Weight loss on low-fat vs. low-carbohydrate diets by insulin resistance status among overweight adults and adults with obesity: A randomized pilot trial

ObjectiveTo 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. MethodsSixty-one adults, BMI 28-40 kg/m(2), were randomized in a 2 x 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. ResultsBaseline % 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 7.46.0 (LF-IR), 10.4 +/- 7.8 (LF-IS), 9.6 +/- 6.6 (LC-IR), and 8.6 +/- 5.6 (LC-IS). No significant main effects were detected for weight loss by diet group or IR status; there was no significant diet x IR interaction. Significant differences in several secondary outcomes were observed. ConclusionsSubstantial weight loss was achieved overall, but a significant diet x IR status interaction was not observed. Opportunity to detect differential response may have been limited by the focus on high diet quality for both diet groups and sample size.