Childhood obesity is increasing rapidly in Pakistan, but there are no large, high-quality studies testing ways to prevent it in schools. This study aims to find out if a 9-month program involving health education, daily physical activity, parent workshops, and regular feedback via WhatsApp or SMS can reduce the number of primary school children who are overweight or obese.

The study is a cluster randomized controlled trial. A total of 26 primary schools in three cities of Punjab (Lahore, Sahiwal, Bahawalnagar) will be randomly assigned to either the intervention group (13 schools) or the control group (13 schools). Children in grades 3, 4, and 5 (aged 6-12 years) will take part.

In the intervention schools, children will receive 18 health education sessions, daily 45 minutes of physical activity, and monthly weight and height checks. Parents will attend three workshops and receive weekly messages and monthly feedback on their child's progress via WhatsApp or SMS. The control schools will continue their usual activities and receive the intervention materials after the study ends.

The main outcome is the change in the proportion of children who are overweight or obese from the start of the study to 9 months later. Secondary outcomes include changes in BMI z-score, waist circumference, physical activity, eating habits, and parents' knowledge. A follow-up assessment at 12 months will check if any benefits last.

Recruitment of schools and children began on January 8, 2026. This is the first cluster randomized trial of its kind in Pakistan. The results will help inform childhood obesity prevention policies in low- and middle-income countries.

Study Design: Two-phase, prospective, parallel-group, cluster-randomized controlled trial (cRCT) with an embedded mixed-methods process evaluation and longitudinal sustainability follow-up. Phase 1: 9-month primary efficacy trial. Phase 2: sustainability assessment at 12 months from baseline (3 months post-intervention).

Setting: 26 primary schools from three cities in Punjab, Pakistan: Lahore, Sahiwal, and Bahawalnagar. These cities represent the socioeconomic and cultural diversity of Punjab, the most populous province of Pakistan.

Randomization: Schools will be randomized 1:1 to intervention or control using computer-generated sequence, stratified by study site. An independent statistician will perform allocation concealment. Outcome assessors and the statistician will be blinded to group assignment. Participants, parents, and school personnel cannot be blinded due to the behavioral nature of the intervention.

Sample Size: 26 schools (13 intervention, 13 control), approximately 90 children per school, total 2,340 children aged 6-12 years in grades 3-5. Sample size calculation assumed a reduction in overweight/obesity prevalence from 36.7% to 26.7% (10% absolute reduction), 80% power, α=0.05, coefficient of variation k=0.15, and 20% attrition buffer.

Intervention (9 months): Developed using the Social Ecological Model and informed by a systematic review (PROSPERO CRD420251242889). Components include:

Child-focused: 18 biweekly sessions (40 min each) of health education (nutrition, physical activity, screen time reduction) and thematic workshops; daily 45 minutes of moderate-to-vigorous physical activity; monthly BMI measurement by trained staff; weekly self-weighing.

Parent-focused: Three workshops covering health messages, WhatsApp training, and feedback on child's progress; encouragement of 30-60 minutes of daily physical activity outside school.

mHealth component: Weekly automated WhatsApp/SMS messages with health tips and behavior tracking; monthly personalized feedback on child's BMI and behavior change. Tiered system for parents without smartphones (SMS or paper booklets).

Fidelity monitoring: Regular field observations, digital engagement logs, and process evaluation.

Control: Schools continue usual curriculum without any structured obesity prevention program. Routine physical education classes, standard school health checks if available, and no structured nutrition education or family engagement activities. After the 12-month follow-up, control schools receive intervention materials.

Outcomes:

Primary: Change in prevalence of overweight and obesity (WHO BMI-for-age z-score: overweight >+1 SD, obesity >+2 SD) from baseline to 9 months.

Secondary: Change in BMI z-score, waist circumference, body fat percentage, moderate-to-vigorous physical activity (days/week ≥60 min), daily screen time, dietary behaviors (sugar-sweetened beverages, fried foods, fast food), obesity-related knowledge (child), parental knowledge and self-efficacy, physical fitness (rope jumps, sit-ups, standing jump, shuttle run), and sustainability of BMI z-score change at 12 months.

Data Collection: Baseline (month 0), mid-point (month 6), post-intervention (month 9), sustainability follow-up (month 12). Anthropometric measurements (height, weight, waist/hip circumference, body fat percentage), blood pressure, physical fitness tests, and validated child/parent questionnaires.

Statistical Analysis: Intention-to-treat principle using generalized linear mixed models accounting for clustering. Primary outcome: binary prevalence analyzed with binomial distribution and logit link, adjusting for baseline values and stratification factors. Secondary continuous outcomes: mixed models with random intercept for school. Missing data <5% will use maximum likelihood; >5% sensitivity with last-value-carried-forward. Subgroup analyses by region, sex, maternal education, baseline BMI status, and primary caregiver. All tests two-sided α=0.05. Analysis will use SAS 9.4.

Process Evaluation: Concurrent mixed-methods evaluation guided by the EPIS framework to assess fidelity, dose, reach, adaptation, barriers, and facilitators. Quantitative metrics (reach, adoption, implementation fidelity, engagement logs) and qualitative interviews/focus groups with principals, teachers, and parents.

Ethics: Approved by Central South University Institutional Review Board (approval number XYGW-2026-18). Written parental consent and child verbal assent required. Data anonymized and securely stored. Study follows Declaration of Helsinki and local guidelines.

Trial Status: Recruitment began December 8, 2025. Planned primary completion September 8, 2026; study completion December 8, 2026.

Funding/Support: National Natural Science Foundation of China (as per proposal page 1). Sponsor: Central South University.

Inclusion Criteria:

• Children aged 6-12 years enrolled in grades 3, 4, or 5 of selected primary schools in Lahore, Sahiwal, or Bahawalnagar, Pakistan
• Written informed consent provided by parent or primary caregiver
• Child assent obtained
• Children without any medical conditions that prevent participation in physical activities

Exclusion Criteria:

• Medical history of heart disease, hypertension, diabetes, tuberculosis, asthma, hepatitis, or nephritis
• Obesity caused by endocrine diseases or side effects of drugs
• Abnormal physical development (e.g., dwarfism, gigantism)
• Physical deformity (e.g., severe scoliosis, pectus carinatum, limp, obvious O-leg or X-leg)
• Inability to participate in school sport activities
• Weight loss by vomiting or taking drugs during the past three months
• Participation in another obesity prevention or treatment program
• For schools: planned relocation or cancellation within the next two years

Individual participant data (IPD) that underlie the results reported in the main publication will be available after de-identification. Additional documents such as the study protocol, statistical analysis plan, and informed consent form will also be shared. Data will be available beginning 9 months and ending 36 months after article publication to researchers who provide a methodologically sound proposal. Proposals should be directed to the principal investigator (Qin jiabi, email: qinjiabi123@163.com. To gain access, requestors will need to sign a data access agreement.

IPD and supporting documents will be available beginning 9 months after publication of the main trial results and ending 36 months after article publication.

De-identified individual participant data and the supporting documents listed above will be made available to researchers who provide a methodologically sound proposal. Data will be shared for the purposes of meta-analysis, secondary research, or re-analysis. Requests should be directed to the principal investigator (Qin jiabi, email: qinjiabi123@163.com). Requestors will be required to sign a data access agreement to ensure data are used only for the agreed purpose and that no attempts are made to re-identify participants.

Participants, parents, teachers, and intervention providers cannot be blinded due to the behavioral nature of the intervention. Outcome assessors conducting anthropometric measurements (height, weight, waist circumference) will be blinded to school allocation. The statistician performing the final analysis will also be blinded. Data will be coded to protect blinding during analysis.