How gut bacteria makes us fat, Part 2

Times Staff Writer

Bacteria in the intestines can modify the body’s chemistry to alter the amount of food that becomes stored as fat, according to a finding in mice reported this week that could help in controlling obesity.

A team from the Washington University School of Medicine in St. Louis had reported last month that obese mice -- and humans -- have an unusually high proportion of a family of intestinal bacteria that are exceptionally efficient at breaking down complex sugars in the diet into a form that is readily absorbed. The upshot is that the bacteria make more calories available to the body from a given quantity of food, leading to weight gain.

The same group reported in the current Proceedings of the National Academy of Sciences that the bacteria also play a more direct role, manipulating body chemistry to increase the amount of food stored as fat.


Dr. Jeffrey I. Gordon and his colleagues fed both microbe-free and normal mice a “Western” diet, high in fat and sugars. The sterile mice stayed lean, while those with intestinal bacteria gained weight and eventually became obese.

Closer inspection revealed that the bacteria were interfering with two intestinal processes.

The bacteria suppressed production of a hormone called fasting-induced adipose factor, thereby stimulating the rodents’ bodies to store more of the available calories in the form of fat.

The bacteria also suppressed production of another enzyme, called adenosine monophosphate-activated protein kinase, which is used by the body to burn stored fat for energy. Lower levels of the enzyme make weight loss more difficult.

The net effect is that the bacteria not only make more calories available to the body, they encourage the body to store that energy as fat and keep the fat on.

It is unlikely that any manipulation of bacterial levels or composition could produce weight loss, experts said, but drugs that block this activity might.