NEW YORK (Reuters Health) - Obesity surgery can cause type 2 diabetes to go into remission, but much depends on how much weight the patient loses within the first few months, a new study suggests.

Gastric bypass surgery for severe obesity has been shown to control type 2 diabetes, a disorder that commonly goes hand-in-hand with obesity. The procedure involves sectioning off a small portion of the stomach, creating a pouch that limits the amount of food a person can eat in one sitting.

The surgeon also adds a bypass that re-routes food past the rest of the stomach and part of the small intestine to limit calorie and nutrient absorption.

It's thought that the surgery creates hormonal changes that, in turn, improve diabetes control.

However, the new study, by surgeons at Duke University Medical Center in Durham, North Carolina, shows that hormones are not the whole story. The amount of weight patients shed in the first six months after surgery appears key to diabetes remission.

"Gastric bypass surgery appears to cause important metabolic effects that rapidly improve type 2 diabetes, but weight loss itself is also extremely important," Dr. Eric DeMaria said in an interview with Reuters Health.

DeMaria presented his group's research this week at the annual meeting of the American Society for Metabolic and Bariatric Surgery in Washington, DC.

He and his team followed 71 morbidly obese patients with severe diabetes requiring high doses of insulin and oral medications to control their blood sugar levels. The researchers' goal was to identify factors that differentiate patients who go into remission from those who do not.

"We found that the most important factor was the amount of weight loss by the patient," DeMaria said.

Diabetes control was improved in all patients as evidenced by better long-term blood sugar levels and reductions in the amount of medication they needed. Still, only 48 percent went into complete remission.

The researchers found that weight loss in the first three weeks to six months after surgery was a critical factor in diabetes remission.

The hormonal effects of gastric bypass surgery are still important.

"Morbidly obese patients usually lose about 10 percent of their body weight within three weeks of surgery," DeMaria said, "but that does not explain why they can cut back on their medications within the first day or two."

That benefit, he explained, "appears to be an effect on gut hormones, with dramatic improvement in insulin resistance."

"But," DeMaria added, "it is interesting to recognise that faster weight loss and greater amount lost improves the chance that patients will remain in remission."

The findings, he said, suggest that "if we can enhance the weight-loss effect of surgery — by adding medications or rigorous behaviour modification — we may do better than a 50 percent remission rate."