Healthy Body

You can’t outrun your microbes: how exercise affects your gut

Written by Healthy Living
Writer: Dr. William B. Miller Jr.

Prebiotic and probiotic supplements can help when you push yourself too far.


Millions of Americans are serious about fitness because of its benefits. It is well established that consistent exercise promotes long-term health by lowering blood pressure, improving glucose tolerance, and assisting in weight management. Most people who exercise report an additional positive: improved mental outlook. Recent reports go even further: regular exercise may delay the onset of dementia.

However, those are not the only systems that are affected. Modern research documented many substantial changes that occur with exercise in our gut microbiome, which is being reshaped as a result of the metabolic changes incurred from regular moderate exercise. (The gut microbiome refers to the trillions of bacteria, viruses, and fungi that live in your gut.) Exercise is associated with an increase in gut microbial diversity, which improves your metabolic profile and strengthens your immune system. This shift may be the result of an increase in a particular bacterial strain, bifidobacteria, that is essential for optimum health. These levels tend to decline with age. Exercise provides a boost to that population in our gut.

Although the majority of those who exercise do so moderately, there are increasing numbers of recreational and elite performance athletes who engage in high levels of physical exercise to enhance performance. Extreme exercise is associated with a number of challenges, including a 10 to 20 percent increase in heart size and an increased potential for cardiac arrhythmias. More recent evidence suggests there is also a general immune deficiency associated with prolonged exertion. In fact, it is common for elite athletes at the peak of training to be prone to respiratory illnesses and a range of gastrointestinal symptoms.

Previously, it was surmised the depressed immune function coincident with strenuous exertion and heavy training was a byproduct of dietary deficiencies in protein, carbohydrates, or specific micronutrients. New evidence, however, shows a surprisingly different common denominator. Extreme exercise is associated with gut-related immune deficiency from increased permeability of the intestinal cells that line our gut. This disruption leads to symptoms of nausea, bloating, cramping, pain, diarrhea, and even bleeding. The chronic stress of exercise-induced muscle fatigue and dehydration means the intestinal cells cannot sufficiently counteract and detoxify free radicals being produced by extreme exertion. In these circumstances, some of the less desirable products of ongoing gut microbial metabolism cross the gut lining barrier, a condition known as endotoxemia. As a result, there may be a rise in inflammatory markers in the body and a breakdown of gut integrity. These are pathways toward chronic disease.

Fortunately, there is a way to counteract these negative effects. A number of studies suggest a benefit from prebiotic and probiotic supplements for serious recreational and elite athletes. For example, prebiotics, such as oligofructose-enriched inulin, increase the number of the beneficial bifidobacteria and lactobacillus in the colon. These bacteria protect against pathogens and antioxidants and also stimulate the immune system. A specific byproduct of bifidobacteria metabolism, butyrate, is an essential metabolite in our colon that maintains the energy supply of the body cells lining the colon and protects gut integrity. We now know increasing the proper microbes in your gut enhances the protective effects.

The good news for recreational and endurance athletes is there are convenient ways to prevent common non-muscular complications of strenuous exercise. Certainly, the best advice for your optimum health is exercise in moderation and support those efforts with a balanced and nutritious diet. But, if you insist on pushing toward higher performance levels, part of your exercise regimen should include a daily supplement to boost your gut microbes.


About the writer 
Dr. Bill Miller has been a physician in academic and private practice for more than 30 years, and serves as a scientific advisor for Prebiotin, a prebiotic supplement. He is the author of “The Microcosm Within: Evolution and Extinction in the Hologenome.” For more information, visit themicrocosmwithin.com.

About the author

Healthy Living

Healthy Living is unique in a sea of health magazines that only present information on nutrition and exercise. Published by Akers Media Group, Healthy Living goes much farther by focusing on the four pillars of a true wellness — physical, mental, spiritual and financial health.

Healthy Living promotes a healthy, well-balanced lifestyle with easy-to-read features, try-it-at-home exercise programs, and expert advice from financial planners, mental health professionals, and a variety of other leaders in their respective fields.

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