New Clues to How Gastric Bypass Surgery Combats Diabetes

Gastric bypass surgery has been known to improve blood sugar control, often sending people with type 2 diabetes into remission, but experts have long wondered exactly how that happens. Now, a new study provides some clues. Circulating amino acids linked with insulin resistance decline dramatically in those who have the bypass surgery, the researchers discovered. They compared 10 obese people with diabetes who had the surgery with 11 who lost weight through dieting. "Something happens after gastric bypass that does not happen as much after the diet-induced weight loss," said Dr. Blandine Laferrere, an associate professor of medicine at St. Luke's Roosevelt Hospital Center and Columbia University, both in New York City.

The surgery, which reduces the stomach to the size of a small pouch, also modifies the junction between the stomach and small intestine. It leads to a dramatic reduction in the level of circulating amino acids that have been linked with diabetes. "The fact that gastric bypass results in the remission of diabetes in the majority of patients is not new," said Laferrere. According to background information in the study, 50 percent to 80 percent of diabetes cases go into remission after the surgery. What doctors have been trying to figure out, she said, is why the bypass surgery is so good at making the diabetes disappear. "The diabetes improves almost immediately, before a significant amount of weight loss occurs," she said. "That points out it is something other than the weight loss."

In the new study, the researchers evaluated biochemical compounds involved in metabolic reactions in the participants. Each group had lost about 20 pounds. The investigators found that the bypass patients had much lower levels of amino acids known as branched-chain amino acids, and the amino acids phenylalanine and tyrosine. "Those changes in the amino acids could be implicated in the mechanism of diabetes remission after gastric bypass," Laferrere said. Experts know the amino acids are linked with insulin resistance partly due to animal studies, she said. "If you supplement the diet of rats with branched-chain amino acids, you can induce more insulin resistance," she explained.