Examining the roles of body composition, energy expenditure and substrate metabolism in the control of daily energy intake in adolescents with obesity.

Background: The implication of body composition and energy metabolism in the control of human energy intake (EI) has been well described in adults, remaining however unexplored in adolescents with obesity. The aim of this study was to question the role of body composition, energy expenditure (EE) and substrate metabolism in the control of EI of adolescents with obesity.

Methods: Ad libitum 24-h EI, body composition (Dual X-ray absorptiometry), Resting Metabolic Rate (RMR, indirect calorimeter) where measured and Total EE obtained during a 36-h stay in metabolic chambers in 26 adolescents (14.1 ± 1.5 years; 14 girls) with severe obesity.

Results: The mean body weight and Body Mass index were 92.2 ± 17.2 kg and 33.98 ± 4.14 kg.m^-2 respectively. 24-h EI was positively correlated with body weight (rho = 0.597, p = 0.014), Fat Free Mass (FFM) kg (rho = 0.576, p = 0.019), 24-h Total EE (TEE (rho =0.675, p < 0.001)), RMR (rho =0.632, p = 0.005), 24-h Carbohydrate (CHO) oxidation rates (rho = 0.716, p < 0.001), and urinary nitrogen excretion (rho =0.28, p < 0.001). According to the path analysis FFM (kg) but not Fat Mass (FM) (kg) was positively correlated with RMR, with direct effects of 0.87 (p < 0.001) and 0.027 (p = 0.74) respectively. The effect of FFM on 24-h EI was mediated by RMR (96% of the effect), while the effect of FM on 24-h EI was also mediated by RMR (67% of the effect).

Conclusions: The present study provides the first evidence regarding the role of RMR as a main tonic signal of appetite control mediating the effect of body composition and mainly FFM (over FM) on daily EI in adolescents with obesity. It also suggests for the first-time relationships between 24-h CHO and protein oxidation and daily EI in this population.