Very-low-calorie diet: a quick therapeutic tool to improve β cell function in morbidly obese patients with type 2 diabetes

Background: Caloric restriction in obese diabetic patients quickly improves glucose control, independently from weight loss. However, the early effects of a very-low-calorie diet (VLCD) on insulin sensitivity and insulin secretion in morbidly obese patients with type 2 diabetes are still unclear. Objective: The objective was to study the relative contributions of insulin sensitivity, insulin secretion, or both to improvement in glucose metabolism, after 1 wk of caloric restriction, in severely obese diabetic patients. Design: Hyperglycemic clamps were performed in 14 severely obese (BMI, in kg/m2: .40) patients with type 2 diabetes in good glucose control (glycated hemoglobin , 7.5%) before and after 7 d of a VLCD (400 kcal/d). Results: The VLCD caused a 3.22 6 0.56% weight loss (P , 0.001), 42.0% of which was fat loss, accompanied by decreases in fasting plasma glucose (P , 0.05) and triglycerides (P ,0.01). In parallel, the Disposition Index, which measures the body’s capability to dispose of glucose load, increased from 59.0 6 6.3 to 75.5 6 6.3 mL min21 m22 body surface area (P , 0.01), because of improvements in indexes of both first- and second-phase insulin secretion (P , 0.02), but with no changes in insulin sensitivity (P =0.33). Conclusion: The marked improvement in metabolic profile, observed in severely obese patients with type 2 diabetes after a 7-d VLCD, was primarily due to the amelioration of b cell function, whereas no contribution of insulin sensitivity was shown.