Diabetes and weight in comparative studies of bariatric surgery vs conventional medical therapy: a systematic review and meta-analysis

Abstract

We performed a meta-analysis of weight loss and remission of type 2 diabetes mellitus (T2DM) evaluated in randomized controlled trials (RCTs) and observational studies of bariatric surgery vs conventional medical therapy. English articles published through June 10, 2013 that compared bariatric surgery with conventional therapy and included T2DM endpoints with ≥12-month follow-up were systematically reviewed. Body mass index (BMI, in kilogram per square meter), glycated hemoglobin (HbA1C, in degree), and fasting plasma glucose (FPG, in milligram per deciliter) were analyzed by calculating weighted mean differences (WMDs) and pooled standardized mean differences and associated 95 % confidence intervals (95 % CI). Aggregated T2DM remission event data were analyzed by calculating the pooled odds ratio (POR) and 95 % CI. Random effects assumptions were applied throughout; I(2) ≥ 75.0 % was considered indicative of significant heterogeneity. Systematic review identified 512 articles: 47 duplicates were removed, 446 failed inclusion criteria (i.e., n < 10 per arm, animal studies, reviews, case reports, abstracts, and kin studies). Of 19 eligible articles, two not focused on diagnosed T2DM and one with insufficient T2DM data were excluded. In the final 16 included papers, 3,076 patients (mean BMI, 40.9; age, 47.0; 72.0 % female) underwent bariatric surgery; 3,055 (39.4; 48.6, 69.0 %) received conventional or no weight-loss therapy. In bariatric surgery vs conventional therapy groups, the mean 17.3 ± 5.7 month BMI WMD was 8.3 (7.0, 9.6; p < 0.001; I(2) = 91.8), HbA(1C) was 1.1 (0.6, 1.6; p < 0.001; I(2) = 91.9), and FPG, 24.9 (15.9, 33.9; p < 0.001; I(2) = 84.8), with significant differences favoring surgery. The overall T2DM remission rate for surgery vs conventional group was 63.5 vs 15.6 % (p < 0.001). The Peto summary POR was 9.8 (6.1, 15.9); inverse variance summary POR was 15.8 (7.9, 31.4). Of the included studies, 94.0 % demonstrated a significant statistical advantage favoring surgery. In a meta-analysis of 16 studies (5 RCTs) with 6,131 patients and mean 17.3-month follow-up, bariatric surgery was significantly more effective than conventional medical therapy in achieving weight loss, HbA(1C) and FPG reduction, and diabetes remission. The odds of bariatric surgery patients reaching T2DM remission ranged from 9.8 to 15.8 times the odds of patients treated with conventional therapy.

Fig. 1

Outcomes of the systematic review of the literature by record identification, screening, and analysis in the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) statement flow diagram

Fig. 2

Mean body mass index (BMI) reduction in bariatric surgery patients and conventional therapy patients by study design (randomized controlled trial vs observational)

Fig. 3

Mean glycated hemoglobin (HbA_1C) reduction in bariatric surgery patients and conventional therapy patients by study design (randomized controlled trial vs observational)

Fig. 4

The first three tables and corresponding forest plots summarize meta-analyses of the relative effects of bariatric surgery vs conventional therapy on body mass index (BMI), glycated hemoglobin (HbA_1C), and fasting plasma glucose (FPG). Each study contributing to a particular meta-analysis is represented by a single darkened square contained on the forest plot; the size of the square being proportional to the amount of weight the study was given during the calculation of the pooled summary estimate. The pooled estimate in the first three analyses is expressed as the weighted mean difference (WMD) and is represented by the diamond shape at the base of each forest plot. Two additional diamonds in each forest plot represent independent summary estimates for observational studies and randomized controlled trials. Negative WMD values indicate a treatment effect favoring surgical intervention. The fourth table (and forest plot) represents an analysis of the relative effects of surgery vs conventional therapy on T2DM remission. In this case, the summary estimate of effect is given by the pooled odds ratio (POR). Results favor surgery over conventional therapy when odds ratio values are greater than one

Fig. 5

Mean percent excess weight loss (%EWL) in bariatric surgery patients and conventional therapy patients by study design type (randomized controlled trial vs observational)