Reference: Ann Surg 2015 Mar;261(3):421 (level 2 [mid-level] evidence)
Standard medical treatments of type 2 diabetes such as medication, dietary advice, and exercise recommendations have largely fallen short in curbing the disease, with only about 40% of patients achieving glycemic control. Bariatric surgery, while primarily used for weight loss, has also been found to increase remission rates of type 2 diabetes in patients with comorbid severe obesity (body mass index [BMI] >35 kg/m2), leading the American Diabetes Association (ADA) to recommend its use in these patients, especially if medication and behavioral treatments have failed to achieve glycemic control (ADA Grade B; Diabetes Care. 2016;39 Suppl 1(January):S1-S112). The largest proportion of patients with type 2 diabetes, however, have a BMI between 30 - 34.9 kg/m2, and the role of bariatric surgery for these patients is not well-established. Given the increased risk for all-cause mortality as well as vascular, cancer, and renal-related mortality, plus many other neurologic, gastrointestinal, infectious, and mental health-related morbidities in patients with type 2 diabetes (N Engl J Med. 2011;364(9):829-841), it is imperative that we find therapies to improve remission rates in these patients. The demonstrated efficacy of bariatric surgery in patients with diabetes and morbid obesity raises the question: should bariatric surgery should be routinely considered for non-morbidly obese patients with diabetes?
To investigate this question, a systematic review identified 7 randomized controlled trials and 6 observational studies comparing the diabetic remission rates with bariatric surgery to those of medical treatment in 818 patients with type 2 diabetes. Inclusion criteria stipulated that study treatment groups have mean BMIs < 40 kg/m2. Nine of the included studies had patients with mean BMIs < 35 kg/m2; the remaining 4 trials included patients with mean BMI 35-37 kg/m2. Diabetic remission was reported in eight of the trials and was defined as hemoglobin A1c < 7 or fasting glucose ≤ 126 mg/dL without the need of antidiabetic medications. Follow-up periods ranged from 12-36 months. Both medical and surgical management varied among trials: medical treatments included guideline-driven antidiabetic medication, weight management, and lifestyle modification, while surgical methods included gastric band, biliopancreatic diversion, sleeve, or Roux-en-Y bypass. The review is limited by incomplete quality assessment criteria, which did not account for allocation concealment.
The overall meta-analysis of 8 studies with 532 patients demonstrated that bariatric surgery was associated with higher diabetic remission rates than medical therapy alone (odds ratio (OR) 14, 95% CI 6.7-29.9, P<0.001, NNT 2-7 with a 3.4 % remission rate in controls), though results were limited by moderate statistical heterogeneity. Results were consistent in separate meta-analyses of 5 randomized trials with 399 patients, which was limited by substantial statistical heterogeneity, and 3 observational studies with 133 patients. In a subgroup analysis of patients with a BMI < 35 kg/m2, the outcome was similar (OR 21.8, 95% CI 7.7 to 61.6, P<0.001, NNT 2-6). Compared to medical treatment, bariatric surgery was also associated with statistically significant improvements in hemoglobin A1c levels and BMI in analyses of 13 studies with 766 patients, reduced rates of arterial hypertension in analysis of 7 studies with 463 patients, and dyslipidemia in analysis of 7 studies with 460 patients.
Bariatric surgery appears more likely to induce remission of type 2 diabetes, improve glycemic control, and decrease body mass index in patients with type 2 diabetes and non-morbid obesity in the short term compared to medical management alone. These results are compelling, helpful for clinicians referring for surgical intervention, and might even encourage insurance companies to assist with the procedural cost in this patient population. Additionally, these outcomes support the American Association of Clinical Endocrinologists/Obesity Society/American Association of Metabolic and Bariatric Surgery (AACE/OS/ASMBS) recommendations of 2013 (Obesity (Silver Spring). 2013 Mar;21 Suppl 1:S1-27) to offer bariatric surgery to this patient population. Future randomized controlled trials evaluating the effect of bariatric surgery on long-term complications of diabetes will likely contribute to future changes in the management of type 2 diabetes.
For more information, see the Diabetes mellitus type 2 in adults and Bariatric surgery topics in Dynamed Plus. DynaMed users, see the Diabetes mellitus type 2 in adults and Bariatric surgery topics in Dynamed Classic.