Bacteria may give surgery extra boost

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LOS ANGELES — In the latest of a slew of studies examining the role of the so-called microbiome — the mix of microscopic critters that colonize our bodies and our environment — in human health, Harvard researchers said Wednesday that part of the reason that Roux-en-Y gastric bypass surgery works so well in helping people lose weight is because it causes changes in the mix of bacteria in our bellies.

The discovery suggests that doctors might someday be able to mimic the microbial effects of weight-loss surgery without putting patients under the knife, said Dr. Lee Kaplan, director of the Obesity, Metabolism and Nutrition Institute at Massachusetts General Hospital and co-senior author of a report detailing the research in the journal Science Translational Medicine.

"The ability to achieve even some of these effects without surgery would give us an entirely new way to treat the critical problem of obesity," he said, in a statement.

It had been known that people and rats who have Roux-en-Y surgery, which reduces the stomach's capacity and bypasses some of the intestine, experience changes in the bacterial populations that inhabit their digestive systems.

But researchers were uncertain whether the surgery it self caused the shifts, or if the changes resulted from subsequent weight loss.

To try to answer that question, Kaplan and fellow senior author and Harvard biologist Peter Turnbaugh conducted an experiment on mice. In the first part of the experiment they performed gastric bypass surgery on obese mice; observed their subsequent weight loss, metabolic performance and gut microbes; and then compared their findings with the same measures in obese mice who had sham surgeries and remained overweight or who had sham surgeries and then lost weight on a diet of lower-calorie chow.

They found that the Roux-en-Y mice lost about 30 percent of their body weight within three weeks, while the sham-surgery mice who didn't go on the weight-loss diet regained their body weight in the same amount of time. Examining fecal samples and tissues from all three groups of animals, they found that the Roux-en-Y mice had changes in their gut microbes that weren't shared by the other two groups, including the lean mice who lost weight by dieting.

The results suggested that the surgery itself — rather than the weight of the animals — was what altered the gut microbiota.