Contrary to other studies, a new study found that people with diabetes did not lose as much weight as other patients after the surgery. Gastric bypass is an operation used to treat morbid obesity (the severe accumulation of excess weight as fatty tissue) and the health problems it causes. The surgery involves sectioning off a small portion of the stomach in order to create a pouch which limits the amount of food a person can eat in one sitting. The surgeons restrict food intake by creating a smaller stomach pouch that bypasses large sections of the digestive system.

Led by Dr. Guilherme Campos, director of the Bariatric Surgery Program at University of California, San Francisco, the study involved 310 patients who were evaluated a year after Roux-en-Y bypass surgery. Before gastric bypass surgery, the 310 patients had an average body mass index (BMI) of 52. At baseline, 114 patients had diabetes. After the surgery, the researchers found that 38 of the patients had poor weight loss, defined as a loss of 40% or less of excess weight at baseline.

At the end of the study, researchers found that gastric-bypass patients with diabetes did not lose as much weight as other patients after the surgery. 92% of participants without diabetes were able to lose more than 40% of their excess weight, while only 79% of patients with diabetes were able to lose that much weight after a year.

People with diabetes take insulin or other drugs that stimulate the production of fat and cholesterol, the researchers added. Those who had pre-operative insulin therapy were less likely than others to have good weight loss after the procedure.

“The weight gain associated with the use of insulin and insulin secretagogues may create a vicious cycle and a risk of worsening the patient’s insulin resistance and other conditions,” Dr. Campos and colleagues wrote.

The researchers added that proper stomach pouch size is an important part of the procedure, but most bariatric surgeons use a standard method for creating the gastric pouch. Surgeons have to take into consideration the characteristics of each individual patient, which are different. “As the use of gastric bypass continues to grow, we believe it is critical to stress the importance of, and to teach the creation of, the small gastric pouch and to better understand the technique used for pouch creation,” the study authors wrote.

The researchers also noted that post-bypass diabetes therapy should focus on metformin and incretin-type drugs that are less likely to promote weight gain. Campos said the solution may be to rely on newer anti-diabetes drugs, such as the DPP-IV inhibitors, like Januvia, that can help patients keep their blood sugar and weight under control.

However, researchers think the maximum benefits may be achieved by those obese patients who are recently diagnosed with diabetes because they are more likely to regain their normal sugar metabolism after bypass surgery.

The study conducted by Dr. Campos and colleagues was published in the September issue of the journal Archives of Surgery.

About 15 million Americans are morbidly obese, with a body mass index of 40 or more. According to the American Society for Metabolic & Bariatric Surgery (ASMBS), about 205,000 people had some form of bariatric surgery last year. The most common forms of weight-loss surgery are gastric bypass and gastric banding.