What Is Driving Energy Intake during Weight Loss? A Longitudinal Mediation Analysis in Adolescents with Obesity

Background: It has been posited that fat and lean tissues have a direct role in driving energy intake after significant weight loss, but this has yet to be demonstrated in adolescents with obesity. Objectives: The aim of this study was to elucidate the changes in direct and indirect associations between body composition, resting metabolic rate (RMR), and energy intake (EI) during weight loss after a multidisciplinary intervention in adolescents with obesity. Method: This was a secondary analysis of 26 adolescents with obesity (age: 14.1 ± 1.6 y; BMI z-score: 2.8 ± 0.8; 14 females) enrolled in a 9-mo inpatient multidisciplinary intervention and followed for 4 mo thereafter. Body composition, RMR, substrate metabolism, and EI over 24 h were measured on 3 separate occasions in a metabolic chamber at baseline (T0), postintervention (T1), and after follow-up (T2). Results: EI was significantly lower at both T1 (P < 0.001) and T2 (P < 0.001) after weight loss. Reductions in BMI z-score (P = 0.014) and protein metabolism (P < 0.001) with weight loss from T0 to T1 were negatively and positively associated with decreases in EI, respectively. Longitudinal mediation analyses revealed no direct effect of RMR change [β: 0.019; 95% highest posterior density interval (HPDI): −0.282, 0.344] or indirect effect of fat-free mass (FFM) change (β: −0.001; 95% HPDI: −0.264, 0.247) on EI change postintervention. However, the direct effect of fat mass (FM) change (β: 0.408; 95% HPDI: 0.128, 0.716) on EI change was significantly independent of changes in RMR and FFM. Conclusions: Although direct effects of FM and FFM independent of RMR were evident after weight loss, only changes in FM were associated with changes in EI. Improvement in whole-body protein turnover with weight loss could be relevant to regulation of dietary intake.