Racial differences in energy expenditure and aerobic fitness in premenopausal women

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Abstract
Background: Aerobic fitness, or maximal oxygen uptake (V̇O2max), and energy expenditure (EE) may be lower in African Americans than in whites. Objective: The objective of this study was to compare sleeping EE (SEE), resting EE (REE), free-living total EE (TEE), and V̇O2max in African American and white women after adjustment for body composition and free-living activity-related energy expenditure (AEE). Design: Eighteen African American and 17 white premenopausal women were matched for weight, percentage body fat, and age. SEE and REE were measured in a room calorimeter and V̇O2max was measured on a treadmill. Fat-free mass (FFM) and fat mass (FM) (4-compartment model), AEE (doubly labeled water and SEE), and regional lean tissue (dual-energy X-ray absorptiometry) were used as adjustment variables in SEE, REE, TEE, and V̇O2max comparisons. Results: The African American women had significantly more limb lean tissue and significantly less trunk lean tissue than did the white women. The African American women also had significantly lower SEE (6.9%), REE (7.5%), TEE (9.6%), and V̇O2max (13.4%) than did the white women. Racial differences persisted after adjustment for V̇O2max, AEE, FFM, and limb lean tissue but disappeared after adjustment for trunk lean tissue. The V̇O2max difference was independent of all body-composition variables and of AEE. Conclusions: African American women had lower aerobic fitness than did white women, independent of differences in lean tissue or AEE. Diminished racial differences in SEE, REE, and TEE after adjustment for trunk lean tissue suggest that low EE in African American women is mediated by low volumes of metabolically active organ mass.