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How Does Exercise Affect Our Microbiome? A Gastroenterologist Explains

Will Bulsiewicz, M.D., MSCI
October 17, 2019
Will Bulsiewicz, M.D., MSCI
By Will Bulsiewicz, M.D., MSCI
Dr. Will Bulsiewicz, M.D., MSCI is a gastroenterologist and internationally recognized gut health expert. He completed a bachelor’s degree from Vanderbilt University, a medical degree from Georgetown University, and a master's in clinical investigation from Northwestern University.
Image by Jacob Lund / iStock
October 17, 2019

When it comes to exercise and your health, you'll be hard-pressed to find someone who will dispute that it's good for your health. Study after study has proved the benefits—weight loss, improved mood and cognitive function, stronger bones and muscles (duh!), deeper sleep, and lower risk of heart disease and various types of cancer. Not to mention it can help you discover sex that's off the charts.

The point is exercise yields endless benefits. But have you heard the one about what it can do to improve gut health? Yeah, I'm here to shed some light on why that's true and how you can make it work for you.

What's the microbiome got to do with it?

ICYMI, the power of the microbiome—which are nearly 40 million bacteria strong inside your gut—has been a hot topic lately. Sure, they aid in digestion and, yes, they also help with the absorption of nutrients. Your gut microbiome also promotes glorious bowel movements that are so good you'll want to tell your friends. (But, yeah, it could make for awkward conversation, so maybe keep that one to yourself.)

It also contributes to your metabolism, balances hormones, strengthens the immune system, and helps keep your mind sharp and mood optimistic. There's very little that occurs in the body that does not involve those microscopic microbes inside our colon in some fashion.

All of that is to say that your gut microbiota is basically the director, producer, and star when it comes to the movie featuring an inside look at human health. It's common to think of diet as being the chief determinant of the microbiome because it comes into direct contact with and is processed by gut microbes. After all, the idea that something—like exercise—that never directly enters our intestine could influence our microbial makeup seems much more far-fetched.

But think of it like this: Exercise has tremendous effects on all other aspects of the human body (e.g., brain, heart, muscles, and bones), so it would be crazy to think that exercise wouldn't also support your overall gut health.

Does exercise affect gut health?

Here is what we know: During a 2016 study, researchers discovered that exercise caused dramatic gut microbiota changes1 in mice. They specifically noticed increased microbial diversity, improved intestinal integrity, and more short-chain-fatty-acid (SCFA)-producing microbes.

What's all of that mean? Well, since I know you're a fan of gut health like I am, you can probably guess that it's pretty powerful. Let's unpack it.

Microbial diversity2 is generally considered an indicator of gut health. A more diverse microbiota is more adept at doing what you need it to do. A less diverse microbiota is less capable, and it comes as no surprise that loss of diversity has been associated with the onset of diseases3 such as Crohn's disease, ulcerative colitis, type 1 diabetes, obesity, and even colorectal cancer.

There's a good chance you've heard of "leaky gut" by now. This term is used to describe damage to the gut that reduces intestinal integrity, allowing the leakage or release of bacterial endotoxin, a promoter of inflammation throughout the body. Apply that knowledge to what we already know about exercise improving gut health in mice, and what you’ll discover is that exercise actually reverses leaky gut.

Exercise and short-chain fatty acids (SCFA).

Another aspect of the study was that oh-so-gorgeous boost in SCFA-producing microbes. As you might know, SCFAs are key to gut health. Not only do they reverse leaky gut themselves, but they also have myriad healing effects throughout the body, including an improved immune system and decreased cancer risk.

"Cool," you might be thinking, "but that research was based on an animal study, Dr. B." I feel you but, not to worry, it translates to humans. A 2018 study4 showed that endurance exercise training for 30 to 60 minutes three times a week for six weeks led to the following changes:

  • Increased abundance of SCFA-producing microbes like Clostridiales, Lachnospira, Roseburia, and Faecalibacterium
  • Increased levels of short-chain fatty acids in the stool
  • These changes were correlated with gains in lean mass and loss of body fat

It's remarkable how important SCFAs are for human health and absolutely fascinating that both a healthy, fiber-rich diet and endurance exercise both appear to promote the growth of SCFA-producing microbes. When you have more of these microbes, that means your gut is even more efficient at converting dietary fiber into postbiotic SCFAs. In other words, there is further evidence that when you optimize your lifestyle, the currency of your reward comes in the form of SCFAs.

OK, but are the results long term? 

There is one more finding in the study that I simply can't leave out. After the six-week period of exercising, the participants were asked to return to their sedentary lifestyle. Can you guess what happened? Nearly all of the improvements disappeared. Yeah, so it turns out the adage is true: If you don't use it, you lose it.

Can a healthy gut improve exercise performance?

So, exercise has the ability to strengthen your gut and enhance SCFA release, which is great news. But does it work both ways? Do microbes play any role in exercise performance?

A recent study5 would suggest that, yes, indeed they do.

Nature Medicine5 published the study, noting that researchers identified a specific bacterial strain called Veillonella atypica that was dramatically increased in marathon runners post-marathon. What's cool is that this particular bacteria has the ability to break down lactic acid, which is the acid that builds up in muscles during endurance exercise. Makes sense, right?

When the scientists transferred this particular bacteria into mice, they found that the recipients had improved treadmill run time performance. Yes, they performed better athletically based purely on the presence of this microbe.

 Sure, it's an exciting finding in the world of marathon running, but what I'm most excited about is to see what we find when we study different sports. Is there a special microbe that enhances the start/stop movements in basketball or that promotes muscle recovery after a vigorous workout? My guess is the answer will be yes—but only time will tell.

Now, here's the truth: Exercise is a good idea, regardless of whether it alters your microbiome. But that said, it's nice to know that physical fitness also promotes gut fitness because strong guts translate into better health.

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Will Bulsiewicz, M.D., MSCI author page.
Will Bulsiewicz, M.D., MSCI

Dr. Will Bulsiewicz, M.D., MSCI is a gastroenterologist and internationally recognized gut health expert who wants to help you tap into the incredible healing power that lives inside you—your gut microbiota. His medical training involved 16 years at America's elite institutions. He completed a bachelor’s degree from Vanderbilt University, a medical degree from Georgetown University, and a master's in clinical investigation from Northwestern University. Bulsiewicz was also the chief medical resident at Northwestern and the chief gastroenterology fellow at UNC, and received the highest award given by both his residency and fellowship. He also completed an epidemiology fellowship at UNC's prestigious Gillings School of Global Public Health.