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22 May 2024
The highly cited Cochrane review ‘Interventions for preventing obesity in children’ has undergone a major update by researchers at NIHR ARC West, Fuse (the Centre for Translational Research in Public Health) at Durham University and the Universities of Bristol and Newcastle, Australia.
One of Cochrane’s most cited reviews and encompassing 153 studies at its last update in 2019, it has now been broken down into smaller age ranges. Cochrane has published the two reviews focusing on studies of interventions aimed at children aged 5-11 and 12-18.
The reviews show that a range of physical activity interventions, with or without a diet component, can have a modest beneficial effect on obesity in children and adolescents, without affecting health inequalities and without serious adverse events.
The ‘parent’ Cochrane review of interventions to prevent obesity in children focused on children aged 0-18. It has been updated five times since it was first published with seven studies in 2000.
Cochrane and the author team decided to divide it into four reviews for several reasons. Alongside the increased volume of studies, the need to consider children’s different developmental stages and the development of research methods and searching led to the change.
The review has been broken down by age. Today sees the publication of the primary school (5-11) and secondary school children and adolescents (12-18) reviews. The pre-school (2-4) review is due to be published later this year.
These reviews are the first to be published from these new groupings. The research team included 74 studies in the 12-18 age group review and 172 studies in the 5-11 one. Of these, 54 and 149 studies, respectively, contributed to the meta-analyses.
They looked at BMI, age- and sex-standardised BMI (zBMI) and percentile BMI, reported in randomised controlled trials with interventions aimed at changing diet, physical activity levels (including sedentary time) or both. The trials were delivered in any setting, with most being in schools.
In the younger age-group, they found that a range of school-based physical activity interventions, alone or in combination with diet interventions, may have a modest beneficial effect on obesity in childhood at short- and medium-term follow-up (between 3 and 15 months), but not at long term follow-up (15 months or more). Diet interventions alone may result in little to no difference.
In the older age group, they found at medium- and long-term follow-up (9 months or more) physical activity interventions may have a small beneficial effect on reducing BMI gain, whereas diet alone or diet plus physical activity interventions may result in little to no difference. They found no effect of interventions on zBMI. Certainty in evidence was low to very low.
They found no adverse effects of the interventions in either age group review and, although the information was limited, there is no evidence of increased inequalities.
The same team has been investigating, using more complex analytic syntheses, what specific characteristics of these interventions make them more effective in reducing BMI and make them more equitable. The findings will be published in research papers later this year.
The reviews are informing guidance on childhood obesity, with NICE including the analyses in their new guidance due to be published in Autumn 2024.
Dr Francesca Spiga, Senior Research Associate at the University of Bristol, is the lead first author of the updated reviews. She said:
“In terms of clinical relevance, it is important to point out that at a population level, even a very small benefit of an intervention that prevents the gain of excess weight, is meaningful.
“We know that the diet and activity habits adopted in childhood carry on throughout life. Therefore, there is the potential for a cumulative effect of small but sustainable changes towards a healthier diet and a more physically active lifestyle.
“A healthy diet and being physically active have many health and wellbeing benefits for children and adolescents beyond the promotion of a healthy body weight, including positive associations with academic achievement.”
Professor Carolyn Summerbell, Durham University and Deputy Director of Fuse, the Centre for Translational Research in Public Health, is the lead senior author of the updated reviews. She said:
“The number of new trials included in these reviews allows us to be more confident about the overall small but positive impact of this type of public health intervention to prevent obesity in school age children and adolescents. Indeed, I doubt more of the same school-based trials which target individual behaviour change would change these findings.
“But did these interventions increase health inequalities? Although many studies didn’t report on this, those that did suggest there was no impact. Those responsible for public health policy and implementing these types of interventions need this information.
“What we do know is that some children and adolescents who are most at risk of obesity don’t engage well with school (or school-based interventions) or are often excluded from trials. Knowing how these interventions work in community settings such as local youth clubs and faith-based groups, and in children and adolescents with disabilities, remains a gap in the evidence base.”
Luke Wolfenden, Co-ordinating Editor of Cochrane Public Health and Associate Professor at the University of Newcastle, Australia, is another author of the reviews. He said:
“Childhood and adolescence are a critical period for unhealthy weight gain. These reviews provide a comprehensive synthesis of evidence and useful guidance to support policy and practice decisions to improve child and adolescent health. They extend an earlier heavily cited review by this team.”
Professor Louise Baur, President of the World Obesity Federation and Chair of Child and Adolescent Health at the University of Sydney, said:
“It is very helpful to see this update of the Cochrane Review on the prevention of obesity. The evidence has grown in recent years and hence we now see, for the first time, specific reviews just for the 5-11 and 12-18 year age groups.
“The review team has undertaken a careful and detailed analysis of what are now many studies, especially in school settings. The review team rightly points out there is modest evidence of the effectiveness of school-based interventions on obesity in these age groups, with no evidence of adverse effects or any worsening of health inequalities.
“This information is very reassuring to policy-makers and practitioners alike. However, as noted by the review team, more evidence is needed in broader scale settings – outside of the school setting – and in a more diverse range of children and adolescents, especially those with disabilities.”
Read the reviews: