The battle of the bulge can be frustrating, with small victories overshadowed by major losses.

But research may bring some comfort. Bacteria, and not just gluttony or laziness, may be to blame. The bacteria can actually make genes generate fat.

Scientists have believed that microscopic organisms in the gut, microbiota, might play a crucial role in gaining weight but were never able to prove it.

Groundbreaking research by a Chinese scientist has revealed a precise link.

In 2004, microbiologist Jeffrey Gordon from Washington University School of Medicine in St. Louis, Missouri, and his colleagues first showed a general link between obesity and gut microbiota in mice.

Another leading researcher said that while a link was believed to exist, proving it was another matter.

"The list of diseases that they may play a role in is just growing and growing," Lita Proctor, director of the US National Institutes of Health's Human Microbiome Project in Bethesda, Maryland said.

"But the problem is that we're only able to look at associations and aren't yet able to conduct cause-and-effect studies."

A research team led by Zhao Liping, a professor of microbiology and associate dean at the School of Life Sciences and Biotechnology at Shanghai Jiao Tong University, pointed out the precise link between a particular kind of bacteria and obesity.

The paper was published on Dec 13 in the journal of the International Society for Microbial Ecology.

It showed that a pathogen, or infectious agent, isolated from the gut of an obese human induced obesity and insulin resistance in germ-free mice.

In the clinical study, researchers found an excessive growth of endotoxin-producing bacteria, accounting for 35 percent of the gut bacteria, in an obese patient whose initial weight was 175 kg.

After an intervention with specialized nutritional formula, the bacteria decreased to non-detectable amounts and the patient lost 51.4kg.

It provided the key piece of evidence.