Does Exercise Alter Gut Microbial Composition? A Systematic Review

Purpose The objective of this systematic review of literature was to evaluate and summarize published research that has investigated the association between exercise and gut microbial composition in mammals. Methods This review was conducted according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines. The databases searched for this review included: PubMed; PubMed Central; Medline; Cumulative Index of Nursing and Allied Health Literature; Web of Science; Commonwealth Agricultural Bureaux Direct; Health Source: Nursing Academic Edition; Clinicaltrials.gov; International Prospective Register of Systematic Reviews (PROSPERO); and the Cochrane Library. Results Twenty-five articles met the inclusion criteria: 17 rodent, one canine, two equine, and five human studies. All studies in rodents and equines included control groups; whereas only one study in humans included a control group. The remaining were cross-sectional or cohort studies. All studies in rodents controlled for dietary intake and one study in humans implemented a 3-d dietary control. Eleven studies assessed voluntary exercise and 13 studies used forced exercise. Diversification within the Firmicutes phylum was consistently observed in exercise groups across studies. There were no consistent trends within Bacteroidetes, Actinobacteria, or Proteobacteria phyla. In general, the potential interactions between exercise and diet composition and their respective influences on the intestinal microbiome were not well characterized. Conclusions Exercise was associated with changes in gut microbial composition, an increase in butyrate producing bacteria and an increase in fecal butyrate concentrations independent of diet in rodents and humans. The overall quality of evidence in the studies in humans was low and the risk of bias was unclear. Future studies with standardized reporting and rigorous dietary control in larger samples are needed to further determine the influence of exercise on gut microbial composition.