Background: Bariatric operations significantly improve glucose metabolism, decrease insulin resistance, and lead to clinical resolution of type II diabetes mellitus in many patients. The mechanisms that achieve these clinical outcomes, however, remain ill defined. Moreover, the relative impact of various operations on insulin resistance remains vigorously contested. Consequently, the purpose of this study was to compare directly the impact of laparoscopic Roux-en-Y gastric bypass (LRYGB) and laparoscopic adjustable gastric banding (LAGB) on hemoglobin A1c (HbA1c) levels and insulin resistance in comparable groups of morbidly obese patients.
Methods: Data were entered prospectively into our bariatric surgery database and reviewed retrospectively. Patients selected operations. Principle outcome variables were percent excess weight loss (%EWL), HbA1c, and homeostatic model assessment for insulin resistance (HOMA IR).
Results: The number of follow-up visits for 111 LAGB patients was 263 with a median of 162 days (17-1,016) and 291 follow-up visits for 104 LRYGB patients for a median of 150 days (8-1,191). Preoperative height, weight, body mass index, age, sex, race, comorbidities, fasting glucose, insulin, HbA1c, and HOMA IR were similar for both groups. In particular, the number of patients who were diabetics and those receiving insulin and other hypoglycemic agents were similar among the two groups. The LAGB patients lost significantly less weight than the LRYGB patients (24.6% compared to 44.0% EWL). LAGB reduced HbA1c from 5.8% (2-13.8) to 5.6% (0.3-12.3). LRYGB reduced HbA1c from 5.9% (2.0-12.3) to 5.4% (0.1-9.8). LAGB reduced HOMA IR from 3.6 (0.8-39.2) to 2.3 (0-55) and LRYGB reduced HOMA IR from 4.4 (0.6-56.5) to 1.4 (0.3-15.2). Postoperative HOMA IR correlated best with %EWL. Indeed, regression equations were essentially identical for LAGB and LRYGB for drop in %EWL versus postoperative HOMA IR.
Conclusion: Percent excess weight loss significantly predicts postoperative insulin resistance (HOMA IR) during the first year following both LRYGB and LAGB.