Could Your Workout Impact Your Gut Health? Yes—And Here’s Why

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Fungi, protozoans, bacteria, nonliving viruses. It might not be pretty, but the human microbiome is a beautiful thing. The approximately 100 trillion bacteria that live in our gut (and, to a lesser degree, our mouths and skin) boost indispensable functions that support metabolism, immune systems, and mental health. Ever-mounting evidence of the powers of the microbiome—some call it “the forgotten organ”—has the health-conscious among us downing probiotic-packed yogurt drinks and investing in prebiotic supplements. Now, it might have us booking into a Spin class.

The link between physical activity and gut flora was noted two years ago, when researchers published a study comparing the national rugby team of Ireland and sedentary men, which found that the elite athletes had healthier guts. But the study did not control for dietary differences among its subjects, which left room for interpretation. The latest research, however, confirms what the rugby study suggested: We can alter our bacterial structure through exercise.

That people who move more have a more diverse microbiome is something that we noticed at my lab several years ago, but we couldn’t prove causality,” says Rob Knight, Ph.D., director of the Center for Microbiome Innovation at U.C. San Diego. “These studies are incredibly exciting.” One, published last week in the journal PLOS One, compared two sets of young mice: those that exercised and those that didn’t. Some of the rodents ate a high-fat diet, others, low fat. Over the course of 12 weeks, the rodents that ran on a wheel, regardless of diet type, experienced an increase in several helpful bacteria—some by as much as 40 percent. The study’s lead author, Sara Campbell, Ph.D., at the Department of Exercise Science and Sport Studies at Rutgers University, points out that she found exercise to be extremely effective at raising levels of butyrate, the bacteria that helps protect against colon cancer. “Exercise might also help you feel less bloated,” she says.

Recent findings out of the University of Colorado Boulder show a similar cause and effect. While the youngest rats in that study had guts that benefited the most as a result of exercise, researchers also found some beneficial changes in the older exercisers. These findings suggest that there is an age of “peak plasticity”—and it’s likely before adulthood—yet the study’s senior author, Monika Fleshner, Ph.D., says the findings could be good news for those of us who are older than Willow Smith. Fleshner’s hunch: Exercise plus prebiotics (commonly nondigestible dietary fibers, often from plants, which help the body’s healthy bacteria flourish) will be the golden ticket. “[It] could have an exponential effect in adults,” she says of the combination. She is midway through a clinical trial testing out her hypothesis.

Perhaps most exciting is a study out of the European University of Madrid that used human subjects. Researchers looked at 104 men and women ages 18 to 45, divided into those who were sedentary and those who exercised three to five hours a week. “Our main goal was to see if exercising regularly, but not professionally, was enough to see changes in the microbiota,” says Mar Larrosa Perez, Ph.D., who led the research. The findings included a four-fold increase in bifidobacterium, which boosts the immune system. Another notable finding: Many of the effects were more pronounced in women. So the next time you consider skipping your morning run, think about what it can do for your form and your gut flora.

That people who move more have a more diverse microbiome is something that we noticed at my lab several years ago, but we couldn’t prove causality,” says Rob Knight, Ph.D., director of the Center for Microbiome Innovation at U.C. San Diego. “These studies are incredibly exciting.” One, published last week in the journal PLOS One, compared two sets of young mice: those that exercised and those that didn’t. Some of the rodents ate a high-fat diet, others, low fat. Over the course of 12 weeks, the rodents that ran on a wheel, regardless of diet type, experienced an increase in several helpful bacteria—some by as much as 40 percent. The study’s lead author, Sara Campbell, Ph.D., at the Department of Exercise Science and Sport Studies at Rutgers University, points out that she found exercise to be extremely effective at raising levels of butyrate, the bacteria that helps protect against colon cancer. “Exercise might also help you feel less bloated,” she says.

Recent findings out of the University of Colorado Boulder show a similar cause and effect. While the youngest rats in that study had guts that benefited the most as a result of exercise, researchers also found some beneficial changes in the older exercisers. These findings suggest that there is an age of “peak plasticity”—and it’s likely before adulthood—yet the study’s senior author, Monika Fleshner, Ph.D., says the findings could be good news for those of us who are older than Willow Smith. Fleshner’s hunch: Exercise plus prebiotics (commonly nondigestible dietary fibers, often from plants, which help the body’s healthy bacteria flourish) will be the golden ticket. “[It] could have an exponential effect in adults,” she says of the combination. She is midway through a clinical trial testing out her hypothesis.

Perhaps most exciting is a study out of the European University of Madrid that used human subjects. Researchers looked at 104 men and women ages 18 to 45, divided into those who were sedentary and those who exercised three to five hours a week. “Our main goal was to see if exercising regularly, but not professionally, was enough to see changes in the microbiota,” says Mar Larrosa Perez, Ph.D., who led the research. The findings included a four-fold increase in bifidobacterium, which boosts the immune system. Another notable finding: Many of the effects were more pronounced in women. So the next time you consider skipping your morning run, think about what it can do for your form and your gut flora.