Image: Rocky Mountain Laboratories/Wikimedia Commons

Adopting a healthy lifestyle might not seem that hard on the outset. You ate a lot of cheeseburgers and drank a lot of soda, and now you’re going to stop doing that. But a new study in mice suggests that it takes a while for the gut’s bacterial zoo, or microbiome, to adapt to dietary changes. If the results hold in humans, it could mean developing a healthy gut is more than a quick diet fix.

The study, which is published today in the journal Cell Host and Microbe, involved plenty of poop. The researchers first analyzed feces from a group of people who stuck to a calorie-restricted diet that optimized their nutrient intake, and another group of people who ate a so-called American diet without dietary restrictions. Then, the team raised an array of mice whose gut microbiomes included the human fecal bacteria associated with the two diets, fed these mouse models the two different diets, and measured their weight and gut bacterial makeup periodically. In another experiment, the researchers housed calorie-restricted mice and American diet mice together, and again observed how each group’s microbiome responded to either diet.

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The scientists found that poop from the American diet eaters had fewer species of bacteria than poop from calorie-restricted dieters. And even after being moved to a better diet, the mice raised with an American diet-microbiome exhibited lower bacterial diversity. However, the American diet-raised mouse microbiomes responded more strongly to their new healthy diets once they moved into communities with the calorie-restricted mice.

According to Andy Benson, a professor of biotechnology at the University of Nebraska, Lincoln who was not involved with the study, the research is important for showing that different diets have an impact on the configuration of the microbiome. However, he noted a few caveats, like the fact that mice aren’t people. “The more difficult part is how we extrapolate these results to human populations,” he said. He also noted that plenty of other factors determine the microbiome other than just diet.

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Benson worried that folks would get too excited about the fact that housing mice together helped American diet eaters with stunted gut microbiome diversity become more diverse. (In general, more diversity is a good thing for any ecosystem, including the gut, and we probably evolved eating a diet closer to the diversity-promoting calorie-restricted one.)

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The study “definitely generates some thought, and it’s an interesting discussion among scientists. It mortifies me to think of politicians thinking about this,” he said. Plus, he wasn’t sure how this effect would manifest itself in human populations. The paper’s authors use the word “coprophagic,” meaning shit-eating, while discussing how gut bacteria might be passed between mice raised on different diets, and while they did not respond to a request for comment, I doubt people looking to live more healthy will eat the poop of dieting people.

Alessio Fasano, a pediatric gastroenterologist from Massachusetts General Hospital, speculated about what the results might mean for humans. “There’s a well-established [microbial] community dictated by prior dietary practice,” he said. “Even if you make changes in the diet, the microbiome will be hard to modify.”

Fasano emphasized that scientists aren’t so sure if a microbiome lacking diversity is the cause or consequence of gastrointestinal problems. “But when you take a cross section of people who are sick, say with Crohn’s disease, we know the differences in their microbiome are an integral part.”

[Cell Host and Microbe]