Gut Bacteria Might Be Making People Fat

Nov. 12 -- WEDNESDAY, Nov. 11 (HealthDay News) -- Eating a Westernized diet with lots of sugar and carbohydrates caused almost instantaneous changes in the gut flora of mice -- changes that caused the mice to become obese, researchers have found.

These shifts in the microbial environment, reported in the Nov. 11 edition of Science Translational Medicine, might mean that experts should look more closely at the billions of microorganisms residing in human guts to better understand and perhaps even treat the epidemic of obesity plaguing the modern world.

"Although how much you eat and how much you exercise are dominant drivers of your energy balance, it's possible that microbial communities and how they work also comprise a factor that determines your risk for obesity or risk for malnutrition," said study senior author Dr. Jeffrey I. Gordon, director of the Center for Genome Sciences at Washington University School of Medicine in St. Louis.

The researchers plan to use the mouse model, or "humanized" mouse, to further study the diverse organisms that reside in people's guts and how their presence might effect their hosts' health.

"There are 10 times more microbial cells associated with adult human bodies than there are human cells, so we are 90 percent microbial and 10 percent human," Gordon said. The bacteria can help people digest and absorb food that might otherwise be indigestible.

But the denizens of the digestive system are hard to study, given the complex environmental, genetic and cultural factors that affect digestion and obesity.

To devise a better way to study these microorganisms, Gordon and his fellow researchers transplanted microbes from human feces into mice that, courtesy of genetic manipulation, had no gut microorganisms of their own.

"When we switched these humanized animals [from a low-fat] to a junk-food diet, high in fat with lots of simple sugars, the structure of the microbial community changed dramatically and very rapidly, not only in terms of who's there or which species but the proportional representation of species changed very abruptly within 24 hours," Gordon explained. "These mice also became obese on Western diets."