Obese people who have weight-loss surgery gain at least six years of health benefits that include fewer diabetes cases and lower cholesterol and blood pressure. Even so, their medical costs do not drop.

While the advantages linked to diminished fat were found to be durable over six years in a study published Tuesday, a second report tied the surgery to complications such as gallstones and anemia that increased medical expenses for patients over the same period.

The research was included in an obesity-themed issue of the Journal of the American Medical Association.

Drug therapy and lifestyle changes have been largely ineffective in curtailing obesity, so the weight-loss surgery investigators examined the results of the procedure in 1,156 volunteers. The patients who underwent gastric bypass surgery lost an average of 28 percent of their body weight, while those who didn't get surgery stayed the same or even gained a few pounds, the study found.

Almost two-thirds of the surgery patients saw their blood sugar level return to normal, with hypertension, cholesterol and triglycerides down.

Researchers were surprised by the results of the separate study that weighed cost benefits from the surgery, said Martin Neovius from the Karolinska Institute in Sweden, the lead author. The study tracked 2,010 adults who underwent weight-loss surgery between 1987 and 2001, and compared their results to similar people not having surgery.

The researchers found that surgery patients spent 54 days in the hospital in the two decades after their operations, compared with 40 days for the comparison group. Drug costs for the surgery patients, however, did drop significantly.

BLOOMBERG NEWS