We already know that exercise benefits both body and mind at every stage of life, but new findings suggest it may also be working in a less visible area — your gut. This adds to the growing evidence that the gut microbiome plays a key role in overall health.
A team at Edith Cowan University (ECU) discovered that it’s not just the act of exercising, but also how intensely you work out, that can shift the balance of microbes in the digestive system, creating conditions that support better health.
Researcher Bronwen Charlesson explained that past studies suggest athletes have gut microbiota that differ from the general population. These differences include higher overall levels of short-chain fatty acids, greater microbial diversity, and variations in the abundance of certain bacteria.
Training Intensity and Rowers’ Gut Microbiome
Importantly, you don’t have to be an elite athlete to gain potential benefits. Still, this study examined 23 high-performance rowers, whose gut microbiomes were analyzed both during a period of intense training leading up to a national competition and again during their off-season, when their workouts were far less demanding. Training during the high-intensity phase was nearly 150% more vigorous and lasted about 130% longer compared to the lighter period.
The results showed that during the heavy training phase, the rowers consistently had elevated levels of short-chain fatty acids (SCFAs) — especially butyrate and propionate. These compounds support gut lining integrity, help reduce inflammation, and play a role in energy metabolism. Specifically, butyrate levels climbed from 64 mmol/L at rest to 105 mmol/L in intense training, while propionate rose from 91 mmol/L to 121 mmol/L.
The researchers also observed that athletes’ digestion accelerated during this period. Nearly all participants (92%) reported daily bowel movements when training intensely, compared with less frequent patterns in the off-season.
Training Boosts Bacteroidota, Alters Gut Balance
“During intense training, Bacteroidota—microbes that help digest complex carbs—increased, while the Firmicutes-to-Bacteroidota ratio dropped. Higher ratios are linked with weight gain and poorer metabolism, while lower ratios (more Bacteroidota) are tied to leanness and healthier outcomes.” Still, researchers note this is an emerging field and not yet fully understood.
One possible explanation involves lactate, which builds up in muscles during intense workouts and travels to the gut. Certain microbes consume lactate and convert it into beneficial short-chain fatty acids (SCFAs) like butyrate and propionate. In doing so, they also reduce gut acidity, creating an environment that supports other microbes. In effect, training harder may “feed” the microbiome in ways that boost gut and overall health.
By contrast, in the off-season, the rowers’ overall intake of carbs, protein, and fiber didn’t change much, but diet quality declined—fewer fruits and vegetables, more takeaway meals, and slightly more alcohol. Their Athlete Diet Index scores reflected this drop, falling from 55 to 49.
Intense Training Alters Digestion and Microbial Balance
Digestive changes followed: bowel movements became less frequent (only about half maintained a 24-hour cycle), SCFA levels decreased, and Bacteroides—a key genus that breaks down carbs and fiber into SCFAs that stimulate gut motility—dropped in abundance. Although overall microbial diversity increased, many of the microbes that flourished weren’t necessarily beneficial.
In short, during lighter training phases, the gut appeared less metabolically active and potentially less supportive of good health.
As researcher Bronwen Charlesson explained: “When training loads are low, athletes often relax their diets. While total carb and fiber intake stayed the same, food quality declined—with more processed fast foods, fewer fresh fruits and vegetables, and moderate increases in alcohol. These changes clearly impacted the gut microbiome.”
She added: “We also observed a notable slowing of gut transit times in low training periods, which in turn seemed to affect the microbiome itself.”
Untangling the Effects of Diet vs. Exercise on the Gut
Diet and alcohol strongly influence the gut, and athletes ate less healthily when training eased. Still, since benefits aligned with harder workouts, faster gut transit, and lactate use, the study suggests exercise itself can directly shape the microbiome.
So, what does this mean for non-athletes? From weightlifting to brisk walks, vigorous movement may boost gut health. While more research is needed, this study suggests workout intensity plays a key role—adding another reason to stay active.
The research was published in the Journal of the International Society of Sports Nutrition.
Read the original article on: New Atlas
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