Gastrointestinal bacteria more important than calorie intake to obesity

Metagenomics of Obesity

We now know that 90 percent of the cells in “our” bodies aren’t ours at all. Instead, they belong mainly to the bacteria in our gastrointestinal tract. Consequently, the overwhelming majority of “our” genes actually belong to those microbes. But could microbes play a role in obesity?

A recent study by Jeffrey Gordon of Washington University has found alink between gut microbes and obesity. The research group assigned 12 obese volunteers to low calorie diets. Over the course of a year they put sample from the GI tract through metagenomic analysis, and focused on members of two major bacterial groups, Firmicutes and Bacteriodes, which are predominant in the human and mouse gut.
The obese people began with more Firmicutes and fewer Bacteriodes than the lean people they were compared to. However, as the diets wore on, the proportion shifted toward Bacteriodes – more like the lean people.

In a second study, Gordon found a similar preponderance of Firmicutes in genetically obese mice, and reported that their gut microbes were "more effective at releasing calories from food during digestion" than microbes in non-obese mice. Furthermore, when the researchers raised mice without any gut microbes, and then gave those mice microbes from the obese mice, the animals got fat.

In other words, gut bacteria could be more important to obesity than calorie intake.

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