Gastric Bypass May Cause Changes In Gut Microbes Leading To Weight Loss
March 28, 2013

Microbial Changes Following Gastric Bypass May Play A Role In Weight Loss

redOrbit Staff & Wire Reports - Your Universe Online

Changes that occur in the microbial organisms of a person´s gastrointestinal tract may be responsible for some of the weight-loss benefits that follow gastric bypass surgery, and transferring those microscopic organisms into another individual could have similar effects, according to a new study.

Researchers at Harvard University and Massachusetts General Hospital (MGH) studied three groups of mice. At the start of the study, each group was obese as a result of a high-fat, high-carbohydrate diet. One group was given a common version of gastric bypass surgery known as the Roux-en-Y procedure, while the other two were given false operations in which a portion of their gastrointestinal tract was separated and later reattached.

One of the false surgery groups had no changes to their diet, while the other was place on a reduced-calorie eating plan in order to encourage weight loss, the researchers explained. A week after the procedure, there were significant changes to the gastrointestinal microbes in the mice that had received the bypass — specifically, an increase in bacteria typically discovered in leaner individuals and a decrease in those organisms linked to obesity.

Twenty-one days following the surgery, the bypass rodents had lost nearly one-third of their body weight. Meanwhile, minimal change was discovered in the gastrointestinal microbes that received the fake procedures, though no additional weight loss was observed in the restricted diet group when compared to the high-fat, high-calorie group — both had lost approximately the same amount of weight. The researchers observed that the bypass mice were expending more energy than the other groups, even though there were no changes in activity levels.

“To determine more precisely the effects of bypass-associated microbial changes, the investigators transferred samples of the gastrointestinal contents from each of the three groups into lean mice with germ-free gastrointestinal systems,” MGH officials explained in an official statement. “Two weeks later, the animals receiving samples from bypass mice had lost a significant amount of weight, while those receiving samples from the sham-treated mice — including those that had lost weight through dietary restriction — had no change in weight.”

Additional research will be required to determine exactly how the changes in those gastrointestinal microbes lead to weight loss, but the researchers did observe changes in the proportion of a specific group of nutrients known as short-chain fatty acids. The changes to those fatty acids lead the Harvard and MGH team to believe that the way that various groups of microbes process different types of foods could lead to a significant change in the overall metabolism of a creature, especially since those fatty acids are known to play a role in metabolic regulation.

"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 Lee Kaplan, director of the Obesity, Metabolism and Nutrition Institute at MGH and the other senior author of the paper.

“We need to learn a good deal more about the mechanisms by which a microbial population changed by gastric bypass exert its effects, and then we need to learn if we can produce these effects — either the microbial changes or the associated metabolic changes — without surgery,” he added. “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.”

Their findings have been published in the March 27 edition of the journal Science Translational Medicine.