Fat oxidation in black and white youth: a metabolic phenotype potentially predisposing black girls to obesity.

INTRODUCTION: The prevalence of obesity is higher in Blacks with racial divergence in adiposity in girls starting during adolescence. Our hypothesis is that in Black children, puberty associated increase in fat oxidation is diminished and could play a role in predisposing to fat accretion triggered during puberty. Thus, we examined the relationships between race, pubertal development, and postabsorptive fat oxidation in youth. SUBJECTS AND METHODS: This was a cross-sectional design of healthy Black (n=50) and white (n=51) youth. Resting metabolic rate (RMR) and substrate oxidation rate were measured after an overnight fast with indirect calorimetry. Body composition was measured by dual-energy x-ray absorptiometry. RESULTS AND DISCUSSION: Within each race, RMR (kcal/kg fat free mass.min) was lower (puberty effect; P<0.05) in the pubertal vs. prepubertal group independent of gender. In girls, RMR was lower (race effect; P<0.05) in Blacks vs. whites. In girls but not boys, Blacks had lower (race effect; P=0.033) fat oxidation (micromol/kg fat free mass.min) compared with whites independent of pubertal status. Furthermore, the difference in fat oxidation between the prepubertal vs. pubertal groups tended to be greater (puberty x race interaction; P=0.089) in white girls (3.7+/-0.5 vs. 6.5+/-0.5) than in Black girls (3.4+/-0.6 vs. 4.5+/-0.5). These data suggest that the lower fat oxidation and RMR during puberty in Black girls could be a risk factor predisposing to obesity. This metabolic phenotype could potentially explain the divergence in adiposity in Black girls during adolescence against the backdrop of an obesogenic environment.