Energy expenditure in preadolescent African American and white boys and girls: the Baton Rouge Children's Study

Background: Low energy expenditure has been identified as a potential risk factor for body fat gain. Objective: The objective was to determine the relations between race, sex, body fat, and energy expenditure. Design: As part of the Baton Rouge Children's Study, energy expenditure was examined in 131 preadolescent African American and white girls and boys, further stratified as obese or lean. Total daily energy expenditure (TDEE) was measured by the doubly labeled water method. Resting metabolic rate (RMR) and the thermic effect of food were measured by indirect calorimetry. Fat-free mass and fat mass were measured by dual-energy X-ray absorptiometry. To account for differences in body size, energy expenditure variables were adjusted with the use of fat-free mass or fat-free mass and fat mass as covariates. Results: The African American children had lower TDEE and RMR than did the white children. A lower level of energy expended in physical activity by the African American girls and a lower RMR in the African American boys accounted for the racial differences in TDEE. The white boys had a higher RMR than did the white girls. The girls had a lower TDEE and expended less energy in activity than did the boys. Energy expended in activity was lower in the obese children. Conclusions: The African American children expended less energy than did the white children. The obese children spent less time engaged in activity or engaged in lower-intensity activity. Obese children may maintain their obese state by spending less time in physical activity, but they do not have a reduced RMR or thermic effect of food.