tissue loss in athletes. The work by Chaouachi et al (2008) 64 demonstrated that when Judoka athletes ingested regular amounts of protein (1.6 g/kg), there was a 0.6 kg decline in lean tissue mass after Ramadan. In support of these findings is a study of nine Tunisian rugby players reporting decreases in plasma protein levels by the end of Ramadan at rest and after exercise. 67 However, Soeters et al (2009) 45 reported that short term ADF (alternating between 20 h fasting and 28 h feeding) did not influence whole body protein metabolism in lean healthy men, as they suggested that protein catabolism started on the third day of fasting, while energy utilized during the first 2–3 days of fasting was largely derived from glycogen and fat metabolism. 15 Overall, the results varied between significant to non-significant modifications in protein metabolism, and the reasons were likely similar to studies to assess glucose and lipid metabolism.

The body undergoes transient metabolic adaptations during Ramadan, including improvements in lipid profiles and decreased glycemia. Chennaoui et al (2009) 63 investigated eight middle-distance athletes (aged 25.0 ± 1.3 years and who trained 6 to 10 times per week for at least 3 years) and measured the maximal aerobic velocity 5 days before, during, and after Ramadan. Blood samples were collected before and after Ramadan fasting. This study confirmed increases in circulating FFA levels at the end of Ramadan fasting (from 87±20 to 203±90 µmol.L –1 ) (P<0.05) in endurance athletes, although other metabolic parameters such as TG (from 0.97±0.08 to 0.90±0.13 mmol.L –1 ), TC (from 4.29±0.23 to 3.83±0.12 mmol.L –1 ), HDL-C (from 1.63±0.16 to 1.75±0.18 mmol.L –1 ) and LDL-C (from 2.22±0.17 to 1.67±0.21 mmol.L –1 ) remained unaltered. There were significant changes in hormonal and inflammatory markers, for example increased catecholamine and IL-6 concentrations and lower melatonin levels. Concentrations of IL-6 correlated positively with catecholamine and FFA levels, but negatively with insulin levels. Chennaoui et al (2009) 63 suggested that the IL-6 and catecholamine responses are influenced by alterations in the sleep and eating patterns inherent to Ramadan.

The effects of fasting on sportsmen versus sedentary individuals were investigated by Ba et al (2005) 85 in a study of 30 participants (average age of 25 years) who were randomized to form two groups of 15 subjects each. All participants followed the same eating routine and glycemia was measured twice; during the second fortnight of Ramadan (15 mins before eating), and two months after Ramadan (at least 4 h after the last meal). Resting glycemia in the sportsmen (4.6±0.15 mmol/L) was similar to normal (non-trained) subjects (4.5±0.01 mmol/L) during the month of Ramadan. Moreover, a similar pattern was observed in glycemic levels after normal dietary intake (4.8±0.2 mmol/L and 4.8±0.4 mmol/L for sportsmen and normal subjects, respectively). Participants in the sedentary group returned to normal dietary intakes and also had an increased weight gain after Ramadan, leading the authors to conclude that Ramadan fasting elicited little effect on glucose metabolism in endurance athletes compared to inactive subjects, suggesting that athletes were better able to regulate their glucose metabolism.

Fasting Protocols and Performance

There are a limited number of studies on the effects of fasting on the endurance performance of trained athletes ( Table 7 ), with findings of decreases, 63 , 86 or no changes 87 , 88 in endurance performances after Ramadan fasting. To the best of our knowledge, only a study by Asl (2011) 46 reported a small increase in endurance performance, while other studies suggested that Ramadan fasting negatively affected the endurance performances of athletes. 63 , 89 The reasons for such contradictory findings remain unclear, but a combination of factors such as sleep deprivation or fatigue during Ramadan are important considerations. A study by Aziz et al (2010) 89 reported that Ramadan fasting did not influence all individuals equally, with relatively fitter individuals better able to resist the physiological and psychological perturbations sometimes observed. This may also help to explain discordant findings such as by Brisswaleter et al (2011) 87 and Png et al (2014) 88 who reported limited changes in endurance performance after Ramadan fasting. The study by Brisswaleter et al (2011) 87 reported decreased muscular performance and increased oxygen kinetics with Ramadan fasting, but without changes in VO2max or performance in middle-distance runners. By contrast, Asl (2011) 46 investigated the effects of Ramadan fasting on endurance running performance in male athletes, finding that Ramadan fasting elicited positive effects on endurance performance. The participants were tested twice (30 mins running on the track), with the first test performed one week before Ramadan and the second in the middle of the month of fasting. There were no significant changes in body weight, body mass index, fat free mass, body fat, urinary density, mean heart rate and lactate threshold (all p>0.05). Moreover, the finding revealed that Ramadan fasting had a small but significant impact on endurance running performance. 46

Effects of Fasting on Endurance Performances in Endurance Trained Athletes

Abbreviations: HR, Heart Rate; MAP, Maximal Aerobic Power; MAV, Maximal Aerobic Velocity; n, number, NC, No Change; NS, Non-Significant; RPE, Rating Perceived Exertion.

There are only a limited number of studies on the effects of fasting on endurance performances in untrained and non-endurance-trained athletes but with conflicting findings (as summarized in Table 8 ). Some observed no changes 62 , 64 , 91 while others reported increased, 9 , 10 , 92 or impaired performances. 11 , 54 , 92 For example, Chaouachi et al (2008) 64 reported no changes in endurance performances of judo athletes, although the lack of information on total energy and macronutrient intake in some studies makes it difficult to compare the findings with others. Moreover, studies by Fouad (2008) 91 and Chaouachi et al (2009) 64 did not observe differences in the performance of soccer players measured during a maximal aerobic test or endurance time performance at 85% of maximal oxygen uptake (VO 2 max). However, the authors suggested that the small (but insignificant) increase in endurance time maybe related to the preferential use of lipids over carbohydrates; however carbohydrate metabolism in this instance was associated with muscle fatigue and hyperventilation, leading to dyspnea. 8 , 91 As aerobic performance was not influenced by fasting, Fouad (2008) 91 suggested that sportsmen adapt to a new physiological regulation of metabolism after three weeks of fasting.

Effects of Fasting on Physical Performances in Untrained Subjects and Non-Endurance Athletes

Abbreviations: HR, Heart Rate; NC, No Change; NS, Non-significant; RPE, Rating Perceived Exertion; RRT, Recognition Reaction Time; TRT, Total Reaction Time.

Other studies indicated decreased endurance performances in response to Ramadan fasting. 11 , 54 , 92 For example, Hammouda et al (2014) 54 demonstrated a significant decrease in distance covered during the Yo-Yo level 1 test (measures ability to perform the longest distance covered during repeated interval runs) after Ramadan fasting in male professional soccer players. This can largely be explained by fuel substrate selection during the exercise period, level of physical conditioning and regular physical training. At the same time, it should also be stressed that there was an increased tendency to consume calorie-rich dietary intake and energy-dense drinks by some athletes after breaking their fast. 62 There was also a decreased aerobic capacity in young soccer players as noted by increases in their mean 3,000 m running times after the Ramadan fast, 11 which may be related to the training program of the soccer players that was modified during Ramadan fasting. There was a tendency of favoring lower intensity and reduced tactical training during Ramadan fasting. Collectively, such changes in daily routines will decrease physical capacity of athletes by the end of Ramadan.

Training and Fasting

It is now increasingly recognized that physical training and fasting have beneficial effects on body composition and health. 93 , 94 Aerobic exercise training and fasting are two well-known strategies to increase lipolysis in adipose and muscle tissue, and thereby reduces the amount of body fat mass. This is important for athletes, as they need to control their body composition to optimize the balance between lean and fat body mass so as to improve their performances. 95 , 96

Fat and carbohydrate are the most important fuel substrates for skeletal muscle ATP synthesis during aerobic metabolism. 90 Endurance capacity is determined by maximal cardiac output together with the oxidation of fat and carbohydrate stores. Exercise duration is limited by skeletal muscle metabolism and the relatively limited glycogen storage depots. Fatigue occurs when the rate of fat utilization is insufficient to meet energy demands. To counter this, athletes may consider an improved metabolic training regimen for events lasting for more than 2 hrs with the aim of increasing glycogen storage and enhancing fat oxidation capacity. 97 We next discuss the physiological effects of exercise when fasting.

Untrained Subjects

Exercise with fasting: metabolic regulation.

Fasting lowers circulating insulin levels and increases hepatic glycogen breakdown, 6 suggesting that endurance training during this state leads to greater fat utilization compared to the fed state. 4 , 98 Fat is the main fuel source used during exercise when fasting, when plasma glycerol and FFA levels increase due to activation of lipolysis in adipocytes. Fat burning pathways are activated by catecholamines (binding to beta-adrenergic receptors) and glucagon, and is inhibited by insulin. This makes blood glycerol and FFA levels useful markers of adipocyte lipolysis. Plasma levels of glycerol increase slightly at low levels of exercise, but are significantly greater during fasting. During low intensity exercise, glycerol levels during a fed-state is 5.5 mmol/kg/min while these reach 8.5 mmol/kg/min during a fasting state. 4 , 5 Similarly, with low intensity exercise plasma FFA concentrations reach 0.20 mM in the fed-state and 0.45 mM in the fasting state. 4 , 5 Exercising during the fed state attenuates fat oxidation due to higher post-prandial insulin concentrations 96 , 99 ( Figure 1 ).

Exercise in fasted compared to fed states. Aerobic exercise performed in the fasted state induces higher fat oxidation than exercise performed in the fed state.

Abbreviations: NEFA, non-esterified fatty acids; ATGL, adipose triglyceride lipase; HSL, hormone-sensitive lipase; CD36, fatty acid translocase; CPT-1, carnitine palmitoyltransferase-1; UCP-3, uncoupling protein 3; AMPK, AMP-activated protein kinase; SIRT1, sirtuin-1.

By contrast, exercising during the fasting state increases adipose tissue lipolysis and peripheral fat oxidation via higher plasma adrenaline and cortisol concentrations and lower circulating insulin levels. 10 , 12 – 15 These stress hormones interact with adipose tissue to phosphorylate adipose triglyceride lipase and hormone-sensitive lipase enzymes, which triggers lipolysis to increase circulating FFA levels. By contrast, exercise training in a fasting state leads to up-regulation of genes involved in fatty acid transport (e.g. fatty acid translocase/CD36; carnitine palmitoyltransferase-1) and β-oxidation (e.g. uncoupling protein 3, AMP-activated protein kinase) in muscle fibers, 73 thereby resulting in enhanced skeletal muscle fat oxidation. 83 In support, there is an increased rate of fat oxidation at rest after training while in a fasting state (versus the same exercise performed post-prandially), and leading to decreased body fat content. 8 In contrast, feeding before exercise increases insulin levels (which can remain elevated for about 3 h) and can attenuate the metabolic responses (such as lipolysis enzymes, fatty acid transports and fat oxidation) induced by exercise during a fasting state ( Figure 1 ).

These findings support the concept that performing endurance training while fasting increases fat oxidation and promotes long-term adaptations that are beneficial to overall health and well-being. 100 Of note, hepatic glycogen stores are mostly depleted after fasting periods if no exogenous carbohydrates are supplied. Dysregulation of glucose metabolism and hypoglycemia can also occur with prolonged exercise. 100 – 102 However, regular exercise when fasting can induce specific physiological adaptations to facilitate glucose homeostasis despite a limited hepatic glycogen availability. 100 Thus many endurance athletes perform their training sessions after an overnight fast, hoping to increase performances by changing their fuel substrate selection. 100 However, it should be kept in mind that there are only a few studies that have examined the effects of fasting on physical performances and the results obtained so far are inconclusive. 8

Exercise with Fasting: Performance

The effects of short-term fasting on exercise performances have been extensively investigated 6 , 103 – 110 and suggest that decreased physical performances occur during the fasting state. 8 This could be explained (at least in part) by the fasting periods used (>24 to 55 h), dehydration, 109 prolonged exhaustive exercise testing, 103 , 104 , 107 and/or very high-intensity levels of exercise. 104 , 110 However, others 108 , 109 , 111 , 112 failed to record significant decreases in performance after shorter periods of fasting (11–24 h). For example, studies by Van Proeyen (2011) 100 and Stannard et al (2010) 113 indicated that habitual fasted training on sedentary and untrained subjects was a positive strategy to stimulate physiological adaptations in muscle that could improve endurance exercise performance. It is important to note that the majority of these studies investigated recreationally active or untrained subjects 8 making it difficult to extrapolate these findings to highly trained athletes.Others reported significant reductions in running distance by the second week of Ramadan, although the distances returned or exceeded the baseline values by the fourth week. 10 This was dissimilar to the findings Meckel et al (2008) 11 who suggested that reduced endurance when fasting was likely due to the decline of soccer training intensity. Of note, in the study by Kirkendall et al (2008) 10 all players trained on the same days and the number, intensity, and duration of training was similar to the rest of the year. Their data showed an initial decline in performance that returned to, or even exceeded pre-fasting values by the end of Ramadan. This phenomenon may be related to alterations in training, lifestyle, diet, and sleep patterns after the first two weeks of Ramadan. 10

It is possible that modifications in endurance performances during Ramadan are not limited to altered training patterns. The physiological adaptations in fasting subjects during the month of Ramadan could also be account for by improved athletic performances. In fact, Sweileh et al (1992) reported that metabolism in fasting individuals slows down during Ramadan to likely conserve energy stores. 92 Serum sodium, chloride, and protein levels increased during the first week of Ramadan (implying that the subjects were likely dehydrated during this period), with subjects losing ~ 1.13 kg body weight without changes in percent fat. These acute biochemical changes prevent catecholamine release and decreases venous return, thereby resulting in reductions in sympathetic tone, blood pressure, heart rate, and cardiac output. 92 Such physiological adaptations can also influence physical work capacity and athletic performances as shown by the significant decrease in VO 2 max during the first week of Ramadan. These biochemical changes returned to baseline values during the last week of Ramadan while VO 2 max returned to pre-fasting levels.

Trained Subjects

Most reviews on fasting and athletic performance focus on fat and carbohydrate metabolism in healthy untrained subjects, 96 , 114 , 115 with some also evaluating body composition changes in untrained subjects. Moreover, studies on exercise by highly trained athletes did not take body composition changes into account.

Exercise with Fasting Protocols: Metabolic Regulation

Fat and carbohydrate are the most important fuel substrates for skeletal muscle ATP synthesis during aerobic metabolism. 90 Endurance capacity is associated with maximal cardiac output together with the oxidation of both fat and carbohydrate stores. The duration of exercise is limited by skeletal muscle metabolism and the relatively limited glycogen storage depots within the body. Fatigue occurs when the rate of fat utilization is insufficient to meet energy demands. To counteract this, athletes may consider an improved metabolic training regimen for competitive events lasting for more than 2 hrs, aimed at increasing glycogen storage and enhancing fat oxidation in this case. 97

Although the studies cited above were conducted on healthy, sedentary subjects, some studies explored the effects of fasting on lipid metabolism in highly trained subjects. For example, Chaouachi et al (2008) 64 found modifications in serum lipids (increased HDL-C, LDL-C and TC) in elite judo athletes. Moreover, Mirzaei et al (2012) 58 reported increased HDL-C levels together with lower LDL-C and TC levels in wrestlers at the end of Ramadan fasting. In support, others found improvements in HDL-C and LDL-C in resistance-trained subjects after TRF. 42

Exercise with Fasting Protocols: Performance

Endurance training while fasting represents a novel strategy to induce specific training adaptations by increasing fat oxidation during exercise and by enhancing physical performances in the long-term. 100 Endurance training in a fasted state can trigger positive effects on endurance performance in untrained 100 , 103 and endurance trained athletes 116 ( Table 9 ).

Effect of Endurance Training on Fast State on Endurance Performance

Abbreviations: MAV, Maximal Aerobic Velocity; n, number; NS, Non-Significant.

In fact, regular exercise training in the fasted state stimulates the contribution of intramyocellular lipids to energy provision through fasting endurance exercise. 100 Training in a fasted state also increases muscular oxidative capacity to a greater extent than other comparable exercise intensities and duration with sufficient exogenous carbohydrate supply. A study by Bouguerra et al (2017) 116 investigated the effects of Ramadan fasting on maximal aerobic velocity, time to exhaustion, and performance for a 3000 m exercise in three different groups of highly trained runners: a) group who trained in the afternoon (between 2:00 and 4:00 pm), b) in the morning (between 09:00 and 11:00 am), and c) in the evening (between 10:00 and 12:00 pm). Their findings revealed that maximal aerobic velocity and VO 2 max were significantly higher (p< 0.01) in the afternoon and morning compared to the evening before, when measured mid-, and post-Ramadan. The performances for the 3000 m running exercise (before and after Ramadan) were higher (p < 0.01) and the time to exhaustion lower (p < 0.001) in the evening and morning compared to the afternoon. The authors concluded that training in the afternoon during Ramadan can more effectively enhance aerobic performance compared to morning or evening training. 116 The superior physical outcomes during the afternoon could be due to the normal diurnal or circadian rhythm of sport performance, 116 increased muscle temperature, 117 a greater mobilization of glycogen and an increased use of FFAs as a fuel substrate during afternoon exercise sessions. 118 However, additional research is needed to confirm that endurance training performed while fasting may indeed increase endurance performances in highly trained athletes.

Practical Applications

The available data suggest that exercise in a fasting state decreases body weight, free fat mass and fat mass, although more controlled studies are needed for definitive recommendations to be made. A moderate intensity exercise during fasting is recommended for the prevention of hypoglycemia. Training in the evening while fasting may be more effective in enhancing aerobic performance, compared to training in the morning. Athletes may wish to train in the fasting state in the pre-season as fasting increases the activity of fat-burning enzymes. However, fasting can elicit negative effects on performance in some events, and hence modifications to the training schedules (eg fasting during the pre-season) may minimize such effects.

Conclusions

This review of the literature identified that the effects of fasting on endurance athletic performances requires further investigation. Different fasting programs influences human physiological and biochemical parameters that are important for athletic performances. The collective data suggest that different fasting practices (ICR, ADF and TRF) decrease body weight and fat 7 , 27 in both trained and untrained subjects. Moreover, several studies demonstrated that fasting alters protein, lipid and glucose metabolism and associated hormonal responses. However, the conflicting findings related to glucose metabolism in response to fasting in highly trained athletes require further investigation. Studies on the effects of fasting on indicators of physical performance have generated conflicting data. For example, some studies reported decreased performances while others showed no effect. There are a number of reasons for such differences, including variations in experimental design, fasting duration, and unique participant characteristics. We suggest that athletes train at relatively low intensities (and not at high intensity levels) when fasting to ensure that they recover adequately to optimize performances in competitive events. Our analyses also revealed a major weakness in that most fasting studies recruited sedentary subjects or low-level athletes, often without well-matched controls. We recommend that well-controlled studies are required to improve our understanding of the effects of exercise in fasting athletes, and to help uncover novel insights into the mechanisms driving changes in energetic pathways and physical performances in trained endurance athletes that choose to fast.

The authors report no conflicts of interest in this work.

The health benefits of working out with a crowd

We've all seen it happen: finding the motivation to actually make it to 6 a.m. boot-camp with a friend; nailing the last round of squats when you see those around you powering through; or pushing yourself to shave time off your personal record when you run a 5k race. There is something to be said about the power of working out in a group — but what is it about exercising with others that motivates us?

We tapped some experts on the topic and learned that when it comes to workouts, there’s some truth to the old adage, “There’s strength in numbers.”

One study found that 95 percent of those who started a weight-loss program with friends completed the program.

“Group activity may not be a new concept but it has certainly seen massive international up-trends over the last twenty years with rapidly rising numbers in spin cycling, aerobic and dance-based classes and the emergence of CrossFit and its tribe mentality,” says Rob McGillivray, personal trainer and founder of RETROFIT . “I believe it to be a key indicator that working out in a motivational pack or using it as a tool to enhance internal or external competitive performance is fast becoming the preferred form of exercise.”

Not only is group fitness having a moment, but it's having a significant impact on our health, too.

Research shows that the healthy actions of others rub off on us. A study published in the Journal of Social Sciences found that participants gravitate towards the exercise behaviors of those around them. And a 2016 study published in the journal Obesity found that overweight people tend to lose more weight if they spend time with their fit friends — the more time they spend together, the more weight they lose.

Which makes a pretty strong argument for making your workouts communal. But it’s just one of many reasons why it may be easier (and more enjoyable) to get fit in a pack.

Exercising With a Group Can Take Your Workouts Up a Notch

Whether it’s a group fitness class at the gym or a run in the park with some friends , here are some of the specific benefits you can glean from working out in a group.

Increase your commitment to a fitness routine: “Working out with a crowd carries a plethora of intertwined benefits that include enhancing consistency, duration, motivation , conversation and inspiration,” says Dian Griesel, Ph.D., co-author of TurboCharged and president of public relations firm DGI . “Workouts with others improve consistency because they involve a commitment. ‘No shows’ and cancellations get noticed by others and positive peer pressure can help curtail the urges to skip a workout … or quit.”

One study found that 95 percent of those who started a weight-loss program with friends completed the program, compared to a 76 percent completion rate for those who tackled the program alone. The friend group was also 42 percent more likely to maintain their weight loss.

“For most people, it’s difficult to stay consistent with workout routines, but having a certain group there waiting for you provides you with the motivation and accountability everyone needs to be successful,” says Michael Yabut, Training Manager and National Trainer at TITLE Boxing Club International, LLC, who agrees that members of group fitness programs are less likely to skip workouts, which helps keep them on track.

Push yourself harder: The Köhler Effect is the idea that no one wants to be the weakest link in a group setting. When it comes to fitness, this translates to pushing yourself harder when tasked with working out with people who are fitter than you.

Those who exercised with a more-capable partner increased their plank time by 24 percent.

A study published in the Journal of Sport and Exercise Psychology set out to examine how true the effect really is — having participants perform a series of planks both alone and with a partner (whose performance was manipulated to always be better than the participants). What they found was that working with a partner produced a motivation gain that allowed the participants to hold their planks for a longer period of time. In fact, those who exercised with a more-capable partner increased their plank time by 24 percent.

Other studies confirm that working out with a partner significantly increases time spent exercising. A study by the Society of Behavioral Medicine showed that working with a partner, especially in a team format, improved performance, doubling the workout time of those who exercised alone.

It seems that opting for a group setting for at least a few workouts each week may help you push yourself past the threshold you tend to hit when working out solo — whether that be in time or intensity.

Get a competitive edge: One reason why you may push yourself harder when others are grunting alongside of you is the innate competitive streak in all of us. “Group settings can lead to a positive competitiveness. For instance, wanting to keep up with those around you can make you push yourself harder than you would on your own,” says John Ford , certified exercise physiologist, who runs JKF Fitness & Health (a boutique training company) in New York City. “Seeing what others are capable of doing can inspire you to do more. I’ve personally had this experience: Watching others made me realize I had put some mental barriers up to pushing harder or trying different exercises/routines.”

Researchers at Kansas State University found that people who exercised with someone they thought was better than them increased their workout time and intensity by 200 percent.

Competitive Edge The Right Way to Channel Your Competitive Streak

"We found that when you're performing with someone who you perceive as a little better than you, you tend to give more effort than you normally would alone,” says Brandon Irwin, assistant professor of kinesiology, and principle researcher in the study. “In certain fitness goals, like preparing to run a marathon, consider exercising not only with someone else, but with someone who is that much better. For an extra boost , consider some type of team exercise that involves competition, like playing basketball at a regular time throughout the week."

Capitalize on endorphins: “Group workouts can have a couple of mental advantages over solo workouts. While it’s true that working out releases endorphins (think of all of that talk of a runner’s highs), a group setting can lead to the release of endorphins outside of just physical exertion,” says Ford. “One way is through smiling. Smiling has been shown to increase endorphin levels in studies. So when you’re in a great class or with a great bunch of people working out, that kind of conviviality can really make you feel great outside of just your runner’s high. An added benefit of this mood boost is that when you’re pushing yourself hard and struggling through more difficult parts of your workout you’ll feel better and more energized to complete the exercises.”

A study published in the International Journal of Stress Management found that people who exercised on a stationary bicycle for 30 minutes with a friend said they felt calmer after the workout than those who cycled alone. And it’s also just more fun: Researchers from the University of Southern California found that people who worked out with friends (or a spouse or co-worker) said they enjoyed the exercise more than those who sweat it out alone. Add that to the list of reasons why working out with others may encourage you to make fitness a habit that sticks .

Diversify your workouts: Another benefit of having a plus one at the gym? “Having spotters to make sure that you’re performing an exercise correctly and can do said exercises to failure in a safe manner,” says Ford. “In some instances, having a partner can even help you do exercises that you couldn’t do on your own. Think partner assisted pull-ups.”

There are only so many exercises you a perform alone — throw other person into the mix and you’re able to really get creative. “There are so many fun fitness moves that require having a partner or multiple partners,” adds Ford. “Just trying doing medicine ball toss sit-ups by yourself, it can make you feel really lonely in a hurry. Having multiple people around can really open up a creative catalog of exercises: from partner resisted moves (hey, stop sitting on my back during push-ups!) to relays the options are plentiful and fun.”

Find support — and accountability — in being part of a team: “I believe the best way to workout is in a group setting. For several years, I have taught hundreds of classes, from yoga to boxing, and the best part of it all is the fun that participants have in their workouts,” says Yabut. “It’s an amazing feeling to see [people] do things they never thought they could until it took the person next to them to encourage them to complete that set, rep, mile or round. There’s a bond that is created when a group struggles, sweats, fights, and grinds their way through a tough workout. I focus on building relationships in class because if that happens, I know participants will come back tomorrow.”

“When we work out with other people we can gain a sense of camaraderie, because everyone is there for the same purpose,” agrees Davina Wong, Master Trainer at Club Pilates . “The people you see each week in a group class eventually become your family and want to see you back each week creating accountability.”

There’s a bond that is created when a group struggles, sweats, fights and grinds their way through a tough workout.

And once that group workout is scheduled into your calendar, with other people banking on you showing up, it’s a whole lot harder to hit snooze a second time and roll back over.

“Participants leave happy to have ‘got their workout in,’ to have maintained their record of attendance and relationships, and to have survived another day in a healthy capacity within their fitness community,” McGillivray adds. “They look forward to the next encounter — Whether that encounter is craved due to fitness-related goals or the personal relationships cultivated, it is a win-win scenario for the participant's physical and mental state of health.”

Get external motivation when you’re dragging: Being a part of this type of community can provide a huge boost of motivation beyond the one that comes with the physical benefits of a workout, which can be helpful for those finding it hard to stay committed.

“Motivation improves because group workouts are often filled with encouragement; ‘You can do it!’ cheers and other accolades from others keep the energy and motivation high,” says Griesel. “Inspiration benefits because in a group there is always the one who ‘seems to do it best’ and becomes the ‘reach’ for the group.”

“Working out with other people creates a high level of motivation among one another, especially when someone has a good day,” agrees Wong. “The positive vibes are infectious and spread throughout the class like wildfire, creating a positive attitude and environment for the whole class.”

Think of how much you could benefit from a little encouragement when dragging yourself through those three miles on the treadmill . “When you work out with the right people or in the right class you get uplifted and encouraged to be your best,” says Ford. “All those shouts to do one more, or push to the finish line, plus the high fives and pats on the back for completing sets and accomplishing personal bests create amazing positive feedback loops. And just like with smiling, trigger the release of hormones that make you feel good. All these things can make sure that you stick with your workouts and wellness routine.”

The Potential Drawbacks of Group Exercise

While working out in the company of others can help take your workout to the next level, it is important to be aware of some of the dangers that come with exercising in a group setting.

“One of the biggest issues I’ve noticed is assumed levels of fitness. Many of the moves that are most easily done in classes ( squats , lunges , bent over rows, etc.) require that you already have the proper technique mastered and the core strength and stabilizing muscles to correctly and safely perform the moves,” says Ford. “If you lack any of [this], pushing to do the exercises and allotted reps can often result in depending too heavily on your spine and joints and lead to injuries.”

That’s why some experts recommend sticking to cardio-based classes when challenging yourself in a group or partner setting, since strength training and high-intensity exercises are so personalized and can require individual instruction.

“Having people around to push you can be a great thing, but it can also be a bad thing," warns Ford. "There’s a lot we can do in the moment when trying to keep up with or impress those around us, but it doesn’t mean that we should do those things or were capable of doing those things. Finding the right intensity level of a class and workout buddies is super important."

The competitive spirit can also backfire if it encourages you to push yourself too far beyond your physical abilities. “There may be people who are more competitive than others and may compare themselves to others around them. Nothing is wrong with friendly competition, however, if these people don't listen to their body and understand their limitations, it can lead to injury,” says Wong.

If you’re new to fitness, or to a certain type of workout, it may be best to start solo before jumping into a group setting. “Group settings aren’t always the best teaching settings. It’s hard to get individualized attention to make sure that you’re doing everything correctly,” says Ford. “Even more importantly, the attention to your body to see where you might have weaknesses or imbalances that can lead to health problems down the line. One on one instruction can be great in terms of addressing your body’s specific needs.”

Learning the basics is also important to feeling comfortable in class: One study found working out with others in a mirrored room (like most yoga studios) made untrained women feel self-conscious and uncomfortable.

“I would just emphasize to make sure that you find a group of people or class that fits your personality,” says Ford.

So if you hate bike riding, perhaps a spin class isn’t for you. And if you’ve never boxed before, consider a training session one-on-one before jumping into the ring with a group.

“Remember: It should be a fun time that is enhanced by the people around you,” Ford adds.

And if it can be on the deck of an aircraft carrier in the Hudson River, even better.

TRY THESE FITNESS ROUTINES

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Should You Eat Before or After Working Out?

Proper nutrition is important when exercising, so you may wonder if it’s better to eat before or after a workout. In general, when you should eat may depend on your personal fitness goals, your planned workout, and any underlying health concerns.

Nutrition and exercise are two of the most important factors for your overall health.

What’s more, the two factors affect each other.

Proper nutrition can fuel your exercise and help your body recover and adapt.

However, one common question is whether to eat before or after exercising.

This may be particularly relevant if you exercise first thing in the morning.

Here’s all you need to know about eating before or after working out.

Fasted and Fed Exercise May Produce Different Responses

Studies have shown that your body’s responses to exercise can differ based on whether or not you eat before exercise.

Exercising Fasted Increases Your Body’s Ability to Use Fat for Fuel

Your body’s primary sources of fuel are body fat and carbohydrates.

Fat is stored as triglycerides in fat tissue, while carbs are stored in your muscles and liver as a molecule called glycogen.

Carbs are also available in the form of blood sugar.

Studies show that blood sugar is higher before and during exercise when you eat before working out ( 1 , 2 ).

This makes sense because most of the pre-exercise meals in these studies provided carbs, which the body used for energy during exercise.

When exercising on an empty stomach, more of your body’s energy needs are met by the breakdown of body fat.

A study in 273 participants found that fat burning was higher during fasted exercise, while glucose and insulin levels were higher during non-fasted exercise ( 3 ).

This tradeoff between carbohydrate and fat metabolism is part of your body’s natural ability to function with or without a recent meal ( 4 ).

Exercising Fasted May Not Lead to a Greater Loss of Body Fat

Given that your body burns more fat for energy when it is fasted, it’s tempting to think that this will lead to greater fat loss over time.

One study demonstrated different responses in individuals who exercised in the fasted state, compared to those who ate before exercise ( 5 ).

Specifically, the ability of the muscles to burn fat during exercise and the ability of the body to maintain its blood sugar levels were improved with fasted exercise, but not fed exercise.

Because of this, some scientists believe that your body’s response to exercising fasted would cause more beneficial changes in body fat than exercising after eating ( 6 ).

However, despite some evidence showing potential benefits of exercising fasted, there is no strong evidence that fasted exercise leads to greater weight or fat loss ( 7 ).

Although limited research has been conducted, two studies showed no difference in fat loss between women who exercised fasted and those who exercised after eating ( 8 , 9 ).

Summary Your body’s response to exercise differs based on whether you eat before exercise. Exercising fasted causes your body to use more fat for energy. However, research does not show that this translates to a greater loss of body fat.

Not Eating Before Short-Duration Exercise May Not Affect Performance

Many people who want to perform at their best wonder if exercising fasted will harm their performance.

Some research has tried to answer this question. One analysis examined 23 studies on whether eating before exercise improved performance ( 1 ).

The majority of research showed no difference in performance between those who ate before aerobic exercise lasting less than an hour and those who did not ( 10 , 11 , 12 ).

Other studies examining high-intensity interval training (HIIT) also found no difference in performance between fasted and fed exercise ( 13 , 14 , 15 ).

Although limited information is available for weight training, some research shows that exercising fasted or fed may produce similar results ( 16 ).

One reason why clear benefits of eating before short-duration exercise were not seen in these studies could be due to the body’s own stores of energy.

Your body stores approximately 2,000 calories as glycogen and much more in body fat ( 17 , 18 ).

All that stored energy allows you to exercise even if you have not eaten for hours.

That said, some studies have shown an improvement when carbohydrate-containing meals or supplements were consumed before exercise ( 19 , 20 ).

Eating prior to short-duration exercise does improve performance in some people, and the best choice probably varies based on the individual.

Summary The majority of studies do not show a clear benefit to eating before short-duration aerobic exercise or intermittent exercise like HIIT. However, some studies have shown that eating before exercise improved performance.

Eating Before Long-Duration Exercise May Improve Performance

A large analysis of exercise lasting longer than one hour found that 54% of studies reported better performance when food was consumed before exercise ( 1 ).

Most of the studies showing a benefit of a pre-exercise feeding provided a meal composed primarily of carbs.

Consuming slower-digesting carbs or eating several hours before exercise may benefit long-duration performance.

For endurance athletes, other research has shown benefits of eating a high-carb meal three to four hours before exercise ( 21 ).

There may also be benefits to consuming carbs in the hour before exercise for long-duration events ( 22 ).

Overall, there is stronger evidence in support of the benefits of eating before longer-duration exercise, compared to shorter-duration exercise.

However, some studies showed no benefit of a pre-exercise meal ( 1 ).

Summary While some mixed results have been reported, eating before long-duration exercise is probably beneficial. Recommendations to consume a meal three or more hours before exercise are common, but there may be benefits to eating sooner before exercise.

If You Don’t Eat Before Working Out, You Should Eat Afterwards

While the importance of eating before a workout may vary based on the situation, most scientists agree that it’s beneficial to eat after exercise.

Research shows that some nutrients, particularly protein and carbs, can help your body recover and adapt after exercise.

Eating After Exercise Is Especially Important If You Work Out Fasted

If you eat during the several hours before you work out, the nutrients you ingest may still be present in high concentrations in your blood during and after exercise ( 23 ).

In this case, these nutrients can aid recovery. For example, amino acids can be used to build up proteins, while carbs can replenish your body’s glycogen stores ( 24 ).

However, if you choose to exercise fasted, your body has fueled your workout using its own energy stores. What’s more, limited nutrients are available for recovery.

In this case, it is particularly important that you eat something relatively soon after exercise.

One study examined whether eating a meal containing protein and carbs after fasted exercise led to greater increases in the production of proteins in your body, compared to when no nutrients were consumed ( 25 ).

While there was no difference in how much new protein the body made, eating after exercise did reduce the amount of protein breakdown.

How Soon After Exercise?

While eating after exercise is important, some research has shown that it may not be necessary to eat the second you finish working out.

For example, one study examined how well the carbohydrate stores (glycogen) in muscle were recovered after two hours of cycling ( 26 ).

During one trial, participants began eating immediately after exercise, while they waited two hours before eating in the other trial.

There were no differences in the muscle’s recovery of carbohydrate stores over the eight or 24 hours following exercise, indicating that waiting two hours to eat was not detrimental.

Other research examining the importance of consuming protein immediately after exercise has shown mixed results.

While some studies show that consuming protein immediately after exercise is beneficial for muscular growth, others show no detrimental effects of waiting several hours ( 23 ).

Based on the existing evidence, a reasonable recommendation is to eat as soon as it is feasible after exercise.

Again, eating as soon as possible after exercise may be more important if you do choose to exercise without eating beforehand.

Summary Getting nutrients in the hours around exercise is important. If you don’t eat before exercise, try to eat soon after exercise. Consuming protein can help repair your muscles and other tissues, while carbs can help restore your glycogen stores.

Personal Preference Should Be the Determining Factor

While studies have illuminated the effects of eating or fasting before exercise, the most important factor may be personal preference.

Eating before exercise may be more important for particular groups, such as high-level athletes and those performing long-duration exercise ( 27 ).

However, most active individuals can make great progress when exercising fasted or fed.

Thus, your personal preference about when you eat relative to exercise should play the biggest role in your decision.

For some people, eating soon before exercise can make them feel sluggish or nauseous. Others feel weak and fatigued without having something to eat before working out.

If you exercise in the morning, the duration between when you wake up and when you exercise could impact your choice.

If you head out for a run or to the gym immediately after waking, you may not have time for your food to properly settle before you exercise.

The less time you have between eating and exercise, the smaller the pre-exercise meal should be. This can help prevent feelings of fullness and discomfort during exercise.

As discussed, consuming beneficial nutrients like lean protein and carbs from nutrient-dense foods is important in the hours surrounding exercise.

However, you have the freedom to choose whether to consume these before exercise, after exercise, or both.

Summary Personal preference should determine whether you eat before or after exercise. Eating before exercise may be more important for high-level athletes and those who exercise for long durations, but most can reap the benefits of exercise regardless.

The Bottom Line

Whether or not to eat before exercise is a common dilemma, particularly for those who exercise in the morning soon after waking up.

Although exercising without eating first can increase your body’s ability to use fat for fuel, this does not necessarily translate into greater body fat loss.

In terms of performance, there is limited support for the importance of eating before short-duration exercise. Eating before longer-duration activities may be more beneficial.

Eating before exercise may also be more important for high-level athletes who do not want to risk compromising their performance.

While you don’t have to eat before working out, getting nutrients in the hours around exercise is important.

Therefore, if you don’t eat before you exercise, try to eat soon after you exercise.

Overall, personal preference should be the main factor when deciding whether or not to eat before working out.

How we reviewed this article:

Our experts continually monitor the health and wellness space, and we update our articles when new information becomes available.

Current Version

Jul 3, 2023

Grant Tinsley, Ph.D., CSCS,*D, CISSN

Frank Crooks

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Saturn's ocean moon Enceladus is able to support life − my research team is working out how to detect extraterrestrial cells there

As a planetary scientist and astrobiologist who studies ice grains from Enceladus, I'm interested in whether there is life on this or other icy moons. I also want to understand how scientists like me could detect it.

This article was originally published at  The Conversation.  The publication contributed the article to Space.com's  Expert Voices: Op-Ed & Insights .

Fabian Klenner is a planetary scientist and astrobiologist at the University of Washington (UW). His research focus lies on the exploration of icy moons in the solar system, in particular Saturn's moon Enceladus and Jupiter's moon Europa.

Saturn has 146 confirmed moons – more than any other planet in the solar system – but one called Enceladus stands out. It appears to have the ingredients for life.

From 2004 to 2017, Cassini – a joint mission between NASA , the European Space Agency and the Italian Space Agency – investigated Saturn, its rings and moons. Cassini delivered spectacular findings . Enceladus, only 313 miles (504 kilometers) in diameter, harbors a liquid water ocean beneath its icy crust that spans the entire moon.

Geysers at the moon's south pole shoot gas and ice grains formed from the ocean water into space . 

Related: Life on Enceladus? Europe eyes astrobiology mission to Saturn ocean moon

Though the Cassini engineers didn’t anticipate analyzing ice grains that Enceladus was actively emitting, they did pack a dust analyzer on the spacecraft. This instrument measured the emitted ice grains individually and told researchers about the composition of the subsurface ocean.

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As a planetary scientist and astrobiologist who studies ice grains from Enceladus, I’m interested in whether there is life on this or other icy moons. I also want to understand how scientists like me could detect it. 

Ingredients for life 

Just like Earth ’s oceans, Enceladus’ ocean contains salt , most of which is sodium chloride , commonly known as table salt. The ocean also contains various carbon-based compounds, and it has a process called tidal heating that generates energy within the moon . Liquid water, carbon-based chemistry and energy are all key ingredients for life.

In 2023, I and others scientists found phosphate, another life-supporting compound , in ice grains originating from Enceladus’ ocean. Phosphate, a form of phosphorus, is vital for all life on Earth. It is part of DNA, cell membranes and bones. This was the first time that scientists detected this compound in an extraterrestrial water ocean.

Enceladus’ rocky core likely interacts with the water ocean through hydrothermal vents . These hot, geyserlike structures protrude from the ocean floor. Scientists predict that a similar setting may have been the birthplace of life on Earth .

Detecting potential life

As of now, nobody has ever detected life beyond Earth. But scientists agree that Enceladus is a very promising place to look for life. So, how do we go about looking?

In a paper published in March 2024, my colleagues and I conducted a laboratory test that simulated whether dust analyzer instruments on spacecraft could detect and identify traces of life in the emitted ice grains.

To simulate the detection of ice grains as dust analyzers in space record them, we used a laboratory setup on Earth. Using this setup, we injected a tiny water beam that contained bacterial cells into a vacuum, where the beam disintegrated into droplets. Each droplet contained, in theory, one bacterial cell.

Then, we shot a laser at the individual droplets, which created charged ions from the water and the cell compounds. We measured the charged ions using a technique called mass spectrometry . These measurements helped us predict what dust analyzer instruments on a spacecraft should find if they encountered a bacterial cell contained in an ice grain.

We found these instruments would do a good job identifying cellular material. Instruments designed to analyze single ice grains should be able to identify bacterial cells, even if there is only 0.01% of the constituents of a single cell in an ice grain from an Enceladus-like geyser.

The analyzers could pick up a number of potential signatures from cellular material, including amino acids and fatty acids. Detected amino acids represent either fragments of the cell's proteins or metabolites, which are small molecules participating in chemical reactions within the cell. Fatty acids are fragments of lipids that make up the cell's membranes.

In our experiments, we used a bacteria named Sphingopyxis alaskensis . Cells of this culture are extremely tiny – the same size as cells that might be able to fit into ice grains emitted from Enceladus. In addition to their small size, these cells like cold environments, and they need only a few nutrients to survive and grow, similar to how life adapted to the conditions in Enceladus' ocean would probably be.

The specific dust analyzer on Cassini didn’t have the analytical capabilities to identify cellular material in the ice grains. However, scientists are already designing instruments with much greater capabilities for potential future Enceladus missions. Our experimental results will inform the planning and design of these instruments.

Future missions 

Enceladus is one of the main targets for future missions from NASA and the European Space Agency. In 2022, NASA announced that a mission to Enceladus had the second-highest priority as they picked their next big missions – a Uranus mission had the highest priority.

The European agency recently announced that Enceladus is the top target for its next big mission. This mission would likely include a highly capable dust analyzer for ice grain analysis.

Enceladus isn’t the only moon with a liquid water ocean. Jupiter’s moon Europa also has an ocean that spans the entire moon underneath its icy crust. Ice grains on Europa float up above the surface, and some scientists think Europa may even have geysers like Enceladus that shoot grains into space . Our research will also help study ice grains from Europa.

NASA’s Europa Clipper mission will visit Europa in the coming years. Clipper is scheduled to launch in October 2024 and arrive at Jupiter in April 2030. One of the two mass spectrometers on the spacecraft, the SUrface Dust Analyzer , is designed for single ice grain analysis. 

Our study demonstrates that this instrument will be able to find even tiny fractions of a bacterial cell, if present in only a few emitted ice grains.

With these space agencies' near-future plans and the results of our study, the prospects of upcoming space missions visiting Enceladus or Europa are incredibly exciting. We now know that with current and future instrumentation, scientists should be able to find out whether there is life on any of these moons.

Read the original article at The Conversation.

Join our Space Forums to keep talking space on the latest missions, night sky and more! And if you have a news tip, correction or comment, let us know at: [email protected].

Fabian Klenner is a planetary scientist and astrobiologist at the University of Washington (UW). His research focus lies on the exploration of icy moons in the Solar System, in particular Saturn's moon Enceladus and Jupiter's moon Europa. He is interested in geochemical processes happening on these moons as well as the detection of potential life beyond Earth.

Fabian is an affiliate of NASA's Europa Clipper mission and involved in the planning and design of a potential future Enceladus mission. He is Co-Investigator of BioSigN, an ESA-led experiment to be performed on the International Space Station. Fabian's work is also relevant to the past Cassini mission and he is involved in ESA's CALICO, a potential mission to dwarf planet Ceres. He is member of various learned societies, including his co-leadership of the Ocean Worlds and Icy Moons working group of the German Astrobiology Society.

Before accepting his current position at UW in 2023, he was a Postdoctoral researcher at Freie Universität Berlin, the same university from where he received his Ph.D. in 2021. He studied Earth Sciences at Heidelberg University (M.Sc. and B.Sc.).

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Living Better

Rise and grind working late, volatile hours may lead to depression, illness by 50.

Ronnie Cohen

Working late nights and variable schedules when you're young is linked with poor health and depression at 50, a new study finds. simonkr/Getty Images hide caption

Working late nights and variable schedules when you're young is linked with poor health and depression at 50, a new study finds.

Feeling burned out and looking for reasons to work less? A new study shows that working nights and volatile schedules in young adulthood can leave you vulnerable to depression and poor health in middle age.

The research examined the work schedules and sleep patterns of more than 7,000 Americans interviewed over three decades, from the ages of 22 through 50. To the surprise of the study's author, NYU Silver School of Social Work professor Wen-Jui Han , only one-quarter of the participants worked exclusively traditional daytime hours.

The remainder – three-quarters of the sample of American workers born in the 1960s – worked variable hours. Those with more volatile work schedules, including night hours and rotating shifts, reported less sleep and a greater likelihood of poor health and depression at age 50 than those with more stable schedules and daytime hours.

"Our work now is making us sick and poor," Han said in a Zoom interview. "Work is supposed to allow us to accumulate resources. But, for a lot of people, their work doesn't allow them to do so. They actually become more and more miserable over time."

Han would like her research — published last week in PLOS One — to prompt conversations about ways to "provide resources to support people to have a happy and healthy life when they're physically exhausted and emotionally drained because of their work."

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She was one of those employees. In her 40s, when Han was up for tenure, she worked 16-hour days, taking time off only to eat and sleep, though not sleeping nearly enough. Her doctor warned her that her physical condition appeared more like that of a woman in her 60s.

She was overworking like many young professionals who have embraced hustle culture and work around the clock.

"We can say they voluntarily want to work long hours, but in reality, it's not about voluntarily working long hours," Han said. "They sense that the culture of their work demands that they work long hours, or they may get penalized."

She says the participants in her study who sacrificed sleep to earn a living, suffered depression and poor health, she said. "When our work becomes a daily stressor, these are the kind of health consequences you may expect to see 30 years down the road."

Black men and women and workers with limited educations disproportionately shouldered the burden of night shifts, volatile work schedules and sleep deprivation, the study shows.

White college-educated women with stable daytime work reported an average of six more hours of sleep a week than Black men who had not completed high school and who worked variable hours for most of their lives, Han's study found.

And Black women who did not complete high school and switched from regular daytime hours to volatile employment in their 30s were four times more likely to report poor health than white college-educated men with stable and standard daytime work lives.

The study shows a relationship between working nights and rotating shifts with poor sleep and poor health, but it cannot prove one caused the other. That said, the U.S. Centers for Disease Control and Prevention links insufficient sleep with chronic diseases, such as diabetes, heart disease and obesity, and African Americans are more likely than whites to suffer from these diseases.

How much a person needs to sleep to remain healthy depends upon age, but the American Academy of Sleep Medicine and the Sleep Research Society recommend that adults between 18 and 60 years old get at least seven hours of shut-eye a night.

Dr. Alyson Myers appreciated the new study's focus on the connection between work schedules, sleep and poor health.

The study findings confirmed what she sees in many of her diabetes patients, who often get no more than five hours of sleep after they work night shifts. She counsels them to try to switch to days, and when they do, their health improves, the endocrinologist and professor at the Albert Einstein College of Medicine said.

Prior research has shown that sleep, diet and social habits required to work nights and rotating shifts, can increase the risk of developing diabetes. In 2019, Blacks were twice as likely as whites to die of diabetes , according to the U.S. Department of Health and Human Services.

"Poor sleep is a risk factor for diabetes that very often we do not talk about," said Myers, who was not involved in the study. "One of the things that I have to preach to my patients about is that working nights, and if you get only four or five or less hours of sleep, that's going to increase your risk of diabetes and also worsen your glycemic control."

One patient was angry with her when he followed her advice, switched from working nights to days and as a result had to contend with commute traffic. "But," she said in a Zoom interview, "we actually got better control of his blood sugar when he switched to working the day shift."

About 16% of American workers were employed outside of daytime hours in 2019, according to the U.S. Bureau of Labor Statistics.

Many of the participants in Hans' study who had volatile work schedules tended to have part-time jobs, in some cases multiple part-time jobs. "Unfortunately," Myers said, "the trend for a lot of these people is that they have to work more than one job to survive."

Ronnie Cohen is a San Francisco Bay Area journalist focused on health and social justice issues.

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Black workers’ views and experiences in the U.S. labor force stand out in key ways

There are more than 21 million Black Americans in the U.S. labor force today. Their workforce experiences are varied but stand out from people of other races and ethnicities on several important measures: They are more likely to be employed in certain postal work, transit, health care and security fields; report experiencing more racial discrimination on the job; and place a higher value on diversity, equity and inclusion efforts in the workplace.

For Labor Day, here are facts about Black workers’ labor force experiences and attitudes, drawn from federal data sources and recent Pew Research Center surveys.

Pew Research Center conducted this analysis to understand the views and experiences of Black workers in the United States and how they differ from those of people from other racial or ethnic backgrounds. Findings are based on data from the U.S. Bureau of Labor Statistics, the U.S. Census Bureau and Center surveys. Additional information about each survey and its methodology can be found in the links in the text of this post.

In the Center surveys, references to workers or employed adults include those who are employed part time or full time; are not self-employed; have only one job or have multiple jobs but consider one their primary job; and whose company or organization has 10 or more people.

References to White, Black and Asian adults include those who are not Hispanic and identify as only one race. Hispanics are of any race. Asian American respondents include only English speakers.  

Black Americans make up large shares of workers in certain transit, health and security occupations, according to Bureau of Labor Statistics (BLS) data from 2022, the most recent year available. Black workers account for about 13% of all U.S. workers, including those who work full time, part time and are self-employed. They make up especially large shares of employees in certain occupations, including postal service clerks (40.4%), transit and intercity bus drivers (36.6%), nursing assistants (36.0%), security guards and gambling surveillance officers (34.5%), and home health aides (32.5%).

Black workers make up much smaller shares of farmers, ranchers and other agricultural managers (1.5%). They also tend to be underrepresented in some science, engineering and technology occupations such as veterinarians (2.2%), mechanical engineers (3.6%) and electrical and electronics engineers (6.0%).

A 2021 Center survey found that Black adults see barriers for Black workers in STEM fields, including an unwelcoming professional environment and the need for more mentorship and representation for young people in science, technology, engineering and math.

Black workers generally earn less than U.S. workers overall, according to BLS data from 2022. Among full-time wage and salary workers, the median weekly earnings for Black workers ages 16 and older are $878, compared with $1,059 for all U.S. workers in the same age group. Among workers of other races and ethnicities in the same age group, the median weekly earnings are $823 for Hispanic workers, $1,085 for White workers and $1,401 for Asian workers. And the differences hold when accounting for education level – Black workers earn less than those in other groups even among workers with bachelor’s or advanced degrees.

Household income for Black Americans has lagged behind that for Americans of other races for several decades, according to U.S. Census Bureau data .

The unemployment rate for Black Americans is the highest of any racial or ethnic group and roughly double the rate for the U.S. overall, BLS data shows. In 2022, the unemployment rate for Americans ages 16 and older was 3.7% for men and 3.6% for women, according to BLS annual averages . Among Black Americans, the unemployment rate was 6.3% for men and 6.0% for women. This compared with around 3% each for White and Asian men and women and about 4% each for Hispanic men and women.

Monthly unemployment figures showed a record-low unemployment rate for Black Americans in April of this year, but it has begun to tick back up .

As with gaps in household income, Black Americans have experienced higher unemployment rates than their White counterparts for decades. Researchers have identified a variety of factors causing this trend , including racial discrimination and gaps in education, skills and work experience.

Black workers are the most likely to say they’ve experienced discrimination at work because of their race or ethnicity, according to a February 2023 Center survey of U.S. workers . About four-in-ten Black workers (41%) say they have experienced discrimination or been treated unfairly by an employer in hiring, pay or promotions because of their race or ethnicity. Much smaller shares of Asian (25%), Hispanic (20%) and White (8%) workers say the same.

Among Black workers, 48% of men and 36% of women say they’ve experienced discrimination or unfair treatment by an employer due to their race. There are no gender differences among White and Hispanic workers, and the sample size for Asian workers is too small to analyze men and women separately.

A quarter of U.S. workers say being Black makes it harder to succeed where they work, the February survey shows. Just 8% of U.S. workers say being Black makes it a little or a lot easier to be successful where they work, 50% say it makes it neither easier nor harder, and 17% aren’t sure.

Among Black workers, 51% say that being Black makes it harder to succeed where they work. By comparison, 41% of Asian, 23% of Hispanic and 18% of White workers view being Black as a disadvantage in their workplace. And about four-in-ten or fewer among Asian (39%), Hispanic (29%) and White (7%) workers say that being their own race or ethnicity makes it harder to be successful where they work.

Majorities of Black Americans see racial and ethnic bias as a major problem in hiring and performance evaluations generally, according to a separate Center survey of all U.S. adults conducted in December 2022 . Some 64% of Black adults say that, in hiring generally, bias and unfair treatment based on job applicants’ race or ethnicity is a major problem. This compares with 49% of Asian, 41% of Hispanic and 30% of White adults who view racial and ethnic bias in hiring as a major problem.

When it comes to performance evaluations, 56% of Black adults say that, in general, racial and ethnic bias is a major problem. About four-in-ten Asian or Hispanic adults and 23% of White adults say the same.

Black workers especially value diversity in their workplace, the February survey of workers found. Regardless of how diverse their workplace is, 53% of Black workers say it is extremely or very important to them to work somewhere with a mix of employees of different races and ethnicities. That percentage is larger than the shares of Hispanic, White and Asian workers who say this. And 42% of Black workers say they highly value a workplace with employees of different ages, compared with smaller shares of workers who are Hispanic (33%), Asian (30%) or White (24%).

There is a similar trend in views of workplace accessibility: 62% of Black workers say it is extremely or very important to them to work at a place that is accessible for people with physical disabilities, compared with 51% of Hispanic, 48% of White and 43% of Asian workers.

The vast majority of Black workers say that increasing diversity, equity and inclusion (DEI) at work is a good thing, but a sizable share give their employer low marks in this area, according to the February workers survey .

Around eight-in-ten Black workers (78%) say that focusing on increasing DEI at work is a good thing. Just 1% of Black workers say this is a bad thing, and 20% view it as neither good nor bad. While majorities of Asian (72%) and Hispanic (65%) workers also say that focusing on increasing DEI is a good thing, roughly half (47%) of White workers hold this view. In fact, 21% of White workers say it’s a bad thing.

But when it comes to their own employer’s DEI efforts, 28% of Black workers say their company or organization pays too little attention to increasing DEI – the largest share of any racial or ethnic group. Black workers are also the least likely to say that their company or organization pays too much attention to DEI. Just 3% hold this view, compared with one-in-ten or more among Hispanic (11%), White (16%) and Asian (18%) workers.

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• Business & Workplace
• Discrimination & Prejudice
• Economy & Work
• Racial Bias & Discrimination

A look at Black-owned businesses in the U.S.

8 facts about black americans and the news, black americans’ views on success in the u.s., among black adults, those with higher incomes are most likely to say they are happy, fewer than half of black americans say the news often covers the issues that are important to them, most popular.

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Honey bees experience multiple health stressors out-in-the-field

It's not a single pesticide or virus stressing honey bees, and affecting their health, but exposure to a complex web of multiple interacting stressors encountered while at work pollinating crops, found new research out of York University.

Scientists have been unable to explain increasing colony mortality, even after decades of research examining the role of specific pesticides, parasitic mites, viruses or genetics. This led the research team to wonder if previous studies were missing something by focussing on one stressor at a time.

"Our study is the first to apply systems level or network analyses to honey bee stressors at a massive scale. I think this represents a paradigm shift in the field because we have been so focussed on finding the one big thing, the smoking gun," says corresponding author of the new paper York Faculty of Science Professor Amro Zayed, York Research Chair in Genomics. "But we are finding that bees are exposed to a very complicated network of stressors that change quickly over time and space. It's a level of complexity that we haven't thought about before. To me, that's the big surprise of this study."

The paper, Honey bee stressor networks are complex and dependent on crop and region, published today in Current Biology , takes a much broader look at the interplay of stressors and their effects. The study team also included researchers from the University of British Columbia, Agriculture and Agri-Food Canada, the University of Victoria, the University of Lethbridge, the University of Manitoba, l'Université Laval, the University of Guelph, and the Ontario Beekeepers' Association.

Not all stressors are the same, however. Some stressors are more influential than others -- what researchers call the social media influencers of the bee world -- having an outsized impact on the architecture of a highly complex network and their co-stressors. They also found that most of these influencer stressors are viruses and pesticides that regularly show up in combination with specific other stressors, compounding the negative effects through their interactions.

"Understanding which stressors co-occur and are likely to interact is profoundly important to unravelling how they are impacting the health and mortality of honey bee colonies," says lead author, York Postdoctoral Fellow Sarah French of the Faculty of Science.

"There have been a lot of studies about major pesticides, but in this research, we also saw a lot of minor pesticides that we don't usually think about or study. We also found a lot of viruses that beekeepers don't typically test for or manage. Seeing the influencer stressors interact with all these other stressors, whether it be mites, other pesticides or viruses, was not only interesting, but surprising."

French says the way influencer stressors co-occur with other stressors is similar to the way humans experience co-morbidities, such as when someone is diagnosed with heart disease. They are more likely to also have diabetes or high blood pressure or both, and each one impacts the other. "That's similar to the way we examine bee colonies. We look at everything that's going on in the colony and then compare or amalgamate all the colonies together to look at the broader patterns of what is happening and how everything is related. Two or multiple stressors can really synergize off each other leading to a much greater effect on bee health."

From Québec to British Columbia, honey bee colonies were given the job of pollinating some of Canada's most valuable crops -- apples, canola oil and seed, highbush and lowbush blueberry, soybean, cranberry and corn. The study covered multiple time scales, providing numerous snapshots, rather than the usual single snapshot in time. The research team found that honey bees were exposed to an average of 23 stressors at once that combined to create 307 interactions.

Honey bees are a billion dollar industry. In 2021, honey bees contributed some $7 billion in economic value by pollinating orchards, vegetables, berries and oil seeds like canola, and produced 75 to 90 million pounds of honey. Figuring which stressors would provide the most benefit if managed would go a long way toward developing the right tools to tackle them, something beekeepers are often lacking.

The research is part of the BEECSI: 'OMIC tools for assessing bee health project funded to the tune of $10 million by Genome Canada in 2018 to use genomic tools to develop a new health assessment and diagnosis platform powered by stressor-specific markers.

More research is needed to unravel how the stressors are interacting and impacting honey bee mortality and colony health going forward, says French. "It's really teasing apart which of these compounds might have that relationship and how can we build off this to study those specific relationships."

It can't come soon enough, honey bees are currently facing poor health, colony loss, parasites, pathogens and heightened stressors worldwide. Some beekeepers in this country and the United States face a loss over winter of up to 60 per cent of their colonies.

"Our study suggests some combinations are occurring very frequently," adds Zayed, "and that is relevant because we see them again and again, but we don't know how these combinations affect bee health. It helps to prioritize which experiments we can now take back to the lab and establish how these interactions affect bees."

• Agriculture and Food
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• Origin of life
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• Introduction to genetics

Story Source:

Materials provided by York University . Note: Content may be edited for style and length.

Journal Reference :

• Sarah K. French, Mateus Pepinelli, Ida M. Conflitti, Aidan Jamieson, Heather Higo, Julia Common, Elizabeth M. Walsh, Miriam Bixby, M. Marta Guarna, Stephen F. Pernal, Shelley E. Hoover, Robert W. Currie, Pierre Giovenazzo, Ernesto Guzman-Novoa, Daniel Borges, Leonard J. Foster, Amro Zayed. Honey bee stressor networks are complex and dependent on crop and region . Current Biology , 2024; DOI: 10.1016/j.cub.2024.03.039

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