Factors associated with effectiveness of interventions to prevent obesity in children: a synthesis of evidence from 204 randomized trials

Objective: To identify effective characteristics of behaviour change (physical activity and diet) interventions that prevent obesity in children aged 5 to 18 years. Design: A Bayesian multi-level meta-regression analysis of randomized trial results, with intervention and trial characteristics coded according to an analytic framework co-developed with stakeholders. Data source: Two Cochrane systematic reviews of the effects of interventions to prevent obesity in children, 5 to 11 years and 12 to 18 years, both updated in 2024. Main outcome measures: Mean difference (MD) in change from baseline in age- and sex- standardized BMI measured as a Z-score (zBMI). Results that had been reported as (unstandardized) BMI or BMI percentile were converted to zBMI using bespoke mapping techniques. Results: We included 204 trials (255 intervention arms) reporting data on at least one of the main outcome scales. Interventions were effective on average (MD in zBMI −0.037, 95% credible interval −0.053 to −0.022). The greatest effects were associated with medium term follow-up (9 to <15 months) and older children (12 to 18 years). We found evidence of small but beneficial effects for interventions targeting physical activity alone compared with diet alone (difference in MDs −0.227, −0.362 to −0.090) and small unfavorable effects for interventions that involved a change to the structural environment (the majority of changes were in the school food environment) (difference in MDs 0.05, 0.017 to 0.085). Accounting for interactions between covariates, we found that the most effective combination of intervention characteristics was to intervene in the school setting, with an individualized element to delivery, targeting physical activity, using multiple strategies of short duration and high intensity, and involving modification of behaviour through participation in activities. Conclusions: The most effective characteristic to include in a behaviour change intervention to prevent obesity in children aged 5-18 years was targeting of physical activity. This should not be interpreted as evidence that attempts to modify diet are not beneficial. Being physically active and consuming a healthy diet during childhood offer many important benefits beyond contributing to healthy weight and growth. Our findings suggest that interventions to prevent obesity in children should consider focusing primarily on the promotion of physical activity and consider other effective characteristics we identify here. ### Competing Interest Statement The authors have declared no competing interest. ### Clinical Protocols [https://research-information.bris.ac.uk/ws/portalfiles/portal/373709759/Analysis\_plan\_final.pdf][1] ### Funding Statement This work was funded by the National Institute for Health and Care Research (NIHR) Public Health Programme (grant number NIHR131572). FS, DMC, JS and JPTH were supported in part by the NIHR Bristol Evidence Synthesis Group. JPTH, JS and THMM were supported in part by the NIHR Applied Research Collaboration West (ARC West) at University Hospitals Bristol and Weston NHS Foundation Trust. ALD was supported in part by her Engineering and Physical Sciences Council (EPSRC) fellowship EP/Y007905/1. JPTH is a NIHR Senior Investigator (grant number NIHR203807). The views expressed in this paper are those of the authors and do not necessarily reflect those of the NIHR or Department of Health and Social Care. The funder had no role in the study design, analysis, interpretation, writing of the report or decision to submit the article for publication. All authors had full access to the data and can take responsibility for the integrity of the data and the accuracy of the data analysis. ### Author Declarations I confirm all relevant ethical guidelines have been followed, and any necessary IRB and/or ethics committee approvals have been obtained. Yes The details of the IRB/oversight body that provided approval or exemption for the research described are given below: studies identified and described in the Cochrane systematic reviews: https://www.cochranelibrary.com/cdsr/doi/10.1002/14651858.CD015328.pub2/full https://www.cochranelibrary.com/cdsr/doi/10.1002/14651858.CD015330.pub2/full I confirm that all necessary patient/participant consent has been obtained and the appropriate institutional forms have been archived, and that any patient/participant/sample identifiers included were not known to anyone (e.g., hospital staff, patients or participants themselves) outside the research group so cannot be used to identify individuals. Yes I understand that all clinical trials and any other prospective interventional studies must be registered with an ICMJE-approved registry, such as ClinicalTrials.gov. I confirm that any such study reported in the manuscript has been registered and the trial registration ID is provided (note: if posting a prospective study registered retrospectively, please provide a statement in the trial ID field explaining why the study was not registered in advance). Yes I have followed all appropriate research reporting guidelines, such as any relevant EQUATOR Network research reporting checklist(s) and other pertinent material, if applicable. Yes All data and codes that support the findings of this study are available at the GitHub repository: https://github.com/AnnieDavies/Obesity_Synthesis [1]: https://research-information.bris.ac.uk/ws/portalfiles/portal/373709759/Analysis_plan_final.pdf