2 exercise bikers
© University of Turku
Two new studies led by researchers at the University of Illinois have delivered the first clear evidence that the composition of gut bacteria can be changed by exercise alone. Designed to isolate the effects of exercise from other factors that could influence gut bacteria, these dual studies build on an increasing body of evidence affirming the role of exercise in determining the makeup of a person's gut microbiome.

The first study, focusing on a mouse model, took fecal samples from sedentary mice and exercised mice then transplanted that material into germ-free sedentary mice to analyze the effects of the different gut flora.

The results were significant, with the mice that received the exercised gut bacteria displaying an enhanced microbial diversity and a higher volume of butyrate-producing microbes. Butyrate is a short-chain fatty acid (STFA) known to be vital to colon health, energy production and thought to protect against colon cancer.

"We found that the animals that received the exercised microbiota had an attenuated response to a colitis-inducing chemical," says Jacob Allen, co-lead of the research. "There was a reduction in inflammation and an increase in the regenerative molecules that promote a faster recovery."

The second study looked at humans and involved 18 lean and 14 sedentary obese subjects. All the subjects maintained their normal diets but were put on an exercise program consisting of up to an hour of cardiovascular activities, three times a week for six weeks. Each participant's microbiome was sampled before and after the program.

The results of this study were fascinating with notable increases in fecal concentrations for STFAs seen in the lean subjects, but only modest increases seen in the obese subjects. Six weeks after the program was completed, these positive increases had declined following the participants return to a sedentary lifestyle.

"The bottom line is that there are clear differences in how the microbiome of somebody who is obese versus somebody who is lean responds to exercise," says Jeffrey Woods, co-lead on the research. "We have more work to do to determine why that is."

These two studies build on earlier work suggesting a strong correlation between exercise and diversity of healthy gut bacteria. This compelling new discovery, revealing that the effects of exercise could be dependent on obesity status, offers scientists a strangely unexpected new focus of study, and further affirms how mysteriously complex the gut microbiome seems to be.

The first mouse study was published in the journal Gut Microbes, while the second human study was published in the journal Medicine & Science in Sports & Exercise.