Move over, dieting! Taming your gut bugs may help you shed flab, according to a new Harvard study.

Altering the composition of the bacterial colony living in the gut may provide a tool to weight-loss, found the study conducted in collaboration with researchers at Harvard-affiliated Massachusetts General Hospital.

The study, published in Science Translational Medicine, hints at a future where doctors could deliver the weight-loss benefits of gastric bypass surgery without the surgery.

“Simply by colonising mice with the altered microbial community, the mice were able to maintain a lower body fat, and lose weight to about 20 per cent as much as they would if they underwent surgery,” said Peter Turnbaugh, senior author of the study.

“Our study suggests that the specific effects of gastric bypass on the microbiota contribute to its ability to cause weight loss, and that finding ways to manipulate microbial populations to mimic those effects could become a valuable new tool to address obesity,” said other senior author, Lee Kaplan 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,” said Kaplan.

While there had been hints that the microbes in the gut might change after bypass surgery, the speed and extent of the change came as a surprise.

In earlier experiments, researchers had shown that the guts of both lean and obese mice were populated by varying amounts of two types of bacteria - firmicutes and bacteroidetes. When mice undergo gastric bypass surgery, however, it “resets the whole picture,” Turnbaugh said.

“The post-bypass community was dominated by proteobacteria and verrucomicrobia, and had relatively low levels of firmicutes,” he said.