The impact of a low-carbohydrate (vs. low-fat) diet on fat mass loss in African American women is modulated by insulin sensitivity.

Objective: The objective of this study was to examine the independent and interactive effects of insulin sensitivity (S), the acute insulin response to glucose, and diet on changes in fat mass (FM), resting and total energy expenditure (REE and TEE, respectively), and mechanical efficiency, during weight loss, in African American women with obesity.

Methods: A total of 69 women were randomized to low-fat (55% carbohydrate [CHO], 20% fat) or low-CHO (20% CHO, 55% fat) hypocaloric diets for 10 weeks, followed by a 4-week weight-stabilization period (controlled feeding). S and acute insulin response to glucose were measured at baseline with an intravenous glucose tolerance test; body composition was measured with bioimpedance analysis at baseline and week 10; and REE, TEE, and mechanical efficiency were measured with indirect calorimetry, doubly labeled water, and a submaximal bike test, respectively, at baseline and week 14.

Results: Within the group with low S, those on the low-CHO diet lost more weight (mean [SE], -6.6 [1.0] vs. -4.1 [1.4] kg; p = 0.076) and FM (-4.9 [0.9] vs. -2.1 [1.0] kg; p = 0.04) and experienced a lower reduction in REE (-48 [30] vs. -145 [30] kcal/day; p = 0.035) and TEE (mean [SE] 67 [56] vs. -230 [125] kcal/day; p = 0.009) compared with those on the low-fat diet.

Conclusions: A low-CHO diet leads to a greater FM loss in African American women with obesity and low S, likely by minimizing the reduction in EE that follows weight loss.