Analysing the studies behind Cochrane’s ‘Interventions for Preventing Obesity in Children’ review

What we did

We analysed the RCTs included in the 2019 Cochrane Review ‘Interventions for Preventing Obesity in Children’. Two researchers independently analysed which causes of obesity the studies aimed to address.

Because there are so many causes of obesity, we used a Public Health England tool to help this process. This tool groups the causes of obesity into one of five categories called the wider determinants of health:

• biological factors
• individual lifestyle factors
• social and community factors
• living and working conditions
• wider conditions

Two thirds of the causes of obesity are related to living and working conditions and wider conditions. We categorised the interventions tested in the 153 trials against these wider determinants of health.

What we found and what this means

Despite broad acknowledgement that obesity is caused by a wide range of factors, over 90 per cent of the trials had some focus on changing individual lifestyle factors, such as physical activity or diet. This was most often achieved through the delivery of educational sessions. There was also a strong emphasis on living and working conditions, although this mostly meant training teachers so that they could teach children about how to improve “lifestyle behaviours”.

Surprisingly we also found that the focus of these studies hadn’t changed much since 1993. They persisted in their focus on directly changing diet and physical activity, despite demonstrating very limited effectiveness. Interventions aimed at different age groups also had this same focus.

Our findings suggest that there is an imbalance between the causes of obesity and what trials to prevent childhood obesity focus on. This skewed focus has endured since the early 1990s and persists despite the growing recognition that population-level obesity is a complex systems issue.

What next?

Cochrane reviews and RCTs inform policymaking, and therefore influence how national and local governments seek to prevent childhood obesity. If the focus of these RCTs remains upon changing individuals diet and physical activity behaviours, then the policy that follows may have a persistent focus on individuals rather than the environments in which they live.

Our findings are particularly important for three groups:

1. Policymakers should be aware that the evidence base is skewed towards educational interventions that target individual diet and physical activity. It’s well known that obesity is a complex problem, so interventions need to address this complexity. Consider approaches that target the ‘upstream’ determinants of obesity such as living and working conditions rather than the ‘downstream’ determinants such as diet and physical activity.
2. Research funders should also be aware of this imbalance in the focus of RCTs. It is important to start considering other research designs which may be more appropriate for the evaluation of complex approaches to preventing childhood obesity. RCTs may not be the best approach.
3. Researchers need to develop new research approaches which account for the complexity of obesity when developing or evaluating interventions. This could include using alternative research designs to better understand how interventions can work upstream. Researchers should consider how interventions may help change the systems that encourage obesity, rather than solely focusing on whether they change the prevalence of obesity itself. Single interventions are also very unlikely to prevent childhood obesity.