Weight-loss surgery can dramatically improve the ability to control diabetes in mildly to moderately obese patients, according to a major study by University of Minnesota researchers.

The study, one of the largest of its kind, found that diabetics who had gastric-bypass surgery not only lost weight but also doubled their chances of achieving healthy levels of cholesterol, blood sugar and blood pressure a year later.

But the study also served as a reminder that the surgery can be risky.

More than a third of the patients reported "serious adverse events," including one patient who suffered brain damage from complications of the operation.

As a result, the potential benefits "must be weighed against the risk of serious adverse events," the authors wrote in Wednesday's Journal of the American Medical Association.

This is not the first study to show that weight-loss surgery can help control diabetes, which is linked to obesity. But it's one of the most ambitious, said Dr. Sayeed Ikramuddin, a University of Minnesota surgery professor who led the study. It included 120 diabetes patients in Minnesota, New York and Taiwan, and focused on one of the most popular types of weight-loss surgery, known as Roux-en-Y gastric bypass.

As part of the study, all volunteers received an intensive program of diet, exercise and medication — but only half had the surgery.

The surgery patients lost, on average, 26 percent of their body weight in a year, compared to 8 percent in the control group.

In addition, 49 percent of the surgery patients were able to lower their cholesterol, blood sugar and blood pressure rates to the target levels set by the American Diabetes Association. By comparison, only 19 percent of the control group reached those goals.

'Nowhere to go'

LaVonne A. Swenson of Morton, Minn., had the surgery almost two years ago as part of the study. Since then, she says she's lost 85 pounds and no longer needs medication for her blood pressure or diabetes.

"I'm a new person," said Swenson, 64. As a Native American, she said she was worried about the high rate of diabetes in her community, and credits the program for inspiring her to change her diet and become more active. "It has changed my lifestyle," she said.

The overall results were "really powerful," said Ikramuddin, noting that this is the first study to "really look at surgery compared to the best medical management." It confirms that it's difficult for people to make enough progress by lifestyle changes alone.

But an editorial in the same journal raised concerns about the higher complication rate in the surgical group, calling it "problematic."

The scientists reported 22 "serious adverse events" among the 60 patients in the surgery group, compared to 15 in the same-size control group. Though not all could be blamed on the surgery itself, the complications included leaks, infections, bleeding ulcers and bowel obstructions.

But Ikramuddin said patients should weigh the risks of the surgery against those of uncontrolled diabetes: heart attacks, strokes, amputations. "These patients have nowhere to go," he said. "If you interpret it in that light, that changes the dynamic a great deal. You're looking at people, they're going off a cliff."

Maura Lerner • 612-673-7384