Diabetics who undergo gastric bypass surgery could be at disadvantage compared to other patients, a new study suggests.

Researchers at the University of California, San Francisco, examined data of 310 patients with an average body mass index (BMI) of 52 who underwent gastric bypass surgery. Of the participants, 114 had diabetes. The researchers evaluated the patients a year after the surgery and 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 who have diabetes and take insulin or other drugs that stimulate the production of fat and cholesterol are 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, director of the Bariatric Surgery Program at University of California, and colleagues wrote.

Another problem is represented by the stomach pouch size, which is an important part of the procedure. Many bariatric surgeons use a standard technique for creating the gastric pouch, but they have to take into consideration the characteristics of each individual patient.

In previous studies, bypass surgery was found to reduce the risk of heart disease, diabetes and cancer in obese people.

The study was published in the September issue of the journal Archives of Surgery.

Gastric bypass surgery (Roux-en-Y gastric bypass), which is the favored bariatric surgery in the United States, changes the anatomy of a patient’s digestive system in order to restrict food intake. The surgeon creates a smaller stomach pouch that bypasses large sections of the digestive system. According to the American Society for Metabolic & Bariatric Surgery (ASMBS), about 205,000 people had some form of bariatric surgery last year.