Restoration of Normal Insulinemia and Insulin Sensitivity in Hyperinsulinemic Normoglycemic Men by a Hypoenergetic High Monounsaturated Fat Diet

Purpose: To test the hypothesis that the macronutrient composition of hypoenergetic diets is an important consideration in weight-reducing regimens of hyperinsulinemic normoglycemic obese subjects. Design: A 4-week randomized dietary intervention trial. Subjects and Methods: Sixteen male obese hyperinsulinemic normoglycemic subjects were recruited and 15 completed the study. The participants were divided into two groups and fed hypoenergetic diets providing 80% of their resting energy expenditure (REE). One group received a high carbohydrate diet (HC) (60% carbohydrate, 20% fat, 20% protein as a percentage of dietary energy) and the other group received a high monounsaturated fat diet (HM) (35% carbohydrate, 45% fat and 20% protein). Anthropometry, body composition, REE, serum glucose, insulin and lipid analyses were performed before and after the feeding period. Results: The subjects on the HC diet achieved comparable weight loss but without restoration of normoinsulinemia and insulin sensitivity. Fasting insulin levels, insulin to glucose ratio, and Homeostatic Model & Assessment Index decreased to normal ranges and were significantly lower in the HM group as compared with the HC group. Similarly, insulin sensitivity score (Mffm/I) increased significantly on the HM diet. Waist circumference measurements showed a significantly higher decrease on the HM than HC diet, whereas body weight, percentage body fat, glucose, plasma lipids, and REE decreased to the same extent whether subjects were fed the HC or HM diet. Conclusions: In this study, feeding a HM diet was more effective than a HC diet for restoring normoinsulinemia and insulin sensitivity. Therefore, hyperinsulinemic normoglycemic obese subjects may benefit from a diet lower in carbohydrates and higher in monounsaturated fats for decreasing cardiovascular disease risk factors while achieving the desired weight reduction.