Resting energy expenditure and substrate utilisation rate in children with constitutional leanness or obesity

The influence of energy expenditure on body weight regulation, in the absence of organic disease, has never been studied in a paediatric population covering a broad range of body weights. The aim of this study was to investigate resting energy metabolism in children with constitutional leanness, normal body weight, or common obesity.

Fourteen children with constitutional leanness, 16 children with obesity, and controls were studied. Resting energy expenditure and postabsorptive substrate utilisation rate were measured by indirect calorimetry and body composition was assessed from skinfold thicknesses.

As compared to the predicted value calculated from the regression equation of resting energy expenditure on fat-free mass in the controls, resting energy expenditure was decreased in lean children (P=0.002), whereas no difference was found in obese children. In obese children and the overall population, fat mass was positively correlated with fat oxidation rate. In each group and in the overall population, fat oxidation rate was positively correlated to resting energy expenditure.

Constitutionally lean children have a low resting metabolic rate, probably adaptive in nature. In obese children, resting energy expenditure is increased in proportion to the fat-free mass, and fat balance is the main determinant of energy balance. These data suggest a constitutional regulation of body weight.