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The Weight of the Microbiome

The microbes lurking in the human or mouse gut may influence the weight of that person or mouse. The New York Times points out two new studies that "reflect a growing awareness of the crucial role played by the trillions of bacteria and other microorganisms that live in their own ecosystem in the gut."

In one study, published in Science Translational Medicine, Massachusetts General Hospital's Lee Kaplan and colleagues examine how gastric bypass surgery affects the gut microbiome of a mouse model of obesity. Mice that underwent surgery exhibited changes to their microbiomes, with different levels of Gammaproteobacteria and Verrucomicrobia, while those that underwent a sham operation or sham surgery plus calorie restriction did not. Further, when these post-surgery microbiomes were transferred into other mice, those mice lost weight.

In a separate paper in the Journal of Clinical Endocrinology and Metabolism, a team led by Ruchi Mathur at Cedars-Sinai Medical Center found that people with higher BMIs and body fat also had higher methane and hydrogen levels, as detected by a breath test. The researchers attributed those levels to increased numbers of Methanobrevibacter smithii, which require hydrogen, in their guts. "The people with the highest readings on the breath test were more likely to be heavier and have more body fat, and the researchers suspect that the microbes may be at least partly responsible for their obesity," the Times says.