Weight loss surgery appears to change the body’s metabolism in a way that dieting alone cannot, helping to explain why diabetes often disappears after the surgery even before much weight is lost, U.S. researchers said on Wednesday.

Understanding how gastric bypass affects metabolism could shed light on treatments for type 2 diabetes, a global epidemic strongly linked with obesity and too little exercise.

Weight loss surgery is becoming increasingly popular as obese people struggle to lose weight and avoid the health complications that accompany the extra pounds - including diabetes, heart disease, joint pain and some cancers.

In research conducted at Columbia University in New York and Duke University in North Carolina, researchers studied two small groups of severely obese diabetic patients who either had gastric bypass surgery or went on strict diets.

Both groups lost about 20 pounds.

For the study, the teams measured metabolites - chemical byproducts of foods in the body.

They found that unlike dieting, gastric bypass changes a person’s metabolism by significantly reducing levels of circulating amino acids - compounds linked with obesity, diabetes and insulin resistance.

“What we were trying to do is cast a very wide net,” said Christopher Newgard of Duke, who worked on the study published in Science Translational Medicine.

“What we caught is a very clear difference between bariatric surgery and dietary intervention.”

He said patients in the surgery group had lower levels of molecules known as branch chain amino acids.

“These dropped much more precipitously in people having bariatric surgery than people having the dietary intervention,” he said.

People in the gastric bypass arm of the study underwent a surgery known as Roux-en-Y, in which doctors surgically reduce the size of the stomach to prevent people from eating too.

Newgard said it is not clear why reducing stomach size might have this effect, but it is clear that bariatric surgery results in significant metabolic changes.

The team is now looking to discover ways to develop drugs that could replicate this effect.

Newgard said the results might not apply to Allergan’s Lap-Band weight-loss device, in which doctors insert an adjustable silicone band around the upper part of the stomach but do not surgically reduce the size of the stomach.

Up to a third of U.S. adults could suffer from diabetes by 2050, according to the U.S. Centers for Disease Control and Prevention.

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By Julie Steenhuysen

CHICAGO