Researchers report that a new operation known as the duodenal switch produces more weight loss in the super-obese than gastric bypass, the standard operation.

Three years after surgery, 84% of super-obese people who had the duodenal switch operation had lost more than half of their excess weight, compared to 60% of those treated with the Roux-en-Y gastric bypass.

Super-obese is defined as a body mass index (BMI) of at least 50. This typically means carrying at least 150 pounds more than ideal weight.

"While there is no single ideal procedure that can be applied to all severely obese patients, we have generally recommended the duodenal switch for those with a BMI greater than 50," said study author Vivek Prachand, M.D., of the University of Chicago. "This study confirms that approach. Both procedures appear to be reasonably safe in the hands of an experienced team, but the duodenal switch appears to offer a considerable advantage in terms of the amount and possibly the duration of weight loss."

The study results appear in the October 2006 issue of the Annals of Surgery.

The super-obese make up only a fraction of all overweight people, but their numbers are increasing faster than any other subgroup. When the term was coined in 1987, fewer than one in 2,000 adults in the United States met the criteria of a BMI greater than 50. (A normal BMI is 18.5 to 24.9. From 25 to 29.9 is considered overweight.Thirty or above is considered obese). The number of super-obese Americans has quintupled since then, to one in 400 U.S. adults in 2000.

At the same time, bariatric or weight-loss surgery has become very common, increasing from 16,000 cases in 1992, to 63,000 in 2002, to 171,000 in 2005. By far the most common of these operations is the gastric bypass, which involves stapling off a large portion of the stomach to make overeating difficult, and rerouting the intestines to reduce the absorption of calories. The less common duodenal switch leaves a slightly larger stomach pouch but makes even more drastic alterations to the intestines to limit absorption, particularly of fats and starches.