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Increased exercise benefits gut microbiome

Dear Doctor: I think I remember reading that when you start exercising more, it changes your gut microbiome. How does that work? I thought it’s what you eat and drink that matter the most.

Dear Reader: The way in which physical exercise affects the body has been a subject of interest for thousands of years. Texts dating back to 600 B.C. show that a physician in India prescribed exercise to his ailing patients. Today, we have abundant evidence that exercise affects virtually every facet of bodily function. That starts with the obvious — the muscles — and moves on to include the heart, lungs, liver, kidneys and other organs, and metabolism, endurance, immune response, circulation, hormone levels, gene regulation and blood sugar control.

Now, with the workings of the gut microbiome a new frontier in medical discovery, researchers are asking if exercise plays a role there, as well. The answer appears to be yes. A number of studies conducted in recent years have found that exercise has a beneficial effect on the number, type and diversity of the trillions of microbes that call our guts home. That’s important because these colonies of bacteria, viruses, yeasts and fungi have been shown to be vital to our health, well-being and longevity.

A few years ago, researchers from the University of Illinois asked a group of sedentary women and men to add exercise to their daily routines. They began with 30 minutes of gentle exercise, such as walking three days per week. Over the course of six weeks, the volunteers worked their way up to an hour of vigorous activity, still three times per week. An analysis of stool samples taken at the start and finish of the study found that, even though their diets had not changed, the volunteers’ gut microbiomes had shifted. Each individual’s gut changed in unique ways. However, all of the volunteers had one thing in common: Each person’s gut showed a marked increase in the concentration of short-chain fatty acids. These are the byproducts of fermentation and are produced by the friendly microbes living in the gut.

Short-chain fatty acids serve as a main source of nutrition to the cells of the colon, and they are important to colon health. They also appear to have anti-inflammatory properties. Research has linked short-chain fatty acids to a reduced risk of a range of inflammatory diseases and conditions, including Type 2 diabetes, obesity, heart disease and inflammatory bowel disease. What was particularly interesting about this study was the volunteers were both lean and obese, and the beneficial changes linked to the addition of exercise were seen in both body types.

And, yes, you’re correct that what you eat also plays an important part in optimal gut health. Eating from a wide variety of fiber-rich fresh vegetables, fruits, grains and legumes keeps gut microbes happy. Added sugar and salt have a negative effect on the gut, as do artificial sweeteners. And naturally fermented foods, such as yogurt, kefir, sauerkraut and kombucha, are known to give the gut microbiome a boost.

(Eve Glazier, M.D., MBA, is an internist and associate professor of medicine at UCLA Health. Elizabeth Ko, M.D., is an internist and assistant professor of medicine at UCLA Health.)