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.