Previously inactive people who exercise for at least 30 minutes a day three times a week experience increased levels of gut bacteria that produce butyrate, a study found.
Butyrate is an anti-inflammatory acid that has been linked to protection against bowel cancer, as well as weight loss and stronger immunity.
The same findings were previously found in mice, who became less likely to develop the inflammatory bowel disease ulcerative colitis if they were active.
Lead author Professor Jeffrey Woods from the University of Illinois, said: 'These are the first studies to show that exercise can have an effect on your gut independent of diet or other factors.'
Yet, the catch is exercise's positive impact on gut bacteria is reversed if people revert to being inactive.
How the research was carried out
The researchers analyzed 18 lean and 11 obese women.
All of the study's participants were previously sedentary before undergoing six weeks of endurance-based activity for three days a week that progressed from 30 minutes of moderate exercise a day to one hour of vigorous activity.
The participants then went back to a sedentary lifestyle for six weeks.
Their diets were consistent throughout the study.
Fecal samples were collected before and after the participants became active.
Results reveal exercise changes gut bacteria, which is largely reversed if people revert to being inactive.
In particular, species that produce an anti-inflammatory acid known as butyrate increase, which has previously been linked to bowel-cancer protection, weight loss and stronger immunity.
For unclear reasons, the findings are greater in lean people than those who are obese.
The same findings also previously occurred in mice, who become less likely to develop the inflammatory bowel condition ulcerative colitis if they exercise.
Professor Woods said: 'These are the first studies to show that exercise can have an effect on your gut independent of diet or other factors.
'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. We have more work to do to determine why that is.'
The current study's results were published in the journal Medicine & Science in Sports & Exercise.