Mike: Hello, I'm Mike Clarke, podcast editor for the Cochrane Library. Since 2002, Cochrane has maintained a series of reviews on interventions to prevent obesity in children and young people. The sixth update, focusing separately on those aged 5 to 11 and 12 to 18 years of age, was published in April 2024. We asked one of the authors, Francesca Spiga from Bristol Medical School in the UK to tell us about the importance of the reviews and the latest findings and she prepared this podcast, which was recorded using ElevenLabs.

Francesca: Worldwide, more and more children and adolescents are developing overweight and obesity, which can cause serious health problems including diabetes. The person’s well-being and social networks may also be negatively impacted. Furthermore, puberty, and moving into adulthood, are a challenging time for some children. Many struggle with their mental health regardless of their body size and shape, but children and adolescents living with overweight and obesity are likely to suffer more. They are also likely to be overweight or obese when they become adults. This means that they may continue to experience poor physical and mental health, with obesity being a risk factor for many diseases in adulthood, such as diabetes, cardiovascular illness, several type of cancers, and mental health disorders including depression.
The reviews allow us to investigate if interventions to help children and young people modify their diet or activity, by which we mean physical activity, exercise and sedentary behaviour, prevent obesity. We searched widely for studies and looked at their results for body mass index, or BMI, which is a measure of adiposity, or fatness, based on weight and height. Children, as they grow, become taller and gain weight, but if they gain too much weight, their BMI will be higher than what is considered to be a healthy value.
We looked for studies that randomly allocated children or adolescents to an intervention or a control group and we grouped similar studies together for analysis. We also assessed the rigour of the studies, to get a sense of how confident we should be in the results.
We found 172 studies that involved almost 190,000 children and 74 studies with more than 80,000 young people. Most of the studies were done in high-income countries, and most of the interventions were tested in schools, with only a few based in the home or other places, such as the community, for example youth groups, or in clinical settings, such as general practice.
Turning to the results, children who received an intervention to change their activity levels alone or together with an intervention to change their diet, showed a small reduction in BMI gain compared to those not given any intervention.  In contrast, those who only received an intervention to change their diet did not gain less BMI than those in the control group.
Adolescents who received an intervention to change their diet and activity levels together did not gain less BMI than those in the control group. However, those who received an intervention that focused only on improving their activity levels showed a small reduction in BMI gain compared to adolescents who were not given any intervention. There were similar findings for adolescents who received an intervention that focused only on improving their diet, but the results in this group are very uncertain. The benefits were mainly observed for interventions that lasted, on average, at least a year. Importantly, we did not find strong evidence that the interventions caused serious harms, such as injuries or eating disorders.
However, overall, our confidence in the evidence is low. The results were very inconsistent across the different studies. Many studies had limitations in how they were done, such as the randomisation of the participants or the analysis methods, and results from some studies were not reported in a way that allowed us to include them in our analyses. Furthermore, some settings, such as home or the community, were underrepresented.
Looking to the future, more studies are needed in non-school settings including the wider community and in non-high-income countries, as well as more upstream interventions such as policy initiatives tackling the marketing of unhealthy foods or drinks. Researchers should also do more to include children and young people with physical and mental disabilities.
In summary, this research and our reviews remain important because, at a population level, even a very small benefit from an intervention that prevents the gain of excess weight, is meaningful and diet and activity habits adopted in childhood carry-on throughout life. There is also the potential for a cumulative effect of small but sustainable changes towards a healthier diet and a more physically active lifestyle, with a good diet and physical activity bringing health and wellbeing benefits beyond the promotion of a healthy body weight, including better academic achievement.

Mike: To read more about this, and the evidence for the effects of the interventions that have been tested in children and adolescents aged between 5 and 18 years of age, the two reviews are available at Cochrane Library dot com. If you go to the website and search ‘preventing obesity in children and adolescents’, you’ll see the links to them.