Caloric Restriction and Weight Loss Are Primary Factors in the Early Tissue-Specific Metabolic Changes after Bariatric Surgery.

OBJECTIVE To evaluate changes in insulin sensitivity, hormone secretion, and hepatic steatosis immediately after caloric restriction, vertical sleeve gastrectomy (VSG), and Roux-en-Y gastric bypass (RYGB). RESEARCH DESIGN AND METHODS Obese subjects were assessed for: 1) insulin sensitivity by hyperinsulinemic-euglycemic clamp with glucose tracer infusion, 2) adipokine concentrations by sampling serum and subcutaneous adipose interstitial fluid, and 3) hepatic fat content by magnetic resonance imaging before and 7-10 days after VSG, RYGB, or supervised caloric restriction. RESULTS Each group exhibited an approximately 5% total body weight loss, accompanied by similar improvements in hepatic glucose production and hepatic, skeletal muscle, and adipose tissue insulin sensitivity. Leptin concentrations in plasma and adipose interstitial fluid were equally decreased and reductions in hepatic fat were similar. CONCLUSIONS The improvements in insulin sensitivity and adipokine secretion observed early after bariatric surgery are replicated by equivalent caloric restriction and weight loss.