New evidence that bacteria in large intestine have a role in obesity

Sandrine P. Claus, Jeremy K. Nicholson and colleagues explain that trillions of bacteria live in the large intestine of healthy people, where they help digest food and make certain vitamins. In recent years, however, scientists have realized that these bacteria do more -- they interact with the rest of the body in ways that affect the use of energy and its storage as fat and finely tune the immune system. Claus and Nicholson decided to see how intestinal bacteria might affect the activity of brown fat. The "good" fat that burns calories quickly before they can be stored as fat, brown fat exists in small deposits in the neck area and elsewhere -- not like "white fat" in flab around the waist and buttocks. No one had checked to see if those bacteria could have an effect on brown fat, the researchers noted.

In experiments that compared "germ-free" (GF) mice, which don't have large-intestine bacteria, and regular mice, the scientists uncovered evidence suggesting that the bacteria do influence the activity of brown fat. Brown fat in the GF mice seemed to be more active, burning calories faster than in regular mice. Large-intestine bacteria also seemed to be linked with gender differences in weight. Normal male mice were heavier and fattier than females, but those differences vanished in the GF mice. The research also uncovered major differences in the interactions between males and females and their intestinal bacteria that might help explain why the obesity epidemic is more serious and rapidly developing in women. Those and other findings may point the way toward approaches that kick-up the activity of brown fat in humans to prevent or treat obesity.

The authors acknowledge funding from Nestlé as part of the Imperial College London-Nestlé strategic alliance.