Globally, 80m adolescents are living with obesity, and without a substantial intervention the figure is due to rise to 150m by 2030. But what interventions work?

The latest ‘review of reviews’ on effective interventions for adolescent obesity prevention, by Flodgren et al, has found a disappointing lack of convincing evidence. Published (open-access) by Obesity Reviews in July, the review is one of the outputs of the EU-funded CO-CREATE project.

The researchers found 13 systematic reviews of interventions aimed at preventing overweight and obesity in adolescents which were suitable for inclusion, although only one was of high quality according to the AMSTAR 2 instrument. Three reviews focused on dietary behaviour, six on physical activity, and four on both. The evidence was dominated by individual-oriented and school-based interventions.

Results across reviews showed little or no effect on body mass index (BMI), or physical activity levels of adolescents, and only slight effects on dietary behaviour such as reducing consumption of sugar-sweetened beverages.

Weak evidence

The authors conclude that there is a lack of convincing evidence for interventions to improve health behaviour or to prevent overweight in adolescents. The findings echo those of the 2019 Cochrane review of childhood obesity prevention programmes: it found that interventions were largely school-based, that no interventions were effective in older children, and that even in younger children (under 12 years) interventions achieved a reduction of less than 1% of BMI compared with controls.

In part, the weakness of evidence may be linked to the limited settings for interventions. Most occur in schools, mainly because this provides the nearest available model for the ‘gold standard’ of evidence, a randomised controlled trial (RCT). Although they may not be ideally matched, schools can be randomly allocated to ‘intervention’ or ‘control’ and the results compared. Furthermore, schools have been identified as a crucial environment to implement obesity prevention and mitigation interventions, given their ability to reach almost 100% of children, independently of ethnic or socio-economic status. However, this approach severely limits the sort of intervention that can be designed, towards those which aim to get individual children to change their behaviour, rather than interventions which make sustainable changes in the wider environments that shape children’s health.

In spite of these limitations, it is frustrating that researchers and their funding agencies still pursue school interventions: the number of published papers found in PubMed (searching for ‘school’ and ‘obesity’) now tops 116,000, with nearly 13,000 published in 2019 alone, up from 4,000 in 2009. 

So, what should be done instead?

Re-positioning prevention

Despite the persistent view that adolescents’ health behaviour can be changed by educational means, the evidence does not support this. The assumption that providing an adolescent with information is sufficient to improve their health is contradicted by the known risk factors for adolescent obesity. These factors are largely outside an adolescent’s control, and the root causes of obesity include family socio-economic and ethnic status, earlier childhood, infant and placental nutrition, exposure to endocrine disrupting chemicals, cost and availability of food and exposure to unhealthy food promotions,  as well as genetic propensity to gain weight.

Policies to influence these risk factors are far beyond the reach of school interventions, and require a disruptive shift in the prevailing organisation of systems, including food supply, petrochemical, urban design and transport systems. There is plenty of scope for overlapping double- or triple-duty actions which can tackle global heating and poverty while also addressing food supplies and transport, as has been outlined in the Lancet Global Syndemic report. This is an agenda the research community needs to consider, using policy-supporting evidence beyond the RCT model to include time-series analyses of population interventions, modelling, and other analytical techniques, and extending the focus from effectiveness to include acceptability, sustainability, cost and equity impacts of policies (see our blog here).

Developing new policies across such a wide front is challenging but not impossible. It requires, among other things, public demand for change and a government sense of urgency. It requires tailoring programmes to the targeted audiences to ensure that developed policies are feasible both in terms of socio-cultural acceptability and available resources. We have seen demands from young people for action on environmental contamination and global heating, and for racial equity. We have seen the ability of governments to act to protect human health when faced with infectious disease.

By highlighting to young people the connections between the issues they care about – their health and wellbeing and their environment and social equality – we can help unlock greater demand for systemic policy change to improve health.  If we are to use schools as a point of intervention, then we should add to the curriculum courses on political activism and health advocacy.