Long‐Term Effect of a Hospital‐Based Intervention Program on <scp>BMI</scp> Trajectories in Danish Children and Adolescents With Overweight and Obesity: A 6‐Year Follow‐Up

Childhood obesity is associated with adverse health and psychosocial outcomes, often persisting into adulthood. Hospital-based lifestyle interventions may provide intensive support, but evidence on long-term effectiveness is limited. To evaluate changes in Body Mass Index z-score (BMIz) among children and adolescents with overweight and obesity participating in a hospital-based intervention compared to matched controls. This matched prospective cohort study includes children and adolescents aged 5-15 years. The intervention consisted of a family-centered hospital-based lifestyle program focusing on diet, physical activity, sleep and screen time management. Controls were matched on age, sex, weight category, and calendar year. BMI trajectories were analyzed using mixed effects models with linear splines, adjusting for socioeconomic factors from national registries. A total sample size of 1897 children and adolescents was included (325 intervention, 1572 controls). The intervention group achieved a higher reduction in BMIz during the first 6 months (-0.74 SD/years, 95% CI: -0.89; -0.60) and up to 12 months (-0.31 SD/years, -0.45; -0.16), compared to controls. From 12 to 36 months, a rebound in BMIz occurred (0.14, SD/years, 0.10; 0.17), and continued to rise through 72 months. The intervention was associated with improvements in BMIz up to 12 months after the intervention. However, the effects were not sustained at 6 years of follow-up. Trial Registration: Clinicaltrials.Gov identifier: NCT05790174.