Improved glucose metabolism after gastric bypass: evolution of the paradigm

BACKGROUND: Glucose metabolism is improved in patients with type 2 diabetes after Roux-en-Y gastric bypass (RYGB). OBJECTIVES: To quantify the relative contribution of calorie restriction, rerouting of nutrients, and adipose tissue reduction. SETTING: University Hospital. METHODS: Fifteen diabetic patients, (47±9 yr, body mass index 41.3±4.2 kg/m(2)) were randomized to a 2-week very low-calorie diet (VLCD) regimen or normal diet before RYGB. A euglycemic-hyperinsulinemic clamp, indirect calorimetry, and a standard meal test were performed prediet, postdiet (preoperatively), and 2 weeks and 12 months postoperatively. The primary outcome was whole-body insulin sensitivity (M) measured with the clamp 2 weeks postoperatively. RESULTS: In the VLCD group, after 2 weeks of calorie restriction, M improved (2.9±1.3 to 4.2±1.1 mg/kg/min, P = .005) with no further change at 2 weeks postoperatively. In the normal diet group 2 weeks postoperatively, M was similar to the VLCD group (4.7±1.7 versus 4.2±1.1, P = .61). One year postoperatively, M improved further in both groups. The improvement in insulin-stimulated glucose uptake after VLCD and RYGB was entirely accounted for by nonoxidative glucose disposal (NOGD), whereas weight loss at 1 year postoperatively was associated with an increase in NOGD and glucose oxidation. Postprandial glucose improved after VLCD (P