PhD candidate Ms. Bronwen Charlesson examined how different training loads, ranging from high intensity to lighter periods, affect athletes’ gut health. Her goal was to better understand how changes in the gut microbiome might support improved health, well-being, and athletic performance.

Athletes and the Gut Microbiome

“Based on previous research, it appears that athletes have a different gut microbiota when compared with the general population. This includes greater total short chain fatty acid concentrations, alpha diversity, an increased abundance of some bacteria and a lower abundance of others,” she said.

Athletes’ gut bacteria often differ from those of non-athletes. While diet likely plays a role in these differences, Ms. Charlesson noted that fitness indicators such as oxygen uptake have also been linked to variations in the microbiome.

In the new research, training load itself was associated with measurable shifts in gut health markers. Athletes showed differences in short-chain fatty acid levels and in the presence of certain bacterial species depending on how hard they were training.

Intense Exercise, Lactate, and Gut Bacteria

Although it was not directly tested in this study, one possible explanation involves lactate, which increases in the bloodstream during intense exercise. Lactate produced by working muscles travels to the gut, where it is broken down. This process may encourage the growth of certain bacteria, potentially reshaping the microbial balance.

Diet Quality and Low Training Periods

The study also found that diet patterns changed when training demands dropped.

“During low training load times, or periods of rest, athletes are often more relaxed about their diets, in this study we saw no change in total carbohydrate or fiber intake during period of rest but we did observe a decline in the diet quality of food eaten. This decline was related to increases in processed fast foods, decreases in fresh fruit and vegetables and a moderate increase in alcohol intake. These changes did impact the composition of the gut microbiome.

“Another observation made during the research was the significant slowing of gut transit times in athletes during low training loads. That slowing of transit time during the low training load appears to also be impacting the gut microbiome for an athlete.”

Even though overall carbohydrate and fiber intake remained steady, the quality of food choices declined during rest periods. At the same time, digestion slowed, which may have further influenced the composition of gut bacteria.

What It Means for Athletic Performance

Researchers still do not fully understand how the gut microbiome affects athletic performance, but early clues are promising. The gut may help process lactate and regulate pH levels, both of which can influence physical output and recovery.

Ms. Charlesson emphasized that more research is needed to clarify how training intensity, diet quality, and gut transit time interact. A deeper understanding of these factors could help athletes fine tune their routines to support both gut health and performance.