Methodology

Community-Based Multi-Component Intervention for Obesity Prevention in Young Adults (< 30 Years)

3.1 Study Design

3.2 Study Setting

• University campuses
• Workplaces and vocational training institutions
• Community health centres
• Faith-based community organizations

3.3 Study Population

3.3.1 Target Population

3.3.2 Inclusion Criteria

• Age 18–29 years (inclusive)
• Body Mass Index (BMI) ≥ 23 kg/m² (pre-obese or obese, WHO classification) or at least one obesity-related risk factor (sedentary behaviour, high dietary fat intake, family history of obesity or type 2 diabetes)
• Able to give written informed consent
• Resident in the study area for ≥ 6 months prior to enrolment
• Able to participate in physical activity (cleared by screening questionnaire or physician)

3.3.3 Exclusion Criteria

• Diagnosed eating disorder
• Pregnancy or intention to become pregnant during the study period
• Active pharmacological or surgical weight loss treatment
• Serious psychiatric illness or cognitive impairment that precludes meaningful participation
• Participation in another weight management program

3.4 Sample Size Calculation

3.5 Sampling and Randomization

3.5.1 Cluster Identification and Sampling

3.5.2 Randomization

3.5.3 Individual Recruitment within Clusters

3.6 The Multi-Component Intervention

3.6.1 Component 1 — Dietary Modification

• Weekly group nutrition education sessions (60 minutes/week for 12 weeks, then monthly booster sessions) delivered by a registered dietitian
• Topics: macronutrient balance, portion control, sugar-sweetened beverage reduction, fruit and vegetable intake, mindful eating
• Personalized dietary goal-setting using motivational interviewing techniques
• Distribution of culturally adapted healthy eating guides
• Dietary self-monitoring via a mobile application (food diary with feedback)

3.6.2 Component 2 — Structured Physical Activity

• Three supervised exercise sessions per week (45–60 minutes each), comprising aerobic training (moderate intensity, 150–300 min/week as per WHO guidelines) and progressive resistance training
• Sessions conducted at community venues by certified fitness instructors
• Unsupervised activity encouraged through a step-tracking wearable device or smartphone pedometer (daily step goal: 8,000–10,000 steps)
• Monthly fitness assessments to adapt exercise prescriptions

3.6.3 Component 3 — Behavioural and Psychosocial Support

• Bi-weekly group behavioural support sessions (45 minutes) using Cognitive Behavioural Therapy (CBT)-informed techniques: self-monitoring, goal setting, relapse prevention, stress management, and social support building
• Peer-support buddy system within clusters
• Digital engagement: weekly motivational SMS/push notifications, WhatsApp group for community peer exchange
• A brief screening for depression and anxiety at baseline; participants screening positive will be referred to community mental health services

3.7 Control Arm

• A single 1-hour health education session on general healthy lifestyle (delivered at baseline only)
• A printed copy of the national obesity prevention guidelines
• No structured dietary, physical activity, or behavioural sessions during the 12-month active phase

3.8 Data Collection

• T0 — Baseline (before randomization/intervention commencement)
• T1 — 12 months (end of active intervention)
• T2 — 18 months (6-month post-intervention follow-up)

3.8.1 Primary Outcome Measures

3.8.2 Secondary Outcome Measures

3.8.3 Process Evaluation Measures

• Intervention fidelity (session attendance registers, facilitator checklists)
• Participant satisfaction (exit questionnaires at T1)
• App engagement metrics (logins, diary entries per week)

3.9 Instruments and Validity

3.10 Statistical Analysis

3.10.1 Primary Analysis

• Analysis will be by intention-to-treat (ITT), including all randomized clusters regardless of adherence
• Missing data will be handled using multiple imputation by chained equations (MICE), assuming data missing at random (MAR)
• The primary comparison (change in BMI at 12 months, intervention vs. control) will use linear mixed-effects models accounting for:
  • Cluster-level random effect (to correct for intracluster correlation)
  • Baseline BMI, age, sex, and socioeconomic status as fixed covariates
  • Time × arm interaction term
• Results reported as mean difference with 95% confidence intervals and p-values; significance threshold α = 0.05

3.10.2 Secondary Analyses

• Secondary continuous outcomes (waist circumference, body fat %, lipid profile, dietary intake, physical activity, HRQoL) analysed using the same mixed-effects modelling approach
• Binary/categorical outcomes (proportion achieving ≥5% weight reduction) analysed by modified Poisson regression with robust variance estimation
• Subgroup analyses by sex, baseline BMI category (overweight vs. obese), and setting type (university vs. workplace vs. community centre) — exploratory, reported with appropriate caution

3.10.3 Economic Analysis (optional nested sub-study)

• Incremental cost-effectiveness ratio (ICER) per unit change in BMI and per QALY gained, adopting a societal perspective (informed by Yan et al., BMC Medicine, 2025 [PMID 41286848])

3.11 Ethical Considerations

• Full ethical approval will be sought from the relevant Institutional Review Board (IRB) / Research Ethics Committee prior to commencement
• All participants will provide written informed consent; consent for adolescents 18+ is self-consent
• Data confidentiality: all records will be de-identified and stored on password-protected, encrypted servers; access limited to the research team
• Voluntary participation: participants may withdraw at any time without penalty or loss of standard care
• Participants identified with significant cardiometabolic risk or mental health distress during screening will be referred to appropriate services
• The study will be registered on ClinicalTrials.gov (or equivalent international registry) and findings reported following the CONSORT extension for cluster-RCTs

3.12 Strengths and Limitations

• Cluster-RCT design minimises contamination and reflects real-world community delivery
• Multi-component approach addresses dietary, physical, and psychosocial determinants simultaneously
• Digital engagement tools (mobile app, wearables) enhance scalability and remote monitoring
• Process evaluation embedded within the design to assess fidelity and mechanisms

• Blinding of participants to allocation is not possible given the nature of behavioural interventions; outcome assessors will be blinded where feasible
• Self-reported dietary and physical activity data are subject to recall and social desirability bias
• Generalizability may be limited to urban/peri-urban settings in similar socioeconomic contexts
• Twelve months may be insufficient to capture the full trajectory of behavioural change and weight stabilization

Key References

1. Franco JV, Guo Y, Bongaerts B, et al. Multimodal health behaviour-changing interventions for adolescents living with obesity. Cochrane Database Syst Rev. 2025. [PMID 41410207]
2. Chen H, Hu P, Yang X, Li Y. The effect of online fitness combining dietary intervention on body composition, body shame and self-esteem in young adults: A randomized controlled trial. Nutrients. 2026. [PMID 42124061]
3. Yan S, Zhou S, Guo X, et al. Economic evaluation of a multi-component obesity prevention intervention in Chinese primary schools. BMC Med. 2025. [PMID 41286848]
4. Kelly A, Croker H, O'Neill R, et al. A systematic scoping review of adult obesity policy actions and weight-related services using the behaviour change wheel. BMC Public Health. 2026. [PMID 41612340]
5. Schwartz's Principles of Surgery, 11th Edition — Lifestyle Intervention chapter (Look AHEAD trial synthesis; Heymsfield SB & Wadden TA, NEJM 2017 data).