Intestinal Bacteria May Explain Obesity

ST. LOUIS (AP) _ The microorganisms that live in your gut could explain one of the sources of obesity, says a new study from researchers at Washington University.

Bacteria live throughout the body, but some intestinal bacteria appear to be better than others at helping their hosts turn food into energy, say researchers Buck S. Samuel and Dr. Jeffrey I. Gordon.

They believe changing the mix of bacteria in the intestine could influence how much people weigh.

Bacteria and archaea, another kind of single-celled organism, are common in the human intestine. Researchers are discovering that together, they help their human hosts extract calories and nutrients from food.

"We know very little about who they are and what they do,'' said Dr. Martin J. Blaser, chair of medicine at New York University.

Samuel decided to investigate that question by inoculating identical mice with different microbes, or a combination of two of the single-celled organisms.

The researchers found mice whose guts were inoculated with just the bacterium Beta thetaiotaomicron (B. theta) could process rodent food better than mice that were given no bacteria.

A second group of mice were inoculated with a combination of B. theta and an archaeon called Methanobrevibacter smithii (M. smithii). Those rodents could extract many more calories from the same amount of food, but they stored the extra energy as excess fat.

The researchers haven't yet concluded whether obese people have more M. smithii in their intestines. But Blaser said he believes scientists could eventually help control human nutrition by manipulating the types of microbes living in the gut.

The results of the study will be published online this week in the Proceedings of the National Academy of Sciences.

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