Background/Objectives: Body composition and protein-energy partitioning changes are important factors of body weight regulation, but have not been studied in the context of clinical obesity treatment setting. Thus, the aim of the present study was to investigate the pattern of body weight loss, body composition, and energy partitioning changes during a 9-month multidisciplinary weight loss program and 4-month follow up and to test the associations among these changes in adolescents with severe obesity. Subjects/Methods: Twenty-five adolescents (14.1 ± 1.5 years old; 13 girls) with severe obesity joined a pediatric obesity center for a 9-month inpatient multidisciplinary weight loss program. All participants performed body composition assessment (i.e. fat mass-FM, and fat-free mass-FFM) and completed a 36-h session in indirect calorimetric chamber before the start (T0), at the end of the intervention (T1) and 4 months follow-up to the intervention (T2). The protein-energy partitioning (P ratio) was calculated as urinary nitrogen loss/total energy expenditure over 24 hours. Interventions: 9-month individualized multidisciplinary weight loss program consisting of lifestyle education, psychological support, physical activity, and dietary intervention. Results: Initial P ratio was positively associated with changes in body weight from T0 to T1 (p = 0.038). The changes in FFM/FM were negatively associated with body weight changes in boys (p = 0.006) from T0 to T1 and in girls (p < 0.001) from T1 to T2. Urinary nitrogen excretion (p < 0.001) and total energy expenditure (p < 0.001) significantly decreased during the weight loss program while the P ratio did not significantly change. Conclusion: The present results suggest that baseline and changes in energy partitioning may be associated with changes in body weight in adolescents with severe obesity. In addition, sexual dimorphism in these patterns of change suggest the need for specific dietary and physical activity strategies in boys and girls to optimize body weight loss and to prevent or slow weight regain.
