Energy expenditure and physical activity of obese children: cross-sectional study.

OBJECTIVES To investigate the total daily energy expenditure and physical activity pattern of a group of obese and non-obese Hong Kong children. DESIGN Cross-sectional study. SETTINGS University teaching hospital, Hong Kong. PARTICIPANTS Eighteen obese children aged 6 to 17 years and 18 age- and sex-matched non-obese children in the local Hong Kong community. MAIN OUTCOME MEASURES Total daily energy expenditure and physical activity pattern were estimated for 3 days using heart rate monitoring. Body composition was measured by dual-energy X-ray absorptiometry. RESULTS In obese children, both total fat mass and fat-free mass were greater than in non-obese children. Total daily energy expenditure and its sleep and sedentary components were higher in absolute terms (by 42%, 43%, and 126%, respectively) for obese children. When normalised for body weight, the basal metabolic rate was no different between obese and non-obese children, while the total daily energy expenditure of the obese children was significantly lower (by 22%) than that of non-obese children. When normalised for fat-free mass, the basal metabolic rate and the sedentary component of total daily energy expenditure were significantly higher for obese children. Obese children spent 12% less time asleep, but 51% more time in sedentary activity and 30% less time physically active: a ratio of active-to-sedentary waking time of 0.6 for obese children and 1.9 for non-obese children. CONCLUSIONS Although the basal metabolic rate may be influenced by body composition, the finding of a normal basal metabolic rate when normalised for body weight suggests that an intrinsic difference of metabolic rate is not a major contributory cause of obesity. The study pointed particularly to the potential benefit of increasing physical exercise time relative to sedentary activities to reduce the prevalence of childhood obesity. Obese and non-obese children had similar basal metabolic rates when adjusted by fat-free mass and fat mass. Obese children spent more time in sedentary activities.