Diet, lack of exercise and heredity have all been implicated in the epidemic of obesity sweeping the world. Now, scientists have a new culprit to add to the list: the bugs inside us.
The human gut is home to trillions of mostly helpful microbes that play vital, varying, and often undocumented, roles in digesting the food we eat. Some — to the detriment of waistlines the world over — are better at it than others.
New research, reported in a British journal, suggests that two of the most common classes of digestive bacteria play a previously unsuspected role in determining whether a person gains weight — and how much — from a given quantity of food.
Scientists say obese people have a preponderance of microbes in their digestive tract that are very efficient at extracting energy from food, energy that the body can then burn, or tuck away in fat cells. Lean people have more of a preponderance of microbes that are less efficient at extracting energy, so the undigested portion of food passes through the body without accumulating as fat.
"Our findings suggest that obesity has a microbial component,” says Jeffrey Gordon, the director of the Centre for Genomic Sciences at Washington University. "Microbes in our gut are part of the equation that affects a person’s predisposition to obesity.” And that, Gordon says, opens the door to the possibility that efforts to control obesity might someday focus, in part, on changing the composition of bacteria in the gut. The latest research doesn’t contradict evidence that people who eat a lot and exercise little are more likely to gain weight. Nor does it discount the role of heredity. Since 1994, scientists have found about 50 genes that play a role in obesity.