Body Composition Changes During GLP-1 Receptor Agonist Therapy in Pediatric Obesity: A Pilot Study

Background and Objectives: GLP-1 receptor agonists (GLP-1 RAs) are effective weight-loss therapies, but data on body composition changes in pediatric obesity remain scarce. The primary objective was to evaluate the effects of GLP-1 RAs on body composition in children with obesity. Materials and Methods: We conducted a retrospective study of children with obesity evaluated at the National Institute for Mother and Child Health “Alessandrescu-Rusescu”, Bucharest, Romania, who initiated weekly injectable GLP-1 RA therapy (semaglutide) between January and December 2025. Patients were assessed at baseline and after a median follow-up of 5 months. Eight of ten participants with complete paired data were included in the final analysis; two were excluded because one was non-responder with weight gain and suspected non-compliance, while one responder could not maintain the standing position for bioimpedance measurement. Bioimpedance analysis and anthropometry were performed at both visits. Paired data were analyzed using Wilcoxon signed-rank tests. Results: Eight children (4 boys, 4 girls; mean age 14.9±1.8 years) completed the study. Significant Body Mass Index (BMI) Z-score improvements were observed (CDC: -0.14, p=0.012; WHO: -0.37, p=0.012), with median weight reduction of 4.75 kg (p=0.036). While absolute muscle mass showed non-significant change (-1.3 kg, p=0.362), predicted muscle mass percentage increased significantly (+1.9%, p=0.012), suggesting selective fat loss. Fat-free mass percentage increased (+2.0%, p=0.012) with reciprocal fat mass reduction (absolute: -3.85 kg, p=0.017; percentage: -2.0%, p=0.012). Fat-free mass index remained stable (-0.67 kg/m², p=0.161). No serious adverse events occurred. Sensitivity analysis (n=10) confirmed the robustness of the results, with BMI Z-score improvements remaining significant. Conclusions: GLP-1 RA therapy in children with obesity leads to notable improvements in BMI Z-scores and beneficial body composition changes, suggesting muscle mass preservation along with weight loss, even at submaximal doses. These findings support conducting a larger prospective study with body composition as the primary endpoint.