Bariatric Surgery Reduces the Risk of Type 2 Diabetes

Abstract & Commentary

By Jeffrey T. Jensen, MD, MPH, Leon Speroff Professor and Vice Chair for Research, Department of Obstetrics and Gynecology, Oregon Health & Science University, Portland. Dr. Jensen is a consultant for Agile Pharmaceuticals, Bayer Healthcare, HRA Pharma, and Merck; is a speaker for Bayer Healthcare and Merck; and receives research support from Agile Pharmaceuticals, Abbott Pharmaceuticals, Bayer Healthcare, HRA Pharma, and Medicines360. This article originally appeared in the November 2012 issue of OB/GYN Clinical Alert.

Synopsis: In a prospectively followed cohort of obese, non-diabetic men and women from Sweden, individuals who underwent bariatric surgery had an 83% reduction in the risk of developing type 2 diabetes over 15 years of follow-up.

Source: Carlsson LM, et al. Bariatric surgery and prevention of type 2 diabetes in Swedish obese subjects. N Engl J Med 2012;367:695-704.

Between September 1, 1987, and January 31, 2001, a total of 4047 obese persons were enrolled in the Swedish Obesity Study (SOS) intervention trial. The SOS evaluated 2010 participants who had chosen to undergo surgery (bariatric surgery group) and a non-surgical control group of 2037 subjects matched with the bariatric surgery group on the basis of 18 variables. The authors previously had reported that the matching process had unexpectedly resulted in adverse selection for the bariatric surgery group, as evidenced by a higher mean body weight and more severe risk factors than the control group. To evaluate the effect of bariatric surgery on incident type 2 diabetes, the current analysis was restricted to 1658 bariatric surgery and 1771 control subjects who did not have diabetes at baseline. Although the study groups had identical inclusion and exclusion criteria, the requirement that none of the patients have diabetes at baseline further exaggerated the adverse selection in the surgical cohort. The inclusion criteria for both the surgical and control cohorts were an age of 37-60 years and a body mass index (BMI) of ≥ 34 in men and ≥ 38 in women, and all subjects needed to have no contraindications to surgery. All subjects entered this study with the intention of losing weight; 73% of both cohorts were women. In the bariatric surgery group, 19% underwent banding, 69% vertical-banded gastroplasty, and 12% gastric bypass. Subjects in the control group received the customary treatment for obesity at their primary health care centers (e.g., lifestyle modification, including recommendations regarding eating behavior, food selection, energy intake, and physical activity). After adjustment for follow-up of < 15 years and for death, the 15-year participation rate was 53.5%. During the follow-up period, type 2 diabetes developed in 392 participants in the control group (28.4/1000 person-years) and in 110 (6.8/1000 person-years) in the bariatric surgery group (adjusted hazard ratio with bariatric surgery, 0.17; 95% confidence interval, 0.13-0.21). The effect of bariatric surgery was influenced by the presence or absence of impaired fasting glucose (P = 0.002 for the interaction) but not by BMI (P = 0.54). Sensitivity analyses, including endpoint imputations (done to adjust for the poor long-term follow-up), did not change the overall conclusions. Surgical complications included a postoperative mortality of 0.2%, and 2.8% of bariatric surgery subjects required reoperation within 90 days owing to complications. The authors concluded that bariatric surgery is markedly more efficient than usual care in the prevention of type 2 diabetes in obese persons.


As I write this, I am sitting outside noting the cooling temperatures of fall. For most of human history, the challenge in late summer was to consume as many calories as possible to store energy in the form of fat to survive the lean time of winter. Some groups evolved to be extremely efficient in converting energy to fat, and the economy of this trait varies widely in the population. Unfortunately, for modern humans eating a western diet, the challenge has changed. Winter and reduced activity arrives as it has for millennia, but now is unaccompanied by a reduction in the availability of food. In fact, the long nights of winter frequently bring feasts and more alcohol consumption. Women spend more time around food preparation than men, and this contributes to high rates of obesity. Much has been written about the obesity epidemic in the United States, and there is no indication that the trend is slowing.

Combating obesity will require a dedicated public health effort. Taxing high-calorie/low-nutrition foods, reducing subsidies for high fructose corn syrup, and promoting physical education in schools are interesting ideas to combat child obesity. But we all know that weight loss through diet is extremely difficult for adults, and that even when weight loss does occur, most fail to maintain a normal body weight. Among the many complications of obesity, type 2 diabetes is one of the principle drivers of high health care costs. Therefore, strategies that could reduce the chance that an obese individual will develop diabetes should not only improve the health of that individual, but also help stabilize health care spending.

Several important lessons emerge from the SOS. First, the risk of developing type 2 diabetes is substantially reduced by bariatric surgery. This finding was robust, as the surgical cohort was actually less healthy than the control group at baseline. The authors conducted a sensitivity analysis to compensate for the large study dropout (not surprising in a 15-year study) with no change to the overall conclusion that bariatric surgery reduces the chance of developing diabetes.

Next, bariatric surgery is far more effective than usual care in promoting weight loss. Subjects in the bariatric surgery group had an average maximal weight loss of 31 kg after 1 year. Although partial weight regain then occurred, the average weight loss from baseline values at 10 years and 15 years was approximately 20 kg. Compare this to the control group where mean weight changes never exceeded 3 kg in weight gain or weight loss. Even among those control subjects who sought additional professional help (54%), the mean weight change at year 2 was only a loss of 0.6 kg. Those who did not receive this help gained 1.4 kg! It is important to note that the magnitude of obesity was not associated with the reduction in risk; the incidence of type 2 diabetes and the preventive effect of bariatric surgery were similar among participants with a BMI at or below the median of 40.8 and those with a BMI above the median. In contrast, patients with an elevated fasting blood sugar at baseline appeared to benefit the most.

Finally, in a system of socialized medicine, the Swedes feel it is cost effective to provide surgical treatment for obesity. A recent review by Picot et al found that the incremental increased cost of bariatric surgery in the U.K. health system was negligible at 5 years and offset by savings over 20 years in patients with type 2 diabetes and class 2 obesity.1 Although the SOS authors did not conduct a cost analysis, the new results from SOS suggest that cost savings also may occur in obese individuals with elevated fasting glucose, regardless of BMI.

So our role is to advise our patients. Find the trusted resources in your area (or a nearby city) for referral to a bariatric surgery specialist in a comprehensive weight loss practice. When your next obese patient presents (should be tomorrow since one-third to one-half of your patients are obese), consider taking a moment to discuss their past experience with weight loss programs and the long-term success and potential benefits of bariatric surgery (particularly if their fasting glucose is elevated). As a trusted health care provider, your input just might open the conversation and help save their life.


1. Picot J, et al. Weight loss surgery for mild to moderate obesity: A systematic review and economic evaluation. Obes Surg 2012;22:1496-1506.