WEDNESDAY, June 20 (HealthDay News) -- Black women without diabetes lost about 10 percent less weight than white women after having a weight-loss procedure called gastric bypass surgery, but having diabetes helped increase their weight loss, a new study finds.

For the study, Duke University researchers compared outcomes among nearly 300 obese white and black women with an average age of 40 who underwent gastric bypass surgery, a procedure that makes the stomach smaller in order to help people lose weight.

Overall, black women lost nearly 57 percent of their excess weight in the three years after surgery; white women lost less than 65 percent. Black women with type 2 diabetes, however, lost about 60 percent of their excess weight, the investigators found.

Among women with diabetes, both blacks and whites had similar diabetes remission rates (75 percent and 77 percent, respectively) after the surgery, according to the study, which is scheduled for presentation Wednesday at the annual meeting of the American Society for Metabolic & Bariatric Surgery in San Diego.

"For some reason, diabetes was the great equalizer when it came to weight loss," study co-author Dr. Alfonso Torquati said in a society news release. "[Black] women with type 2 diabetes lost a similar amount of excess weight as [white] women. Racial differences in excess weight loss only emerged between non-diabetic women."

"Further study is needed to determine if the reasons are genetic or because of differences in body-fat distribution or both," said Torquati, director of the Duke Center for Metabolic and Weight Loss Surgery.

Although the study uncovered an association between having diabetes and greater weight loss after the surgery in black women, it did not prove a cause-and-effect relationship.

In addition, because this study was presented at a medical meeting, the data and conclusions should be viewed as preliminary until published in a peer-reviewed journal.

More than 23 million Americans have diabetes, with type 2 diabetes accounting for more than 90 percent of cases, according to the U.S. National Institutes of Health. Nearly 13 percent of black Americans have diabetes, compared with about 7 percent of whites, according to the American Diabetes Association.

More information

The U.S. National Institute of Diabetes and Digestive and Kidney Diseases has more about weight-loss surgery.