Gastric bypass surgery, in which the stomach is stitched into a tiny pouch, has long been seen as a last resort for the dangerously obese. Doctors attributed rapid post-surgical weight loss to reduced hunger and restricted eating resulting from the smaller stomach.
But new evidence suggests weight loss may result when the procedure alters the types of microbes in the gut.
Scientists reached this conclusion by transferring microbes from bypass-treated obese mice to a group of lean mice raised in sterile conditions that left them with no intestinal bacteria at all. Two weeks after the transfer, recipient mice had lost considerable weight; another group that received microbes from obese mice in a placebo group — undergoing surgery without gastric bypass — stayed the same.
The new microbiota may trigger weight loss, says gastroenterologist Lee Kaplan of Massachusetts General Hospital, by sending chemical signals that cause the human host to burn more calories, which helps use up the body’s fat reserves.
“The physiology of the whole body changes in response to bypass surgery — it’s not just a matter of making the stomach smaller so people eat less,” says Kaplan. “If we can uncover which changes are responsible for what the surgery does, we can devise less invasive treatments,” including drugs or microbial transplants that would set the microbiome right.