Do the effects of interventions aimed at the prevention of childhood obesity reduce inequities? A re-analysis of randomized trial data from two Cochrane reviews
Authors: Palmer Jennifer C , Davies Annabel L , Spiga Francesca , Heitmann Berit L , Jago Russell , Summerbell Carolyn D , Higgins Julian PT ,   Inequity in Obesity Prevention Trialists Collaborative Group
Published: June 2024

Background

Public health attempts to prevent obesity in children and young people should aim to minimize health inequalities. We aimed to assess whether there were differences in the effectiveness of the interventions included in two Cochrane reviews according to the eight PROGRESS inequity factors.

Methods

We collected data on change in BMI (standardized or unstandardized), subgrouped by baseline measures of PROGRESS factors, for intervention and control groups, from trial authors. We calculated the intervention effect per subgroup (mean difference), then contrasted these to estimate interactions between intervention and the baseline factors. We combined interaction estimates for each factor across trials using standard procedures for meta-analysis.

Findings

Our analysis of interventions from 81 trials found no substantial differences in effectiveness for different subgroups in most scenarios. However, in the younger age group (5-11 years), the effect of interventions on standardized BMI appeared to be higher in boys.

Interpretation

The Cochrane reviews found that interventions promoting physical activity (only) have a beneficial effect on BMI (compared with a control group) for children and young people aged 5-18 years, as well as interventions promoting physical activity alongside healthy eating for 5-11 year olds. Although these beneficial effects were small, when delivered at scale, they may have the potential to contribute meaningfully to reducing the prevalence of childhood obesity. Our findings suggest that those responsible for public health can promote these beneficial interventions without major concerns about increasing inequalities. Because many of the interventions studied, including school-based interventions, provide building blocks of ‘whole systems approaches’, the findings are relevant to policy and practice.

Funding

National Institute for Health and Care Research (NIHR).

Research in context

Evidence before this study

A core principle of any public health guidance is to minimize health inequalities. Two previous studies of the effects of interventions aiming to prevent obesity in children and young people, by promoting physical activity or a healthy diet, found that such interventions do not increase health inequalities. However, these studies used secondary data published in trial reports, limiting the data available for analysis. Two recent Cochrane systematic reviews and meta-analyses of over 200 randomized trials of interventions to prevent obesity in children and young people, found,on average, small beneficial effects of physical activity interventions in 5-18 year olds on (standardized and unstandardized) BMI and of combined physical activity and dietary interventions in 5-11 year olds. A previous modelling study found that small beneficial benefits such as these, when delivered at scale, have the potential to contribute meaningfully to reducing the prevalence of childhood obesity. However, average effects may mask differential effects on health equity. Our objective was to collect primary trial results (not previously reported) to examine whether effects of interventions vary according to factors related to inequity as represented by the PROGRESS acronym: place, race/ethnicity, occupation, gender/sex, religion, education, socio-economic status, and social capital.

Added value of this study

To the best of our knowledge, this is the first large-scale meta-analysis to assess the impact of interventions to prevent obesity in children and young people on health equity using primary data from randomized trials. Data from 81 trials were included, collected directly from the trialists as aggregate data by intervention and by subgroup, and combined in meta-analyses. We found no substantial impact of the interventions on inequalities, although in the younger age group (5-11 years), the effect of interventions (n=45) on standardized BMI was greater in boys.

Implications of all the available evidence

Those responsible for public health can be confident in promoting the types of interventions included in this meta-analysis to prevent obesity in children and young people (5-18 years), knowing they are unlikely to increase inequalities. One exception was that interventions for younger children may benefit from being equally engaging and enjoyable for females and males. We regard ‘whole systems approaches’ to comprise separate interventions (components) interconnected via a programme theory and logic model, including the types of interventions included in this meta-analysis. As such, our findings are relevant to those providing guidance on a whole systems approach to reducing the prevalence of obesity in children and young people alongside promoting health equity.