Total energy expenditure, body fatness, and physical activity in children aged 6–9 y

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Abstract
Background: The recent worldwide increase in the prevalence of childhood obesity may be due in part to a decrease in children's physical activity levels. Objective: The current study of children in the years just before puberty aimed to 1) measure total energy expenditure (TEE) by use of the doubly labeled water (DLW) method, 2) determine the proportion of TEE related to physical activity, 3) investigate the relations between measures of physical activity and body fatness, and 4) investigate possible sex differences in these relations. Design: The DLW technique was used to measure TEE over 10 d in 106 healthy children (52 boys) aged 7.8 ± 0.9 y (x̄ ± SD). Fat-free mass, and hence fat mass, was derived from the 18O dilution space. Resting energy expenditure (REE) was calculated with use of the Schofield equations. Physical activity level was calculated as TEE/REE. Results: Mean TEE in both boys (7871 ± 1135 kJ/d) and girls (7512 ± 1195 kJ/d) was significantly different (P < 0.0001) from FAO/WHO/UNU recommendations (13% and 9% lower, respectively). There was no significant difference in physical activity level between boys (1.69 ± 0.22) and girls (1.71 ± 0.23). In boys but not girls, physical activity level was inversely correlated with BMI (r = −0.37, P < 0.01), fat mass (r = −0.46, P < 0.005), and percentage of body fat (r = −0.50, P < 0.0001). Conclusions: In boys but not girls, percentage of body fat is inversely associated with physical activity level. Physical activity is one factor contributing to body fatness in boys, but additional factors may influence the size of the fat stores in girls.