Relation of body mass index and body fatness to energy expenditure: longitudinal changes from preadolescence through adolescence

Background: Although it is widely accepted that weight gain results when energy intake exceeds energy expenditure (EE), how reduced EE contributes to the development of obesity remains unclear. Objective: We tested the hypothesis that reduced EE in the premenarcheal period in girls constitutes a risk factor for an increase in relative weight [body mass index (BMI) z score] and percentage of body fat (%BF) during adolescence. Design: We measured EE at study entry in 196 premenarcheal nonobese girls. Resting metabolic rate (RMR) was measured by indirect calorimetry. Total energy expenditure (TEE) was measured by the doubly labeled water method. Activity energy expenditure (AEE) was calculated from RMR and TEE. After the baseline study, girls were followed annually until 4 y after menarche ((x) over bar +/-SD: 7.1 +/- 2.6 y). At each visit, height, weight, and %BF by bioelectrical impedance were measured. Girls also completed annual food-frequency and activity questionnaires. Linear mixed effects modeling was used to evaluate the longitudinal relation between BMI z score and %BF and measures of baseline EE. Results: We found no significant relation in change in %BF with RMR, AEE, or TEE. We observed a small positive relation between BMI z score and AEE and TEE (P < 0.05) but no significant relation with RMR. When we stratified by parental overweight, the findings were unchanged for RMR. TEE and AEE were positively related to BMI z score in girls of overweight parents. Conclusions: Our findings suggest that EE in the premenarcheal period is not a risk factor for increases in %BF or BMI z score in girls during adolescence.