Metabolic characterization of nondiabetic severely obese patients undergoing Roux-en-Y gastric bypass: Preoperative classification predicts the effects of gastric bypass on insulin-glucose homeostasis

Introduction: Obese individuals may have normal insulin-glucose homeostasis, insulin resistance, or diabetes mellitus. Whereas gastric bypass cures insulin resistance and diabetes mellitus, its effects on normal physiology have not been described. We studied insulin resistance and β-cell function for patients undergoing gastric bypass. Methods: One hundred thirty-eight patients undergoing gastric bypass had fasting insulin and glucose levels drawn on days 0, 12, 40, 180, and 365. Thirty-one (22%) patients with diabetes mellitus were excluded from this analysis. Homeostatic model of assessment was used to estimate insulin resistance, insulin sensitivity, and β-cell function. Based on this model, patients were categorized as high insulin resistance if their insulin resistance was >2.3. Results: Body mass index did not correlate with insulin resistance. Forty-seven (34%) patients were categorized as high insulin resistance. Correction of insulin resistance for this group occurred by 12 days postoperatively. Sixty (43%) patients were categorized as low insulin resistance. They demonstrated an increase of β-cell function by 12 days postoperatively, which returned to baseline by 6 months. At 1 year postoperatively, the low insulin resistance group had significantly higher β-cell function per degree of insulin sensitivity. Conclusions: Adipose mass alone cannot explain insulin resistance. Severely obese individuals can be categorized by degree of insulin resistance, and the effect of gastric bypass depends upon this preoperative physiology. © 2007 The Society for Surgery of the Alimentary Tract.