Weight loss surgery is an increasingly popular way to treat obesity, but researchers suggest that the procedure may also lead to an unusual complication.

Researchers in this week's New England Journal of Medicine describe six cases in which people were diagnosed with noncancerous tumors in their pancreas following gastric bypass surgery. These tumors caused the pancreas to produce too much insulin, the hormone that processes blood sugar, resulting in symptoms of low blood sugar -- especially following meals.

In each case, the symptoms and low blood sugar problems resolved after surgical removal of the affected part of the pancreas.

Although it is possible that these tumors were present before the weight loss surgery, the researchers say it's their belief that the tumors formed after the surgery. They speculate that gastric bypass surgery can lead to the growth of these tumors by somehow increasing the growth factors for insulin-producing cells.

They also say that the frequency of these rare tumors in people who have gastric bypass surgery is much higher than that seen in the general population.

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Weight Loss Surgery: Is It For You?

The 'Dumping Syndrome'

Gastric bypass surgery involves making the stomach smaller and allowing food to bypass part of the small intestine. The surgery drastically limits the amount of food a person can eat and the amount of nutrients that are absorbed.

The surgery may also cause what's known as the "dumping syndrome" -- when food moves too quickly through the smaller stomach pouch and into the intestines. This can cause symptoms such as nausea, weakness, sweating, faintness, and possibly diarrhea soon after eating.

More research is needed to confirm if and how gastric bypass surgery may cause noncancerous growths in the pancreas and low blood sugar.

However, researchers say doctors should be aware of this potentially newly discovered complication of weight loss surgery and not necessarily ascribe the symptoms of low blood sugar to the dumping syndrome.

Study Weighs the Risks of Gastric Bypass

By Jennifer Warner, reviewed by Brunilda Nazario, MD

SOURCES: Service, G. New England Journal of Medicine, July 21, 2005; vol 353: pp 249-254.