Design, Methods, and Pilot Baseline Results of the SEÍSMO Study: A School-Based Cluster Randomized Controlled Trial to Prevent Pediatric Obesity among Disadvantaged Communities in Spain

INTRODUCTION: Pediatric obesity is a major health issue with a growing worldwide trend since 1990. The present study aims to describe the design, methods, and pilot baseline results of a school-based obesity-prevention intervention implemented in disadvantaged communities. METHODS: The SEÍSMO study integrates two stages: the first stage includes baseline and follow-up assessments for 11,139 children aged 6-12, evaluated at baseline between 2020 and 2024 in 120 Spanish schools. The second stage is a 6-year cluster randomized controlled trial (RCT) that incorporated the learnings of the first stage to assess from 2024 to 2041 two primary outcomes (z-score body mass index and waist-to-height ratio) and several secondary outcomes (healthy lifestyles, quality of life, academic performance, psychosocial determinants, psychological resilience, and weight stigma) will be evaluated at 12, 24, 36, and 48 months. A sample size of 56 clusters and 4,760 participants is needed, assuming an attrition rate of 35% by 36 months post-baseline, but an oversampling will result in 10,080 participants. In this stage will involve three recruitment editions (2024-2025, 2025-2026, 2026-2027) and will incorporate children aged 3-12 located in Catalonia, Spain. The intervention includes a total of 50 specific action groups. In both study stages, a follow-up will be conducted at 18 years of age, involving a total of 21,219 children. CONCLUSIONS: SEÍSMO first-stage participants present prevalences of severe obesity and abdominal obesity of 5.4% and 31.3%, respectively. There is an urgent need to have effective obesity-prevention with the capacity to reduce the current inequalities.