After weight-loss surgery, new gut bacteria keep obesity away | Reuters
The logic behind weight-loss surgery seems simple: rearrange the digestive tract so the stomach can hold less food and the food bypasses part of the small intestine, allowing fewer of a meal's calories to be absorbed. Bye-bye, obesity.
A study of lab mice, published on Wednesday, begs to differ. It concludes that one of the most common and effective forms of bariatric surgery, called Roux-en-Y gastric bypass, melts away pounds not - or not only - by re-routing the digestive tract, as long thought, but by changing the bacteria in the gut.
Or, in non-scientific terms, the surgery somehow replaces fattening microbes with slimming ones.
If that occurs in people, too, then the same bacteria-changing legerdemain achieved by gastric bypass might be accomplished without putting obese patients under the knife in an expensive and risky operation.
For many obese patients, particularly those with type 2 diabetes, gastric bypass has succeeded where nothing else has. Severely obese patients routinely lose 65 to 75 percent of their excess weight and fat after the operation, studies show, 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. In other words, the surgery does something besides re-plumb the gut.
That "something," according to previous studies, includes altering the mix of trillions of microbes in the digestive tract. Not only are the "gut microbiota" different in lean people and obese people, but the mix of microbes changes after an obese patient undergoes gastric bypass and becomes more like the microbiota in lean people.
Another new study found that figuring out whether you have slimming microbiota or fattening ones might be as easy as breathing.
In a study published on Tuesday in the online edition of the Journal of Clinical Endocrinology & Metabolism, researchers at Cedars-Sinai Medical Center in Los Angeles report that people whose breath has high concentrations of both hydrogen and methane gases are more likely to have a higher body mass index and higher percentage of body fat.
Methane is associated with bacteria called Methanobrevibacter smithii, which in overabundance may cause weight gain by extracting calories from food super-efficiently, Cedars' Ruchi Mathur, who led the study, said: "It could allow a person to harvest more calories from their food."
The breath test could provide a warning that someone is at risk of obesity because he harbors fattening microbiota.
It could also validate what many overweight people have long suspected: if their slim friends eat two slices of bacon-cheeseburger pizza the 600 calories go through them like celery, but if the overweight person indulges then every calorie seems to turn into more fat. People absorb different quantities of calories from the exact same food, thanks to their gut microbiota.