In a study of 39 participants who were equal in age, body- mass index (BMI), and diet, researchers found that differences in cardiorespiratory fitness were associated with differences in microbiome composition.1,2 The participants with the highest levels of cardiorespiratory fitness demonstrated greater gut microbial diversity, with a higher abundance of butyrate- producing bacteria, than the less fit participants. This suggests that physical activity can independently improve gut health in healthy adults. However, the participants in this study all fell within the “normal” BMI range, and a separate study from 2018 suggested that these results couldn’t be extrapolated to individuals with overweight and obesity. The 2018 study evaluated the impact of a six-week exercise intervention on the gut microbial composition, function, and metabolic output of a previously sedentary group of 32 lean or obese participants (18 lean participants, 14 obese participants).3 The supervised exercise intervention began with 30 minutes of endurance training three days per week, which progressed to 60 minutes. Afterward, the participants were instructed to return to their sedentary lifestyle for six weeks (washout period). After analyzing the participants’ fecal samples that were collected during pre-intervention, post-intervention, and post-washout periods, the researchers found that the fecal samples of the lean individuals showed an increased concentration of short-chain fatty acids (SCFA) immediately after the six-week exercise intervention, while the samples from the participants with obesity did not reflect the same increase. Additionally, the increased SCFA production in the lean participants decreased to pre-intervention levels after the six-week washout period, suggesting that exercise-associated gut microbial benefits persist only as long as physical activity is maintained.

REFERENCES

1. Estaki M, Pither J, Baumeister P, et al. Cardiorespiratory fitness as a predictor of intestinal microbial diversity and distinct metagenomic functions. Microbiome. 2016 Dec;4(1):42.

2. Monda V, Villano I, Messina A, et al. Exercise modifies the gut microbiota with positive health effects. Oxidative medicine and cellular longevity. 2017.

3. Allen JM, Mailing LJ, Niemiro GM, et al. Exercise alters gut microbiota composition and

function in lean and obese humans. Med Sci Sports Exerc. 2018 Apr 1;50(4):747–757. NHR