Obesity surgery breakthrough with fat-busting bacteria find

The most radical form of weight loss – gastric bypass or bariatric surgery – may have longer term effects that go way beyond reducing the amount of calories the body can absorb.

A new study involving laboratory mice, by researchers at Massachusetts General Hospital and Harvard University, suggests the surgery does not just re-route the digestive tract but also alters bacteria in the gut.

In technical terms, fecal samples obtained before and after Roux-en-Y gastric bypass surgery showed a rapid and sustained increase in Gammaproteobacteria (primarily Escherichia) and Verrucomicrobia (Akkermansia). The change occurred independent of weight loss and caloric restriction, and was evident across the entire gastrointestinal tract.

In non-scientific terms, the surgery somehow replaces fattening microbes with slimming ones.

If that occurs in people, too, then the same bacteria change achieved by gastric bypass might be accomplished without putting obese patients through an expensive and risky operation.

For many patients, particularly those with type 2 diabetes, gastric bypass has succeeded where nothing else has. Severely obese patients routinely lose 65% to 75% of their excess weight and fat after the operation and leave their diabetes behind.

Oddly, however, the diabetes remission often occurs before significant weight loss. That has made bypass surgeons and weight-loss experts suspect that Roux-en-Y changes not only anatomy but also metabolism or the endocrine system.

The new study was aimed at finding out whether the microbial change was the cause or the effect of post-bypass weight loss.

The researchers first performed Roux-en-Y on obese mice. As expected, the animals quickly slimmed down, losing 29% of their weight and keeping it off, the researchers report in the journal Science Translational Medicine.

The scientists performed “sham” Roux-en-Y on other obese mice but instead transferred gut microbiota from the Roux-en-Y mice to microbe-free obese mice. The recipient mice lost weight and fat. Crucially, obese mice that received gut bugs from mice that had received sham Roux-en-Y, not the real thing, did not slim down.

“The effects of gastric bypass are not just anatomical, as we thought,” says Dr Lee Kaplan, senior author of the study and associate professor of medicine at Harvard Medical School. “They’re also physiological. Now we need to learn more about how the microbiota exert their effects.”

Slimming bacteria work their magic in either of two ways, studies of gut microbiota show. They seem to raise metabolism, allowing people to burn off a 630-calorie chocolate chip muffin more easily.

They also extract fewer calories from the muffin in the first place. In contrast, fattening bacteria wrest every last calorie from food.

Transferring slimming bacteria into obese people might be one way to give them the benefits of weight-loss surgery without an operation. It might also be possible to devise a menu that encourages the proliferation of slimming bacteria and reduces the population of fattening bacteria.