Bacteria that live in the gut change after gastric-bypass surgery, and may aid in weight loss, according to a Harvard University study.
Researchers gave mice the stomach-shrinking surgery and monitored changes in the gut's bacterial inhabitants, according to a study in the journal Science Translational Medicine. When bacteria from the mice that got surgery were transferred into mice with no gut germs, those mice also lost weight, about a fifth of what they would have lost with surgery.
Gastric surgery helps people lose weight by shrinking the size of the stomach, making it tougher to absorb calories. Now scientists think it may also adjust gastrointestinal bacteria, contributing to weight loss and raising the possibility for less-drastic obesity treatments, according to the authors.
"A major gap in our knowledge is the underlying mechanism linking microbes to weight loss," said Peter Turnbaugh, a study author and systems biologist at Harvard, in a statement released by the university. "There were certain microbes that we found at higher abundance after surgery, so we think those are good targets for beginning to understand what's taking place."
The researchers fed three groups of mice a high-fat, high- carbohydrate diet that made them obese. One group received the most-common version of gastric bypass, called Roux-en-Y. Two other groups received "sham" operations, where the animals' intestines were cut and sewn back together. One group of those who received the sham operation continued eating the same diet as before; another group was put on a weight loss diet.
After a week, the mice who received weight-loss surgery had changes in the numbers and kind of microbes that lived in their gut, the study found. Three weeks later, the mice had lost a third of their body weight. By comparison, there was little change in the bacteria of mice that underwent the sham slicing, even though those in the controlled diet group also lost the same amount of weight.
The scientists then transferred the microbes from the surgically-altered mice into mice whose stomachs lacked their own bacteria. Those mice also lost weight while other sterile mice receiving bacteria from either group didn't.
It's not clear what about the bacteria caused weight loss, the study authors said.
"We need to learn a good deal more about the mechanism by which a microbial population changed by gastric bypass exerts its effects," said Lee Kaplan, a study author and director of the Obesity, Metabolism, and Nutrition Institute at Massachusetts General Hospital, in a statement. " 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."