Researchers at Washington University in St. Louis say the micro-organisms that normally live in the stomach can increase body fat.

The study, summarized in the Proceedings of the National Academy of Sciences, found stomach microbes first break down otherwise indigestible dietary components, effectively increasing the amount of calories we can digest.

These microbes then promote fat storage from the harvested calories by suppressing the gut's production of a protein called fasting-induced adipocyte factor or "Fiaf." Fiaf functions to help keep the gates to fat cells closed.

"Finding that Fiaf is directly manipulated by the gut (stomach) microbiota is intriguing," says senior author Jeffrey Gordon. "It raises the possibility that an individual's predisposition to obesity or leanness may be partly determined by the composition of the microbes living in the gut."

Treatments for obesity that require long-term dietary changes almost always fail. Gordon said his research suggests that derivatives of Fiaf could potentially become therapeutic agents.