Abstract P226: Improved Insulin Sensitivity with a Healthy Low Fat or a Healthy Low Carbohydrate Weight Loss Diet: A Twelve Month Randomized Trial

Abstract

Background: The abilities of healthy low fat (HLF) and healthy low carbohydrate (HLC) weight loss diets to improve insulin sensitivity over the long term are not well understood. Objective: To examine whether HLF and HLC weight loss diets improve insulin sensitivity over 12 months, and to determine if either diet is superior for these improvements. Methods: Healthy adults without diabetes, aged 18-50 years, BMI between 28 and 40 kg/m 2 , were randomized to HLF or HLC for 12 months (n = 609). Health educators delivered the interventions in 22 1-hr group classes. Dietary intake was assessed by three 24-hour recalls per time point. Glucose and insulin were measured at times 0, 30, 60, and 120 min during a 75-g oral glucose tolerance test. Indices of hepatic insulin sensitivity (homeostasis model assessment of insulin resistance; HOMA) and whole-body insulin sensitivity (Matsuda index and the plasma concentration ratio of triglyceride to HDL-cholesterol; TG/HDL-C) were measured. Data were collected at baseline and 12 months. Statistical analyses were performed on study completers. Results: Complete data were available for n = 193 for HLF, and n = 197 for HLC. BMI and all indices of insulin sensitivity were similar between groups at baseline (p > 0.25 for all). Macronutrient distributions at 12 months were 48% vs. 30% carbohydrate, 29% vs. 45% fat, and 21% vs. 23% protein for HLF and HLC, respectively. Changes in BMI (mean ± SEM) were similar between groups (HLF: 33.38 ± 0.28 to 31.48 ± 0.29; HLC: 33.01 ± 0.25 to 30.69 ± 0.28; p = 0.11). Improvements within each group were observed for HOMA (HLF: 3.81 ± 0.17 to 3.16 ± 0.12; HLC: 3.60 ± 0.13 to 3.00 ± 0.12), Matsuda index (HLF: 3.13 ± 0.14 to 3.92 ± 0.18; HLC: 3.10 ± 0.12 to 3.86 ± 0.14), and TG/HDL-C (HLF: 3.16 ± 0.17 to 2.74 ± 0.14; HLC: 2.91 ± 0.15 to 2.09 ± 0.14) (p < 0.001 for all). The improvement in TG/HDL-C was greater for HLC (p = 0.013), while the improvements in HOMA and Matsuda index did not differ significantly between groups (p > 0.75 for both). Conclusions: All indices of insulin sensitivity were improved with both diets after 12 months. Neither diet was superior for improving HOMA. The HLC diet was more effective for improving TG/HDL-C, but not the Matsuda index.