RESTING ENERGY-EXPENDITURE AND FOOD-INDUCED THERMOGENESIS IN OBESE CHILDREN

Nineteen overweight girls 14.54 +/- 0.38 years of age were studied. Results were compared with those obtained in eight age-matched (14.07 +/- 0.51 years) and sex-matched normal weight controls. Energy expenditure (EE) was determined using open-circuit indirect calorimetry at rest, both after a 12-h fast and after an oral sucrose load of 3 g/kg ideal body weight. Food-induced thermogenesis (FIT) was evaluated by computing the area under the curve of the EE response above resting energy expenditure (REE) during the first 3 h after the sucrose load, REE (kcal/day) was higher in the overweight patients (1,818 +/- 46 vs. 1,527 +/- 67; p = 0.002); REE standardized by fat-free mass (FFM) (kcal/kg FFM/day) was lower in obese children than in controls (35.2 +/- 1.0 vs. 44.9 +/- 1.9; p = 0.0001). A linear correlation between REE and FFM was evidenced in both controls and overweight subjects (r = 0.78 and 0.68, respectively; p = 0.05 and p < 0.001, respectively). Actual REE in the obese children was significantly lower than the value predicted by applying the regression equation of REE on FFM in controls to the actual FFM in obese children (paired t test; p = 0.003). FIT was identical in overweight and normal weight subjects, regardless of whether it was expressed in absolute value, as the percentage calorie intake, or standardized by FFM. However, obese children were assigned to two groups according to whether FIT was lower than the value in controls (group 1, <mean - 1 SD; n = 9) or at least equal to the value in controls (group 2, greater-than-or-equal-to mean - 1 SD, n = 10); the only feature that discriminated between these two groups was the presence or absence of a family history for obesity (FHO): FIT was significantly higher in obese children with a negative FHO than in obese children with a positive FHO. Our results support the presence of an energy metabolism disorder in some obese children and suggest that its cause may be constitutional in obese children with a positive FHO.