DETERMINANTS OF RESTING ENERGY-EXPENDITURE IN YOUNG BLACK GIRLS AND YOUNG WHITE GIRLS

Objective: To identify determinants of resting energy expenditure (REE ) in black girls and white girls and to evaluate racial differences in REE. Study design: Cross-sectional study of 98 girls (47 black and 51 white girls), ages 6 to 16 years. Methods: Determinations of lean bod y mass, fat mass, and bone mass were made by dual-energy x-ray absorpt iometry. Measurements of REE were made with the DeltaTrac metabolic mo nitor. Subjects fasted at least 3 hours before testing, had rested 30 minutes before the test, and had not engaged in strenuous activity for the previous 12 hours. Pubertal maturation was assessed with a three- stage scoring method: (1) prepubertal, (2) pubertal, but premenarcheal , and (3) postmenarcheal. Results: There were no significant differenc es in height, weight, lean body mass, or fat mass between the black an d white subjects. Racial differences in fetal REE were also not signif icant, but REE standardized by weight was significantly greater in whi te girls (40.3 kcal/day) compared with black girls (35.5 kcal/day) (p = 0.001). Resting energy expenditure was positively and significantly correlated with all measures of body composition, Multiple regression analysis identified lean body mass, sexual maturation, and race as sig nificant main effects. After controlling for lean body mass and matura tion, black girls had significantly lower REE. The race-maturation int eraction was of borderline significance (p = 0.09); prepubertal black girls had significantly lower REE (1156 kcal/day) than prepubertal whi te girls (1399 kcal/day), but racial differences in stages 2 and 3 wer e not statistically significant. Conclusion: Lean body mass, maturatio n, and race are significant determinants of REE, Resting energy expend iture is significantly lower in black than white girls in the prepuber tal stage. The cause of this racial difference in REE is not known; it is not explained by differences in anthropometric variables. Racial d ifferences in REE could explain in part the earlier onset of puberty i n black girls compared with white girls and could be a factor in the d ifference in obesity in black and white women.