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Diabetes prevention

Swedish Obese Subjects: surgery prevents diabetes

The prospective, controlled Swedish Obese Subjects study involves over 4,000 subjects from the Scandinavian country.
Surgery reduced the risk of type 2 diabetes by 78%
Blood sugar level, not BMI, a better indicator of type 2 diabetes

Bariatric surgery is twice as effective as lifestyle changes at preventing type 2 diabetes in people who are obese, according to the latest paper from the Swedish Obese Subjects study. The outcomes revealed that surgery reduced the risk of type 2 diabetes by 78%, double the effect of diet and exercise alone.

"Bariatric surgery appears to be markedly more efficient than usual care in the prevention of type 2 diabetes in obese persons,” said co-author of the study, Dr Lena Carlsson, University of Gothenburg, Sweden. “It is well documented that bariatric surgery can help resolve type 2 diabetes, however this is the first study to suggest that such procedures can help prevent type 2 diabetes.”

The study was published in the New England Journal of Medicine.


Researchers led by Dr Lars Sjöström, Sahlgrenska University Hospital, Gothenburg, Sweden, analysed 1,658 patients who underwent bariatric surgery and 1,771 non-randomised, matched, prospective controls who received treatment of diet and exercise alone (matching performed on a group, rather than an individual level). None of the participants had diabetes at baseline. Patients in the bariatric-surgery cohort underwent banding (19%), vertical banded gastroplasty (69%), or gastric bypass (12%).

The participants were aged 37 to 60, with a BMI>34 in men and >38 in women. Despite matching, some baseline characteristics differed significantly between the groups; the baseline body weight was higher and risk factors were more pronounced in the bariatric-surgery group than in the control group.

Therefore, patients in the surgery group initially had a higher risk of developing diabetes than those in the control group.

At 15 years, 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.


During the follow-up period, type 2 diabetes developed in 392 participants in the control group and in 110 in the bariatric-surgery group, corresponding to incidence rates of 28.4 cases per 1,000 person-years and 6.8 cases per 1,000 person-years, respectively (adjusted hazard ratio with bariatric surgery, 0.17; 95% confidence interval, 0.13 to 0.21; p<0.001).

At 10 years, 28% of patients in the control group developed diabetes compared with 7% of the patients in the surgery group. At 15 years, 38% of patients in the control group developed diabetes compared with 13% in the surgery group.

For patients with impaired fasting glucose, bariatric surgery reduced the risk of developing diabetes by 87%.

“This risk reduction is at least twice as large as that observed with lifestyle interventions in moderately obese, pre-diabetic persons,” the authors noted. “The results are consistent with our preliminary observations published in 2004.”

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), indicating a patient’s blood sugar level before surgery is a better indicator than BMI of whether they would develop type 2 diabetes.

“The lack of BMI influence on prevention implies that anthropometric data are not useful in the selection of candidates for bariatric surgery,” the authors wrote.

Sensitivity analyses, including end-point imputations, did not change the overall conclusions. The postoperative mortality was 0.2%, and 2.8% of patients who underwent bariatric surgery required reoperation within 90 days owing to complications.

In the surgery group, the average weight loss at the 10- and 15-year mark was 20kgs (44lbs), compared with patients in the non-surgery group who stayed within 3kgs (7lbs) of their starting weight.


The authors concluded that bariatric surgery appears to be markedly more efficient than usual care in the prevention of type 2 diabetes in obese persons.

However, they are not suggesting bariatric surgery as a procedure for the prevention of type 2 diabetes, rather urging additional research.

“Our post hoc findings should be confirmed by prospective, controlled trials that are designed to study treatment effects on hard end points in predefined subgroups.”


In an accompanying commentary in the journal, Dr Danny Jacobs, Duke University, wrote that the concept of bariatric surgery preventing diabetes is “provocative and exciting,” although he adds that it would be “impractical and unjustified to think of doing it on millions of obese adults.”

Nevertheless, he states that this study could help doctors understand why surgery works and help identify the best candidates for the operation.

“The current study should provide an impetus to develop a more complete understanding of the mechanisms by which the various bariatric procedures exert their beneficial effects. Such understanding will be important because it will enable the identification of the persons who are the most appropriate candidates for surgery.”

The study was funded by the Swedish Research Council, the Swedish Foundation for Strategic Research to Sahlgrenska Center for Cardiovascular and Metabolic Research, the Swedish federal government, the VINNOVA-VINNMER program and the Wenner-Gren Foundations.

Further information about the SOS study (NCT01479452) can be found at the website.

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