Sep 07, 2013 09:47 AM EDT By Staff Reporter, UniversityHerald Reporter

Obesity depends upon the type of bacteria present in the stomach, reveals a recent study.

Researchers induced intestinal microbes from plump and thin people into mice and observed the body mass index change in rodents. Those who were given the bacteria from plump people grew fatter compared to mice who received microbes from thin people.

It's an important player," said Dr. David Relman of Stanford University. "This paper says that diet and microbes are necessary companions in all of this. They literally and figuratively feed each other."

The research was reported in the journal Science.

Vanessa Ridaura, a Washington University graduate student took stomach bacteria from eight people - four pairs of twins that included one obese and one lean sibling. Ridaura then inserted the human bacteria into the intestines of young mice that had been raised germ-free under sterile conditions.

Dr. Jeffrey Gordon, study senior author and director of Washington University's Center of Genome Sciences and Systems Biology, said that the mice who received the stomach bacteria from the obese twins gained more weight and underwent unhealthy metabolic changes, although they didn't consume more than the mice who received bacteria from the lean twins.

In order to determine bacteria's role in helping fight obesity, the researchers put together mice in a cage that received bacteria from both lean and fat individuals. The researchers conducted the experiment to see the effect of swapping intestinal bacteria since mice eat faeces.

They found that when certain bacteria from the lean mice entered the intestines of the fatter mice, their weight and metabolism improved. The improvement was observed only when the fatter mice were fed a low-fat, high-fiber diet. When Ridaura replaced it with the higher-fat, lower-fiber diet, the bacteria from the lean rodents no longer helped the obese animals control their weight.

'In the future, the nutritional value and the effects of food will involve significant considerations of our microbiota - and developing healthy, nutritious food will be done from the inside-out, not just the outside-in,' said Gordon.

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