Fangshan Active Nutrition Initiative

Study Design This is a two-arm, cluster-randomized controlled trial (cRCT) designed to evaluate the implementation and effectiveness of a multi-level, digital platform-based weight management intervention for school-aged children in Fangshan District, Beijing. The study consists of a 12-month active intervention period followed by an additional 12 months of follow-up, totaling 24 months of observation post-baseline.

Setting and Participants The study will be conducted in 10 primary schools in Fangshan District, Beijing, recruited through the Fangshan District School Health Care Center. Schools will be randomized (1:1 ratio) to either the intervention or control arm. Participants will be third-grade students (aged 8-9 years) at baseline.

Inclusion Criteria: Eligible students must provide signed informed consent from a parent or guardian and their own assent.

Exclusion Criteria: Students with pre-existing medical conditions that contraindicate physical activity or secondary obesity of known endocrine origin will be excluded from the analytic sample but may participate in the general program activities to avoid exclusion-based stigma.

InterventionThe intervention targets three levels-students, families, and schools-over one academic year. A digital platform embedded within WeChat serves as the central hub for knowledge dissemination, behavior monitoring, and automated feedback.

1. Student-level Interventions Health Education: Ten 40-minute classroom sessions delivered every 2-3 weeks, focusing on healthy weight maintenance, reducing sugar-sweetened beverages (SSBs), limiting sedentary behavior, and increasing physical activity. Sessions include interactive "hand-in-hand" homework assignments to be completed with parents.

Physical Activity Promotion: Targeted daily routines to achieve at least 60 minutes of moderate-to-vigorous physical activity (MVPA) at school, emphasizing outdoor activities and muscle/bone-strengthening exercises.

Monitoring: Monthly anthropometric measurements (height, weight, waist circumference, and body composition) conducted by trained school health staff, supplemented by weekly student self-weighing using classroom scales. 2. Family-level Interventions Parental Education: Two health education seminars per academic year (30-40 minutes each) and optional parent discussion forums to address implementation challenges.

Digital Engagement: Parents use the WeChat platform to: (a) receive regular push notifications of health education materials, (b) complete monthly behavioral questionnaires (diet, activity, sleep), and (c) view individualized monthly feedback reports comparing their child's BMI and behavioral progress against health standards.

Home Environment: Encouragement of home-based active play and parental modeling of healthy habits. 3. School-level Interventions Coordination: Designation of a school-level project coordinator to oversee logistics.

Environmental Changes: Integration of health sessions into the formal timetable and implementation of policies to limit the availability and consumption of SSBs and unhealthy snacks on campus.

Atmosphere: Classroom-based health promotion materials (e.g., posters, food environment labeling) and professional development for involved teachers.

Control Group Control schools will maintain their usual curriculum during the 12-month intervention period. Following the 24-month follow-up assessment, control schools will be provided with the intervention curriculum and relevant health education resources as an ethical cross-over.

Follow-Up and Data Collection Assessments will be conducted at baseline, 6 months, 12 months, and 24 months. Anthropometric \& Clinical: Height, weight, waist/hip circumference, blood pressure, and body fat percentage (via bioelectrical impedance analysis).

Physical Fitness: 1-minute rope skipping, 1-minute sit-ups, standing long jump, and endurance shuttle runs.

Questionnaires: Validated tools for students and parents assessing dietary habits, physical activity, sedentary time, and sleep quality.

Statistical Analysis and Sample Size Sample Size: Assuming a mean BMI reduction of 0.50 kg/m2 (SD: 1.40kg/m2), an intra-cluster correlation coefficient (ICC) of 0.03, and a two-sided significance level of 0.05. Accounting for a 10% attrition rate, a total of 135 students per school is required. With 10 schools (4 classes per school, approximately 35 students per class), the study targets a total sample of approximately 1,400 students, achieving 80% power.

Evaluation: Mixed-effects models will be used to analyze primary and secondary outcomes, accounting for school-level clustering and repeated measures.

Ethical Considerations The protocol and all materials have been approved by the Institutional Review Board of Peking University Health Science Center. Participation is strictly voluntary. Personal data will be anonymized, and protocols include specific measures to avoid weight-based stigma and ensure privacy during physical assessments.

Study Timeline Recruitment \& Baseline: March 2026 Active Intervention: March 2026 - March 2027 Follow-up Assessments: September 2026 (6m), March 2027 (12m), and March 2028 (24m) Analysis \& Publication: March 2027 - June 2028

• body fat percent (BFP) [Срок оценки: at the end of the 12-month intervention; at 24-month follow-up]
• Prevalence of Obesity among School-aged Children [Срок оценки: at the end of the 12-month intervention; at 24-month follow-up]
• Body Mass Index Z-score(BMI-z) [Срок оценки: at the end of the 12-month intervention; at 24-month follow-up]
• Waist Circumference [Срок оценки: at the end of the 12-month intervention; at 24-month follow-up]
• Children's Eating Behaviors [Срок оценки: at the end of the 12-month intervention]
• Time Spent in Physical Activity [Срок оценки: at the end of the 12-month intervention]
• Time Spent in Sedentary Behavior [Срок оценки: at the end of the 12-month interventionl]