Level 3: Lacking direct evidence

Results of a randomized trial reported earlier this year suggested that bariatric surgery may induce remission of type 2 diabetes in obese patients (N Engl J Med. 2012;366:1577-1585). A new analysis of data from the ongoing Swedish Obese Subjects (SOS) cohort study investigated the relation between baria­tric surgery and prevention of type 2 diabetes (N Engl J Med. 2012;367:695-704).

From a cohort of 4,047 obese patients (BMI ≥34 in men and ≥38 in women) with up to 15 years of follow-up, a group of 1,658 patients who had bariatric surgery were compared to 1,771 matched controls who did not have surgery. All patients were without diabetes at baseline.

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In the surgery group, 19% had banding, 69% had vertical banded gastroplasty, and 12% had gastric bypass. The controls received usual care, which ranged from no treatment to advanced lifestyle modification interventions. Matching was based on mean group characteristics for the entire SOS cohort using 18 demographic, anthropometric, and psychosocial variables. Significant baseline differences between the groups included higher BMI, BP, total cholesterol, and daily caloric intake in the surgery group (P<0.001 for each).

During median 10 years’ follow-up, new-onset diabetes developed in 110 patients in the surgery group and in 392 controls. The overall incidence rates per 1,000 person-years were 6.8 with surgery vs. 28.4 without surgery (P<0.001, NNT 5 for 10 years). In a subgroup of 591 patients with impaired fasting glucose at baseline, the incidence rates were 14.8 with surgery vs. 91 without surgery (P<0.001, NNT 2 for 10 years).

Alan Ehrlich, MD, is a deputy editor for DynaMed, in Ipswich, Mass., and assistant clinical professor in Family Medicine, University of Massachusetts Medical School in Worcester.

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