Gut bacteria may be linked to obesity

The guts of obese people are teeming with a distinctive mix of bacteria that seems to make them prone to gaining weight, a startling discovery that could lead to new ways to fight the obesity epidemic, researchers reported Wednesday today.

Obese people have more gut microbes that are especially efficient at extracting calories from food, the researchers said, and the proportion of these super-digesting organisms ebbs as they lose weight. Moreover, when the scientists transplanted gut bugs from obese mice into lean mice, the thin animals start getting fat, providing more support for the provocative theory that the bacteria play an important role in regulating weight.

“There appears to be a link between obesity and the type of bugs in your gut,” said Jeffrey Gordon of Washington University School of Medicine in St. Louis, who led the series of experiments being published in today’s issue of the journal Nature.

Gordon and his colleagues stressed that more work is needed to explore the findings. And they cautioned against trying to manipulate “gut flora” with antibiotics or microbe-containing “probiotic” pills sold in health food stores. But if the findings are confirmed and better understood, they could lead to profound new insights into one of the world’s biggest health problems, they said.

The findings produced enthusiasm and caution from other researchers. Some praised the work for possibly offering a long-sought alternative explanation for the obesity epidemic.

“This is very exciting,” said Barbara Corkey, an obesity researcher at Boston University. “We don’t know why the obesity epidemic is happening. People say it’s because of gluttony and sloth. I think there must be something else.”

Others suspect that if gut microbes do play a role, it’s probably relatively minor.

“This is extremely interesting,” said Hans-Rudolf Berthoud of the Pennington Biomedical Research Center in Baton Rouge, La. “But lifestyle and the environment are still the major factors in the obesity epidemic.”

Gordon’s team first compared the gut flora of 12 obese people to lean subjects. The obese tended to have significantly greater proportion of one of the two main types of bacteria found in the gut, known as Firmicutes, than the other, known as Bacteroidetes.

Next, the researchers spent a year meticulously measuring the gut flora of the obese volunteers as they tried to lose weight by eating low-calorie diets. As they lost weight, the proportion of Firmicutes fell and the proportion of Bacteroidetes rose, the researchers found.

When the researchers conducted detailed molecular analyses of the two types of bacteria in the laboratory, they discovered the Firmicutes were much better at extracting calories from food.