How Weight Loss Surgery Helps Diabetes

Study Explains Why Surgery Improves Blood Sugar Levels Even Before Patients Lose Weight

By Salynn Boyles
WebMD Health News

Reviewed By Louise Chang, MD

Sept. 2, 2008 — Obese diabetes patients who have gastric bypass weight loss surgery often show dramatic improvement in blood sugar control within days, long before significant weight loss occurs.

The reversal of type 2 diabetes tends to occur much more rapidly than with gastric banding, and a new study may help explain why.

The findings could also advance the search for better diabetes treatments that target the small intestine and not the pancreas, researchers say.

"It is increasingly clear that the intestine is not just a conduit for food transit," gastric bypass surgeon Francesco Rubino, MD, tells WebMD. "We now know that it is also a very important organ for the regulation of glucose."

Intestine Produces Glucose

Several recent studies have suggested that weight loss surgery is a more effective treatment for type 2 diabetes in obese people than standard treatments for the disease.

Because weight loss alone cannot explain the rapid remission of disease in many gastric bypass patients, researchers have looked for other causes.

One theory has been that surgery alters the expression of hormones that help control appetite, blood sugar, and weight.

But studies designed to test this hypothesis have proven contradictory, diabetes researcher Gilles Mithieux tells WebMD.

In their newly published study, reported in the September issue of the journal Cell Metabolism, Mithieux and colleagues looked elsewhere for answers.

"We know from earlier work that the small intestine can produce glucose," he says. "We showed that with gastric bypass surgery you essentially double the capacity of the intestine to do this."

By studying mice treated with either gastric bypass or banding, researchers confirmed that the bypass operation was associated with increased production of glucose, or blood sugar, in the small intestine, while gastric banding was not.

Gastric bypass surgery essentially produces a "double intestine," Mithieux says. The portion of the small intestine that is closest to the stomach is bypassed so that it no longer received nutrients. The lower small intestine is then attached to the stomach where it becomes the main nutrient receiver.

By surgically repositioning the lower small intestine, which usually does not produce much glucose, it ramps up intestinal glucose production and improves insulin sensitivity, he says.

Treating Diabetes With Surgery

Rubino tells WebMD that the findings offer important insights into the role of the small intestine in blood sugar regulation.

"This doesn't tell the whole story, but it appears to be an important piece of the puzzle," he says.

The gastric bypass surgeon is a strong advocate of using the surgery as a first-line treatment for type 2 diabetes — a position that remains controversial.

He directs the diabetes surgery center at the New York-Presbyterian Hospital/Weill Cornell Medical Center.

"Surgery promises to be one of the most powerful resources we have to fight this disease," he says. "I don't think it will be the answer for everyone. But for patients with the right profile, the results can be remarkable."

Rubino believes that the surgery can help not just diabetic patients who are morbidly obese, but also people who are overweight but don't weigh enough under current guidelines to be considered for the gastric bypass procedure.

"We hope to study this to see if surgery is better than conventional treatment in patients who are moderately obese or just overweight," he says.

SOURCES: Troy, S. Cell Metabolism, September 2008; vol 8: pp 201-211. Gilles Mithieux, Institut National de la Sante et de la Recherche Medicale, Paris. Francesco Rubino, MD, director, metabolic surgery program, New York-Presbyterian/Weill Cornell Medical Center, New York City.

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