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 body mass, fat mass, and bone mass were made by dual-energy x-ray absorptiometry. Measurements of REE were made with the DeltaTrac metabolic monitor. 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 differences in height, weight, lean body mass, or fat mass between the black and white subjects. Racial differences in total REE were also not significant, but REE standardized by weight was significantly greater in white 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 significant main effects. After controlling for lean body mass and maturation, black girls had significantly lower REE. The race-maturation interaction was of borderline significance (p = 0.09); prepubertal black girls had significantly lower REE (1156 kcal/day) than prepubertal white girls (1399 kcal/day), but racial differences in stages 2 and 3 were not statistically significant.

CONCLUSION

Lean body mass, maturation, and race are significant determinants of REE. Resting energy expenditure is significantly lower in black than white girls in the prepubertal stage. The cause of this racial difference in REE is not known; it is not explained by differences in anthropometric variables. Racial differences in REE could explain in part the earlier onset of puberty in black girls compared with white girls and could be a factor in the difference in obesity in black and white women.