Resting energetic adaptations over the course of a 10-month multidisciplinary weight loss intervention in adolescents with obesity: The POWELL-2 project

BACKGROUND: Childhood obesity interventions have shown modest and often unsustainable effects, with frequent weight regain driven by physiological and behavioral compensatory mechanisms. While nutritional adaptations have been relatively well described, energetic adaptations remain insufficiently explored in pediatric populations. This study aimed to investigate the temporal dynamics of resting energy expenditure (REE), substrate oxidation, thyroid hormones, leptin concentrations, and adaptive thermogenesis (AT) throughout a 10-month weight loss intervention in adolescents with obesity. METHODS: Forty adolescents with obesity (13.9 ± 1.4 years; 20 boys) were recruited from a pediatric rehabilitation center and participated in a 10-month multidisciplinary intervention combining physical activity, nutritional education, and psychological support. Participants completed up to nine assessment visits at 4-5-week intervals. At each visit, anthropometry (weight, height, BMI z-score), fasting REE, substrate oxidation (indirect calorimetry), and blood sampling (TSH, triiodothyronine, thyroxine, leptin) were performed. Body composition was assessed by DXA at baseline, mid- and post-intervention. RESULTS: Among the 38 adolescents analyzed, the intervention induced significant changes in body composition, with a reduction in fat mass and BMI z-score over time (all p < 0.001) and a transient increase in fat-free mass (FFM) (p < 0.001), while body weight initially decreased (p < 0.040) before partially increasing at later stages (p ≤ 0.001). REE remained unchanged throughout the intervention, and no statistically significant difference between REEm and REEp (AT) was not observed, while respiratory quotient increased significantly (p < 0.001) over time. CONCLUSION: This longitudinal study reveals that, despite moderate weight loss, REE remained stable and AT was not clearly apparent, while the shift toward greater carbohydrate oxidation indicates ongoing and dynamic metabolic remodeling. Overall, these exploratory findings may suggest that metabolic adaptations to weight loss may be more variable than previously assumed, although confirmation in larger cohorts is still required.