The study, begun in 1987, already has shown that weight loss surgery, also called bariatric surgery, can improve blood sugar levels in obese patients. The study has also shown that the surgery works much better than diet and exercise in lowering obese patients' risk of heart disease and death.
But now Lars Sjostrom, MD, PhD, of the University of Gothenburg, Sweden, and colleagues show even greater reductions in obese patients' risk of a first-time diabetes diagnosis.
"Here the risk reduction is much stronger," Sjostrom says. "In the control group, which obtained usual care, 28% of patients developed diabetes over 10 years vs. 7% of the patients in the surgery group. If you look at it 15 years later, it is 38% vs. 13% in the surgery group. These figures correspond to risk reduction of about 80% with bariatric surgery."
In people who already had rising blood-sugar levels, those who underwent weight loss surgery lowered their diabetes risk by 87%. For every 13 such people who underwent surgery, 10 would be free of diabetes after 10 years.
Weight Loss Surgery and Diabetes
The findings are "provocative and exciting," writes Duke University bariatric surgery expert Danny O. Jacobs, MD, MPH, in an editorial accompanying the report in the New England Journal of Medicine.
However, Sjostrom notes that the study is not a clinical trial. For ethical reasons, patients were not randomly given standard treatment or bariatric surgery -- which carried a 5% risk of death at the time. (Today's techniques are much safer but far from risk free.) Instead, they compared 1,658 obese people without diabetes who chose to undergo bariatric surgery to 1,771 matched obese people who did not want the surgery.
Sjostrom and Jacobs agree that further studies are needed before anyone can recommend weight loss surgery to prevent diabetes.
"There is a wealth of evidence that the operation can certainly lower the insulin requirement for patients with diabetes," Jacobs says. "But it would be a leap of faith to take it to the next level and say that a patient who is obese but not morbidly obese should undergo a surgical procedure to prevent diabetes."
Moreover, Jacobs notes, there's no information on which type of weight loss surgery would be best for preventing diabetes.
According to accepted NIH guidelines, weight loss surgery is appropriate only for people whose body mass index (BMI) is 40 or higher, or 35 or higher for those with a serious obesity-related condition such as diabetes or heart disease.
Sjostrom and colleagues found that weight loss surgery prevented diabetes regardless of a patient's BMI at the time of surgery.
To Jacobs, this suggests that the diabetes-preventing effect of bariatric surgery may be due to something other than weight loss alone.
"It is possible that interventions that are even less invasive may accomplish the very desirable goal of decreasing the incidence of type 2 diabetes and its attendant complications," he suggests.