Objective: To test for differential weight loss response to low-fat (LF) vs. low-carbohydrate (LC) diets by insulin resistance status with emphasis on overall quality of both diets.
Methods: Sixty-one adults, BMI 28-40 kg/m2, were randomized in a 2 3 2 design to LF or LC by insulin resistance status in this pilot study. Primary outcome was 6-month weight change. Participants were characterized as more insulin resistant (IR) or more insulin sensitive (IS) by median split of baseline insulin-area-under-the-curve from an oral glucose tolerance test. Intervention consisted of 14 one-hour class-based educational sessions.
Results: Baseline % carbohydrate:% fat:% protein was 44:38:18. At 6 months, the LF group reported 57:21:22 and the LC group reported 22:53:25 (IR and IS combined). Six-month weight loss (kg) was 7.4 6 6.0 (LF-IR), 10.4 6 7.8 (LF-IS), 9.6 6 6.6 (LC-IR), and 8.6 6 5.6 (LC-IS). No significant main effects were detected for weight loss by diet group or IR status; there was no significant diet 3 IR interaction. Significant differences in several secondary outcomes were observed.
Conclusions: Substantial weigh t loss was achieved overall, but a significant diet 3 IR status interaction was not observed. Opportunity to detect differential response may have been limited by the focus on high diet qualit y for both diet groups and sample size.