Active Voice: Exercise Training Modifies Our Gut Bacteria

By Jacob Allen, Ph.D., and Jeff Woods, Ph.D., FACSM

Jacob Allen, Ph.D. Jeff Woods, Ph.D., FACSM
Viewpoints presented in SMB commentaries reflect opinions of the authors and do not necessarily represent positions or policies of ACSM.

Jacob M. Allen, Ph.D., was trained as an exercise physiologist with a focus on gut microbial ecology and immunology, earning his Ph.D. in 2017 from the University of Illinois, Urbana-Champaign, Illinois. Jacob is now a postdoctoral scientist in the Microbial Pathogenesis Center within the Research Institute at Nationwide Children’s Hospital in Columbus, Ohio. His research has focused on the effects of environmental triggers, including psychosocial stress, diet and exercise, on the gut microbiota and host-microbiota interactions.

Jeffrey A. Woods, Ph.D., FACSM, earned his Ph.D. from the University of South Carolina, Columbia, South Carolina. He is a past ACSM New Investigator Award recipient and is past chair of the ACSM Research Review Committee. He is currently a professor at the University of Illinois at Urbana-Champaign, while also serving as the associate dean for research and director of the Center on Health, Aging and Disability in the College of Applied Health Sciences. His research has focused on exercise immunology, aging, inflammation and the gut microbiome.

This commentary presents the authors’ views on the topic related to a research article that they published with other colleagues. Their article appears in the April 2018 issue of
Medicine & Science in Sports & Exercise® (MSSE).

Our gut microbiota has emerged as a critical factor regulating our health. Made up of a diverse group of microorganisms, including bacteria, the gut microbiota continually regulates the physiology of its mammalian host. Accordingly, disturbances to the gut microbiota have been associated with a wide variety of chronic health conditions in various tissues— both within and beyond the gastrointestinal tract. Diet, age, sleep and medication usage (among others) can modify the gut microbiota in ways that are impactful to health.

Among these environmental factors, exercise training and fitness status are also emerging as key regulators of the gut microbiota.

Previous animal work has suggested a role of physical activity and exercise in modulating gut microbiota composition during health or in response to deleterious environmental conditions, including high fat diet or experimental diabetes. In people, cross-sectional studies have implicated physical activity and cardiovascular fitness as factors that influence composition and function of our gut microbiota. However, there has been little research examining how exercise training may modulate the human gut microbiota over time. Such a properly controlled study is important considering the high inter-individual variability in our gut microbiota and its responsiveness to potential extraneous factors that may modulate it independently of exercise or physical activity status (e.g., dietary intake).

In our study, as published in the April 2019 issue of MSSE, we demonstrated that six weeks of moderate to vigorous endurance exercise training altered the gut microbiota of 32 previously sedentary lean and obese adults, irrespective of changes in dietary composition or antibiotic usage. These changes were dependent on obesity status and largely were reversed when the participants reverted to six weeks of sedentary behavior. Importantly, exercise resulted in an increase in potentially beneficial short chain fatty acid (SCFA) concentrations and the genes responsible for their production. Exercise-induced changes in butyrate (a prevalent SCFA) and SCFA regulating genes correlated with exercise-induced changes in body composition.

These data support the intriguing possibility that endurance exercise-induced changes in the gut microbiota may mediate health benefits as a result of this form of exercise. These findings signal the need for more extensive investigation into this important biological system.

Our study is significant in that it represents the first human longitudinal exercise trial designed to determine the independent effects of exercise training on the gut microbiome and microbial-derived metabolites. The effects that we observed were dependent upon body mass index and appear to be highly contingent on continued exercise. Further studies are needed to unravel the potential mechanisms behind this response. Determination of the consequences of various training modalities (including resistance training) and durations will further unravel key relationships between exercise and the gut microbiota. Exercise may impact the human gut microbiome in ways that are not yet understood, thus highlighting a novel and exciting field of exploration for exercise scientists.