Gut bacteria may be key to weight loss

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D. Anderson lab/Caltech

Normally we shudder when we think of bacteria, but a new study reveals that some of these microorganisms may be able to help us lose weight.

The study, published in the March 27 issue of Science Translational Medicine, showed that bacteria in the guts of mice changed after they had gastric bypass surgery, a procedure in which surgeons divide a person's stomach and connect the small intestine directly to the smaller walnut-sized portion. When these different microbes were transplanted in sterile mice who did not have the surgery, those animals lost weight quickly.

"Simply by colonizing mice with the altered microbial community, the mice were able to maintain a lower body fat, and lose weight - about 20 percent as much as they would if they underwent surgery," senior author Peter Turnbaugh, a Bauer Fellow at Harvard's Faculty of Arts and Sciences (FAS) Center for Systems Biology, said in a press release.

For the experiment, the researchers performed the gastric bypass surgery on a group of obese mice and recorded their weight loss, metabolic performance and gut microbe levels. They then compared their progress to other obese mice who had placebo surgeries and stayed overweight or had placebo surgeries and then were placed on a lower-calorie food diet.

The mice who had the gastric bypass surgery lost about 30 percent of their body weight in three weeks and had different bacteria in their stools than the other two groups. The mice who had the placebo surgery and didn't go on a weight loss diet regained the weight they initially lost by the end of three weeks. That suggests the surgery, not the weight loss, changed the microbes in the mice.

To further confirm the results, lean, germ-free mice received gut microbes from one of the three groups. Those that got the bacteria from the gastric bypass mice lost weight and fat, while the others did not.

Turnbaugh said that though the numbers seem high, weight loss could have been even greater. Because the mice who received the bacteria weren't on a special diet to increase their weight, there could be an even more drastic weight loss if the mice were eating high-fat or high-calorie food, he said.

The study shows that gastric bypass may be successful for weight loss for more reasons than just simply making the stomach smaller and shortening the area where the body absorbs calories. But, scientists don't exactly know why or how the bacteria changes just yet.

"We know the effects of bariatric surgery are not just mechanical and we don't know the full reasons why it works so well, especially in the resolution of diabetes," Dr. David Haslam, associate professor of pediatrics and molecular microbiology at Washington University in St. Lewis, told the BBC. "There is more to it than meets the eye."

It's still a long way before this process is replicated in humans, but the researchers hope that one day they will be able to use this method to help dangerously obese people lose weight without surgery. One of the problems with the study is that the bacteria was able to be transplanted in germ-free mice, but it will be hard to do that for humans, Jeffrey Cirillo, a professor with the department of microbial and molecular pathogenesis at Texas A & M Health Science Center, explained to HealthDay.

However, for people who just need to lose a few pounds here or there, Turnbaugh still thinks hitting the gym is their best option.

"It may not be that we will have a magic pill that will work for everyone who's slightly overweight," he said. "But if we can, at a minimum, provide some alternative to gastric bypass surgery that produces similar effects, it would be a major advance."

"We need to learn a good deal more about the mechanisms by which a microbial population changed by gastric bypass exert its effects, and then we need to learn if we can produce these effects - either the microbial changes or the associated metabolic changes -- without surgery," senior author Lee Kaplan, an associate professor of Medicine at Harvard Medical School, added in a press release. "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, one that could help patients unable or unwilling to have surgery."