All children should have the opportunity to grow up healthy regardless of who they are and where they live. This is not the case today – 1 in 5 children live with overweight or obesity, with strong socioeconomic disparities in health outcomes¹.

The Childhood Obesity Prevention Initiative under Cities for Better Health aims to accelerate the prevention of childhood obesity in disadvantaged, urban communities globally. The initiative has been launched in six cities across Brazil, Canada, France, Japan, South Africa, and Spain.

Guided by a global evidence-based framework, coalitions of cross-sector partners in each city will co-design, implement, and evaluate packages of holistic interventions to improve child health outcomes.​ Intervention packages must target children aged 6-13 and align with four principles:

1. Dual focus on diet and physical activity: Intervention packages must address both key behavioural risk factors to increase potential impact^2,3.

2. Multi-level approach: Interventions should work at multiple levels of society, from structural changes to individual support.

3. Community-driven design: Interventions must be designed and implemented in collaboration with local stakeholders to ensure localisation and support long-term sustainability.

4. Equity oriented approach: Interventions should target disadvantaged groups and areas to promote equitable outcomes.

For children ages 6-13, within 24 months of initiating interventions, the initiative aims to:

• Positively affect dietary quality and physical activity levels
• Improve health-related quality of life, including psychological, psychosocial and social health, and school functioning
• Advance healthy weight, including reducing BMI for children living with overweight or obesity, maintaining BMI for children with a normal weight status, and/or reducing the proportion of children living with overweight or obesity.
  

Based on these objectives, a set of success metrics has been defined. A controlled evaluation design will be used to measure impact using a repeated cross-sectional study with a comparison group.

• Controlled - Local coalitions define a set of intervention areas (distinct geographical units within the city, like neighbourhoods) and comparable control areas.
• Repeated - In these areas, data is collected on a set of success metrics at baseline (before introducing the interventions), 10-12 months after initiation, and 20-24 months after initiation.
• Cross-sectional - Data is collected from a cross-section of children at each of the three points, within the same areas.
• Study - After each of the three data collections, analyses are conducted to compare results between control areas and areas that receive interventions.

Applying the following principles, the study design is statistically powered for country-level analyses to detect change in mean BMI of 0.3 kg/m² after 24 months, while at the global level (aggregating across all six countries), it is possible to detect a change in mean BMI of 0.13 kg/m².

In each country, at each time point, data must be collected:

1. On at least 2,000 children at each time point

2. From at least 20 clusters (e.g., schools), each with minimum 100 children

3. From at least 10 intervention areas and 10 control areas 

Ultimately, the Childhood Obesity Prevention Initiative aims to:

• Establish world-leading, impactful, and scalable community-based interventions for the prevention of childhood obesity in disadvantaged communities.
• Leverage the evidence generated as a call to action for decision makers and investors locally and globally to advance obesity prevention through whole-of-society partnerships.
  
• Leverage the learnings generated as guidance to city and community leaders around the world on how to design, implement, measure, and sustain effective interventions for child health.
  

Childhood obesity is a complex problem shaped by a broad range of biological, environmental and socioeconomic factors. Overweight and obesity affect more than 390 million children and adolescents aged 5–19, representing 20% of all children in this age group¹. Childhood obesity increases the risk of early onset of type 2 diabetes and is a strong predictor of adult obesity⁴. Children from lower socioeconomic backgrounds tend to face higher risks of developing obesity^5,6,7.