Overweight? It Could Be Your Intestinal Bacteria

Dec. 20, 2006— -- Overweight individuals may now have a new factor to blame for their excess weight -- the germs living inside their guts.

The trillions of microbes living inside our intestines may play a role in the differences in body weight among people, suggests a new study published in this week's issue of the journal Nature.

"Groundbreaking work like this that opens up a novel hypothesis is important," said Dr. Randy Seeley, associate director of the obesity research center at University of Cincinnati.

Researchers found that the bacteria in the guts of obese mice are better at extracting energy from food than gut bacteria in lean mice. In short, the fat mice take away more calories from their food.

Moreover, when the bacteria from the guts of obese mice were transplanted to slimmer, germ-free mice, these germ-free mice got fatter.

"There is a tremendous battle waged by scientists from many different backgrounds to try to understand this worldwide epidemic of obesity," said Dr. Jeffrey Gordon, director of the genome science center at Washington University in St. Louis and senior author of the study. "We want people to consider the microbial community as a potential factor."

"We had a question about the role our gut microbes play in human health," said Gordon. "Because we never dine alone."

Humans have had a long-standing, evolutionary relationship with bacteria and other microorganisms living in the gut. Many of these bacteria are necessary for well-being because they help us digest food particles that we cannot digest on our own.

"These trillions of microbes provide us with different sets of attributes that are important," said Gordon. "For example, the sugars known as polysaccharides in grains and vegetables have complex structures. Our microbial organisms have the tools to break down these structures and help us extract energy."

The differences in the identity of these gut bacteria may be a clue into why some people are obese and others are lean.

"One interesting idea [from this research] is that our gut microbes may be responding to changes in our body weight," said Seeley.