Gastric bypass surgery changes gut microbes

illustration of different weight loss surgeries

Two types of weight loss surgeries, Roux-en-Y gastric bypass (center) and vertical banded gastroplasty (right), change the mix of microbes in women’s intestines. Mice with microbes transplanted from the women who had surgeries gained less weight than did mice that got bacteria from obese women. 

 Tremaroli and Karlsson et al./Cell Metabolism 2015

Weight loss surgery causes bacteria in the intestines to extract fewer calories from food, a new study suggests.

Changes to the gut microbiome last at least nine years after Roux-en-Y gastric bypass or gastric banding surgery, researchers report August 4 in Cell Metabolism. Groups of women who had either gastric bypass or an operation called vertical banded gastroplasty both had long-lasting changes to their microbiomes regardless of how much weight they lost.

Researchers transplanted bacteria from obese women and from women who had the surgeries into mice raised without gut microbes. Mice with gut bacteria from the surgery groups gained less body fat than did rodents with microbes transplanted from obese women.

Gastric bypass in particular switched the metabolism of microbes so that they burned fewer carbohydrates and more fat, the scientists write. 

Tina Hesman Saey

Tina Hesman Saey is the senior staff writer and reports on molecular biology. She has a Ph.D. in molecular genetics from Washington University in St. Louis and a master’s degree in science journalism from Boston University.

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