Physical activity is good for the microbiota!
Sports practice improves the composition and functionality of the gut microbiota, but its beneficial effects disappear as soon as you stop training.
The composition and functionality of the intestinal microbiota depend on several environmental and behavioral factors, such as diet, obesity or mode of birth delivery. Leading either an active or a sedentary lifestyle also seems to have an impact on this microbial ecosystem: studies in animals showed that endurance exercise leads to changes in metabolism, immunity and behavior, as well as an increase in short-chain fatty acid production in the intestines*. The impact of endurance exercise in man is still unknown.
Sport and diet
To better understand it, American researchers recruited 32 adults, either thin or obese, leading a sedentary lifestyle. For a period of 6 weeks, the volunteers had to complete 3 weekly endurance training sessions (bike or treadmill), whose duration and intensity increased over time. At the end of this period, they resumed their sedentary habits. The researchers also collected stool samples to analyze the intestinal microbiota before and after the active period, and 6 weeks after resuming sedentary habits. Diet was monitored throughout the study.
A short-term but positive impact
The differences observed in microbiota composition at the beginning of the study between thin and obese individuals had vanished by the end of the 6-week period of physical activity, thus demonstrating the impact of sports practice on the microbiota. Endurance exercise had an impact both on the bacteria composition and functionality, with a greater effect in thin individuals. These effects were associated to favorable changes in body composition (increase in muscle mass, decrease in body fat), but benefits did not persist beyond the physical activity period. The researchers concluded that physical activity leads to changes in the composition and functionality of the intestinal microbiota, and that these changes depend on the body mass index** rather than diet. These changes could prevent some intestinal diseases, such as colorectal cancer or irritable bowel syndrome.
* Short-chain fatty acids are an energy source for tissues, reduce inflammation and improve insulin sensitivity.
** The body mass index (BMI) is defined as the weight (kg) divided by the square of the height (m2); it is used to determine if a person is underweight, normal weight, overweight, or obese.
Allen et al. Exercise Alters Gut Microbiota Composition and Function in Lean and Obese Humans. Medicine & Science in Sports & Exercise. Nov 2017.