Comparison of the effects on insulin resistance and glucose tolerance of 6-mo high-monounsaturated-fat, low-fat, and control diets

Abstract

BackgroundThe effect of dietary fat and carbohydrate on glucose metabolism has been debated for decades. ObjectiveThe objective was to compare the effect of 3 ad libitum diets, different in type and amount of fat and carbohydrate, on insulin resistance and glucose tolerance subsequent to weight loss. DesignForty-six nondiabetic, obese [mean (±SEM) body mass index (in kg/m2): 31.2 ± 0.3] men (n = 20) and premenopausal women (n = 26) aged 28.0 ± 0.7 y were randomly assigned to 1 of 3 diets after ≥8% weight loss: 1) MUFA diet (n = 16): moderate in fat (35–45% of energy) and high in monounsaturated fatty acids (>20% of energy); 2) LF diet (n = 18): low-fat diet (20–30% of energy), and 3) control diet (n = 12): 35% of energy as fat (>15% of energy as saturated fatty acids). Protein accounted for 15% of energy in all 3 diets. A 2-h oral-glucose-tolerance test (OGTT) was performed before and after the 6-mo dietary intervention. All foods were provided by a purpose-built supermarket. ResultsAfter 6 mo, the MUFA diet reduced fasting glucose (−3.0%), insulin (−9.4%), and the homeostasis model assessment of insulin resistance score (−12.1%). Compared with the MUFA diet, the control diet increased these variables [1.4% (P = 0.014), 21.2% (P = 0.030), and 22.8% (P = 0.015), respectively], as did the LF diet [1.4% (P = 0.090), 13.1% (P = 0.078), and 15.5% (P = 0.095), respectively]. No significant group differences were detected in glucose or insulin concentrations during the OGTT, in the Matsudas index, in body weight, or in body composition. ConclusionA diet high in monounsaturated fat has a more favorable effect on glucose homeostasis than does the typical Western diet in the short term and may also be more beneficial than the official recommended low-fat diet during a period of weight regain subsequent to weight loss. This trial was registered at clinicaltrials.gov as NCT00274729.