WEDNESDAY, June 18 (HealthDay News) -- Weight loss plays a major role in improving diabetes after obese patients have stomach-reduction surgery, say Duke University Medical Center researchers.

Previous studies have suggested that gastric bypass surgery -- which re-routes how food is sent from the stomach to the small intestine -- helps improve diabetes by causing changes in the way hormones are secreted from the gut and pancreas.

But the metabolic effects shouldn't overshadow the importance of losing weight after surgery, the Duke team said.

"Yes, there are physiologic changes related to the restructuring of the gastrointestinal or GI tract that appear to influence the rapid improvement in diabetes following gastric bypass. But our study shows the patients who were able to get off medications completely and go into remission were the ones who lost the most weight," Dr. Eric DeMaria, director of bariatric surgery at Duke University Medical Center, said in prepared statement.

The more weight patients lost, the higher the likelihood of diabetes improvement, DeMaria and colleagues found.

They studied 314 obese diabetic patients who had gastric bypass surgery. Of those patients, 71 had severe diabetes that required insulin therapy because oral medications weren't sufficient to control the disease.

Overall, gastric bypass surgery had a beneficial effect on diabetes. After 12 months, all the patients were able to reduce the dose or number of their diabetes-related medications. Of the 71 patients with severe diabetes, 48 percent achieved remission of their disease.

Losing weight during the first three weeks to six months after gastric bypass surgery was critical for patients who achieved diabetes remission, DeMaria said.

To achieve long-lasting diabetes improvement following weight-loss surgery, "we need to tell patients to pay attention to their weight and to do things that enhance weight loss. That can only be accomplished by changing patient behavior and lifestyle," he said.

The study was expected to be presented Wednesday at a meeting of the American Society for Metabolic and Bariatric Surgery.

More information

The U.S. Centers for Disease Control and Prevention has more about diabetes.