Caloric Restriction Per Se Is a Significant Factor in Improvements in Glycemic Control and Insulin Sensitivity During Weight Loss in Obese NIDDM Patients

OBJECTIVE: To examine the effects of caloric restriction, independent of differences in weight loss, on improvements in glycemic control, fasting insulin, and insulin sensitivity. RESEARCH DESIGN AND METHODS: We randomized 93 obese type II diabetic patients to two different degrees of calorie restriction (1,674 or 4,185 kJ/day; 400 or 1,000 kcal/day) and compared the changes in fasting glucose, fasting insulin, and insulin sensitivity that resulted from a comparable reduction in body weight (11% of initial body weight). Insulin sensitivity was assessed using the minimal model analysis of frequently sampled intravenous glucose tolerance tests. RESULTS: Despite equal weight losses, subjects in the 1,674 kJ/day (400 kcal) condition had lower fasting glucose levels (7.61 vs. 10.13 mM, P = 0.03) and greater insulin sensitivity (1.79 vs. 1.13, P = 0.04) after weight loss than did subjects in the 4,185 kJ/day (1,000 calorie) condition. Subjects were restudied 15 weeks later when both groups were consuming a 4,185 kJ/day (1,000 kcal/day) diet. Subjects who increased from 1,674 to 4,185 kJ (400 to 1,000 calories) had worse fasting glycemic control in spite of continued weight loss, whereas subjects who remained on 4,185 kJ (1,000 calories) throughout had further improvements in both blood glucose and insulin sensitivity with increased weight loss. CONCLUSIONS: Both degree of calorie restriction and magnitude of weight loss have independent effects on improvements in glycemic control and insulin sensitivity.