A coherent family support model (Co-Fam) for preventing and treating childhood overweight and obesity: protocol for a randomized hybrid type 2 effectiveness-implementation trial.

backgroundSwedish child healthcare involves school health services, primary healthcare, and pediatric clinics. Family-based programs addressing child diet, eating behavior, parental feeding practices and physical activity show promise for preventing and treating overweight in children 2-12 years, but organizational gaps hinder coherent implementation of interventions. The novel Co-Fam model integrates two complementary programs: the universal Healthy School Start (HSS) family support program, delivered in schools during grade 1, and the targeted 12 months More and Less (ML) parental support program, provided through primary healthcare to treat children 6-12 years with overweight and obesity. ML consists of ten group sessions with parents, followed by individual booster sessions. The dual primary aim of this study is to evaluate the effectiveness of the ML program on child bodyweight development and to assess implementation outcomes fidelity, acceptability, feasibility and cost-effectiveness of the Co-Fam model.

methodsThe setting for this study is a municipality in Region Stockholm with high cultural diversity and health needs, which has been running the HSS program since 2022. In this hybrid type 2 effectiveness-implementation study with two parallel arms, children aged 6-12 years with overweight or obesity will be randomized to either the ML program or standard care. Primary effectiveness outcomes are BMI z-score and %IOTF-25 measured at baseline, three and 12 months. Secondary outcomes are waist-to-height-ratio, parental feeding practices, child physical activity, diet and eating behavior. Primary implementation outcomes are fidelity to the ML program assessed at three and 12 months. Acceptability and feasibility of the Co-Fam model will be assessed three to 12 months after start, through semi-structured interviews with parents and providers. A health economic evaluation will be conducted using a cost-utility design. DISCUSSION: We hypothesize that ML will be more effective than standard care in reducing overweight and obesity in children. The integration of the HSS and ML programs in the Co-Fam model is expected to enhance collaboration between school and healthcare and ensure early identification of at-risk families. The dual focus on effectiveness and implementation will inform the scalability and sustainability of the Co-Fam model with implications for policy and practice in child obesity prevention and management.

trial registrationThe trial was registered at Clinicaltrials.gov, September 11-2025, ID: NCT07158944.