The weight-loss treatment program "ROS" is family-based and delivered by a multidisciplinary team of physicians, nurses, dieticians, and psychologists. The treatment is based on an individualized tailored plan made together with the family. The plan consists of dietary changes, more physical activity, regular weight checks, and motivational conversations. The program includes options of cooking classes, group session with a psychologist and participation in structured physical activity called "ROS sports" twice a week. Follow up visits are scheduled every 2-3 months at the different health care professionals.

The 'Overweight Clinic for Children and Adolescents' program at the municipal Health Center is based on the family-centered, multidisciplinary protocol developed by the Children's Obesity Clinic (TCOCT) at Holbæk Hospital. The intervention is individualized, informed by medical history and a structured questionnaire-based interview to identify behavioral and lifestyle changes needed to reduce the child's degree of overweight or obesity. The program consists of individual consultations every 6-8 weeks over approximately 12-18 months, with additional follow-up appointments as needed.

This treatment program is based on the Danish Health Authority's recommendations for lifestyle interventions. It follows a family-centered approach tailored to the family's everyday life and habits, focusing on sustainable changes in diet and physical activity. The program provides guidance on healthy eating, physical activity, and strategies for integrating these behaviors into daily routines.

The program included the entire family and began with school-based consultations delivered by health nurses during the first three months, followed by additional sessions at the municipal Health Center when needed. Families were offered 4-6 consultations within the first six months and follow-up sessions twice a year.

The primary objective is to investigate the changes in BMI z-score among children and adolescents with overweight or obesity who participated in a municipality-based or hospital-based weight-loss program, and whether existing characteristics of the child and parents at baseline modify this association. In addition we also want to characterize those who do not respond to treatment either because they gain or regain BMI z-score, or drop-out of the weight-loss program.