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

Background: The recent worldwide increase in the prevalence of childhood ob esity may be due in part to a decrease in children's physical activity leve ls. Objective: The current study of children in the years just before puberty a imed to 1) measure total energy expenditure (TEE) by use of the doubly labe led water (DLW) method, 2) determine the proportion of TEE related to physi cal activity, 3) investigate the relations between measures of physical act ivity and body fatness, and 4) investigate possible sex differences in thes e 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 (<(x)overbar>+/- SD). Fat-free mass, a nd hence fat mass, was derived from the O-18 dilution space. Resting energy expenditure (REE) was calculated with use of the Schofield equations. Phys ical activity level was calculated as TEE/REE. Results: Mean TEE in both boys (7871 +/- 1135 kJ/d) and girls (7512 +/- 119 5 kJ/d) was significantly different (P<0.0001) from FAO/WHO/UNU recommendat ions (13% and 9% lower, respectively). There was no significant difference in physical activity level between boys (1.69<plus/minus>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 per centage of body fat (r=-0.50, P<0.0001). Conclusions: In boys but not girls, percentage of body fat is inversely ass ociated with physical activity level. Physical activity is one factor contr ibuting to body fatness in boys, but additional factors may influence the s ize of the fat stores in girls.