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Bacteria may provide some of gastric bypass surgery's boost

March 27, 2013|By Eryn Brown
  • Scientists examined shifts in the gut microbiota of obese mice after gastric bypass surgery and found that the changes among bacteria populations themselves may promote weight loss.
Scientists examined shifts in the gut microbiota of obese mice after gastric… (Associated Press )

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 itself 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% 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.

For the second phase of the experiment, the team transplanted gut microbes from the three sets of mice into lean, germ-free mice. The ones who received bacteria from the Roux-en-Y mice lost weight and fat; the mice who got transplants from the other groups did not. 

The scientists cautioned that they still didn't fully understand how changes in gut microbes cause weight loss, and that they'd need to learn more before they might apply any of what they'd learned to helping obese people lose weight.

Still, Kaplan said, the findings could provide comfort to people who have trouble controlling their weight through traditional means, because "more and more we're learning that the story is more complicated than just how much you exercise and how much you eat."

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