Bariatric Surgery and Prevention of Type 2 Diabetes

Previous studies have demonstrated associations between obesity and type 2 diabetes, and between changes in body weight and incident type 2 diabetes. There is also an association between the increase worldwide in obesity and the increased prevalence of type 2 diabetes. There are 285 million people with diabetes at present; it is estimated that the number will increase to 439 million by 2030.

Among persons with prediabetes, effective lifestyle changes and drug treatment can reduce the incidence of type 2 diabetes by 40% to 45%; the effects have been shown to last from 3 to 15 years after the interventions. Studies to date have focused on persons with moderate obesity, however, the highest risk of type 2 diabetes occurs in people with severe obesity. Among persons with severe obesity, bariatric surgery is the only treatment that has been shown to have long-lasting effects resulting in large, sustained weight loss.

According to researchers, there have been few studies assessing the effect of surgery on the prevention of type 2 diabetes. The SOS (Swedish Obese Subjects) study was a nonrandomized, prospective, controlled intervention trial that compared the long-term effects of bariatric surgery with usual care. The current study was an analysis of data from SOS to determine whether surgery could prevent type 2 diabetes. Results of the analysis were reported in the New England Journal of Medicine [2012;367(8):695-704].

The analysis included data on 1658 obese patients who underwent bariatric surgery (surgery group) and 1771 obese matched controls (control group). Matching was performed on a group, not individual, level. All patients in both groups entered the study with the intention to lose weight. None of the participants had diabetes at baseline.

Patients in the surgery group underwent banding (n=311), vertical banded gastroplasty (n=1140), or a gastric bypass procedure (n=207). Patients in the control group received usual care for obesity. Usual care in Sweden ranged from advanced lifestyle interventions (eating behavior, food selection, energy intake, and physical activity) to no treatment.

The rate of incident type 2 diabetes was a specified secondary end point of the original study. At the time of this analysis, the participants had been followed for up to 15 years. There were some differences between the groups included in the analysis: baseline body weight was higher and risk factors were more pronounced in the surgery group compared with the control group.

At the 15-year follow-up point, 36.2% of the original participants had dropped out of the study and 30.9% had not yet reached the time for their 15-year follow-up examination, resulting in an unadjusted 15-year participation rate of only 32.9%. Following adjustment for follow-up of <15 years and for death, the 15-year participation rate was 53.5%.

During the follow-up period, 329 participants in the control group developed type 2 diabetes compared with 110 in the surgery group; incidence rates were 28.4 cases per 1000 person-years in the control group and 6.8 cases per 1000 person-years in the surgery group (adjusted hazard ratio with surgery, 0.17; 95% confidence interval, 0.13-0.21; P<.001).

The absence or presence of impaired fasting glucose influenced the effect of bariatric surgery (P=.002 for the interaction); however, body mass index did not (P=.54). The overall conclusions were not altered with sensitivity analyses, including end-point imputations. Postoperative mortality was 0.2%, and 32.8% of patients undergoing bariatric surgery experienced complications requiring reoperation within 90 days of the original surgery.

In conclusion, the researchers said, “Bariatric surgery appears to be markedly more efficient than usual care in the prevention of type 2 diabetes in obese persons. Our data indicate that bariatric surgery has a preventive effect on incident type 2 diabetes, particularly in participants with impaired fasting glucose.”