A paper appearing in Gut earlier this week reports that exercise can influence the gut microbiome, though others in the field argue that these findings may be correlation rather than causation.
In the study, researchers from University College Cork and elsewhere compared the gut microbiomes of professional rugby players and male controls of similar age and physical size from similar areas.
The rugby players, the authors say, had more diverse gut microbes, and they write that this indicates that exercise has a beneficial effect on the diversity of the gut microbiota. "This is the first report that exercise increases gut microbial diversity in humans," the paper says.
At his Tree of Life blog, Jonathan Eisen argues that the researchers have only shown a correlation between exercise and gut microbe diversity. It could also be, he says, that rugby players follow a different diet or have other, different behaviors that affect the microbiome. He also awards the paper his "Overselling the Microbiome Award."
Despite this criticism, Eisen sees great potential in studying the microbiome, as he tells Alexandra Sifferlin at Time.
"This is what I do. I love this type of work," Eisen, who is a professor at University of California, Davis, tells her. "I just don't want people to overstate what they are doing because I think that's a long-term risk to the field."