How your gut bacteria may affect your weight and health

Two articles in recent weeks detailed some new and significant findings about the human gut microbiome.  First from NPR:

Moving to the U.S. can seriously mess with immigrants' microbiomes, according to a new study that tracked the digestive health of refugees coming to Minnesota from Southeast Asia. "We found that when people come to the U.S.A., they almost immediately begin losing some of their native microbes," says Dan Knights, a quantitative biologist at the University of Minnesota and the study's senior author. Some of the strains they lose are ones that help them break down and glean nutrients from fibers found in Southeast Asian staples like wild greens, coconut and tamarind...

Among that group of 19 refugees, researchers noticed that a Western bacteria strain called Bacteroides began to displace the non-Western strain Prevotella within their first six to nine months in the U.S. But they lost more microbes than they gained — "so the diversity in their microbial communities decreased," Knights says. "And some of the Prevotella bacteria they lost were the ones that helped them digest fiber from plants and greens."

Some of the bacteria in our guts feed, and survive, on particular fibers found in grains and greens — and die off when they don't get enough. But changes in diet didn't explain all — or even most — of the change in immigrants' microbiomes. "It could be that other factors, like exposure to different medications, especially antibiotics or changes in the quality of water they're drinking, are also affecting their microbiomes...

"In speaking with community members, we also realized that for them, the biggest concern was obesity," says Vangay. "Because they had observed in themselves and their relatives and friends that when they moved to the U.S., they gained a lot of weight. And in some cases, they hadn't really changed too much about their diet."

Fascinating.  Now this from Harvard Magazine:

A. Sloan Devlin, an assistant professor at Harvard Medical School, and her team have discovered that altering a single gene in a single type of bacteria can even change the metabolism of the host organism...

During the 32-day study, the mice that could not process bile, for instance, had more fat in the liver and gained weight much more slowly than the other group. They also used proportionately less fat and more carbohydrate for energy...

“It’s a bacterium,” she points out, “and a single enzyme in a bacterium, that’s causing a change in whether the host is using fats versus carbohydrates.”

Control of body weight used to be conceptually so simple: calories in minus calories expended.  Now it appears to be much more complex than that.

Related: Fecal transplant to treat C. difficile colitis.