Exercise changes gut microbial composition independent of diet, team reports -- ScienceDailyIn the mouse study, changes in the microbiota of recipient mice mirrored those in the donor mice, with clear differences between those receiving microbes from exercised and sedentary mice. "That proved to us that the transplant worked," Woods said. Recipients of the exercised mouse microbiota also had a higher proportion of microbes that produce butyrate, a short-chain fatty acid that promotes healthy intestinal cells, reduces inflammation and generates energy for the host. They also appeared to be more resistant to experimental ulcerative colitis, an inflammatory bowel disease. "We found that the animals that received the exercised microbiota had an attenuated response to a colitis-inducing chemical," Allen said. "There was a reduction in inflammation and an increase in the regenerative molecules that promote a faster recovery." In the human study, the team recruited 18 lean and 14 obese sedentary adults, sampled their gut microbiomes, and started them on an exercise program during which they performed supervised cardiovascular exercise for 30-60 minutes three times a week for six weeks. The researchers sampled participants' gut microbiomes again at the end of the exercise program and after another six weeks of sedentary behavior. Participants maintained their usual diets throughout the course of the study. Fecal concentrations of SCFAs, in particular butyrate, went up in the human gut as a result of exercise. These levels declined again after the participants reverted to a sedentary lifestyle. Genetic tests of the microbiota confirmed that this corresponded to changes in the proportion of microbes that produce butyrate and other SCFAs. The most dramatic increases were seen in lean participants, who had significantly lower levels of SCFA-producing microbes in their guts to begin with. Obese participants saw only modest increases in the proportion of SCFA-producing microbes. The ratios of different microbes in the gut also differed between lean and obese participants at every stage of the study, the researchers said. "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," Woods said. "We have more work to do to determine why that is."