Intense Exercise May Alter Gut Bacteria Composition, Study Finds - Video

New research from Edith Cowan University suggests that training intensity may influence the gut microbiome, potentially affecting both health and athletic performance. The study, published in the Journal of the International Society of Sports Nutrition and led by PhD candidate Bronwen Charlesson, explored how different training loads—from high-intensity periods to lighter recovery phases—shape gut bacteria in athletes.

Previous research has shown that athletes tend to have a distinct gut microbiota compared to the general population. They often display greater microbial diversity, higher concentrations of short-chain fatty acids, and differences in the abundance of certain bacterial species. While diet is known to play a role, fitness indicators such as oxygen uptake have also been linked to microbiome variations.

In this study, changes in training load were associated with measurable shifts in gut health markers. During periods of intense training, athletes showed differences in short-chain fatty acid levels and bacterial composition. One possible explanation involves lactate, which rises in the bloodstream during strenuous exercise. Lactate can travel to the gut, where certain bacteria break it down, potentially encouraging the growth of specific microbial strains and altering the overall balance.

The research also found that diet quality declined during low training periods. Although total carbohydrate and fiber intake remained similar, athletes consumed more processed foods, fewer fruits and vegetables, and slightly more alcohol during rest phases. At the same time, gut transit time slowed significantly, which may have further influenced microbial composition.

While scientists are still uncovering how the gut microbiome directly impacts performance, early evidence suggests it may help regulate lactate processing and pH balance—both important for recovery and endurance. Researchers say more studies are needed, but understanding the interaction between training intensity, diet, and gut health could help athletes optimize performance at a microscopic level.

REFERENCE: B. Charlesson, J. Jones, C. Abbiss, P. Peeling, S. Watts, C.T. Christophersen. Training load influences gut microbiome of highly trained rowing athletes. Journal of the International Society of Sports Nutrition, 2025; 22 (1) DOI: 10.1080/15502783.2025.2507952