Key messages
- Strategies for changing activity levels, or both activity levels and diet, of children to help prevent them developing overweight or obesity might be effective in making small reductions in body mass index (BMI) in children aged 5 to 11 years.
- There is very little information about whether the strategies resulted in serious adverse events (e.g. injuries), but from what we found there appears to be little or no effect.
- This change in BMI, when provided to many children across a whole population, is useful for parents concerned about their children becoming overweight as they move into adulthood and for governments in trying to tackle the problems of obesity through the life course.
Why is preventing obesity in children important?
More children are developing overweight and obesity worldwide. Being overweight as a child can cause health problems, and people may be affected psychologically and in their social life. Children that are overweight are likely to be overweight as adults and continue to experience poor physical and mental health. Indeed, childhood obesity is associated with type 2 diabetes and heart disease in adulthood and middle-age mortality.
What did we want to find out?
We wanted to find out if strategies to help people modify their diet or activity (or both) are effective at preventing obesity in children aged 5 to 11 years. We also wanted to find out if these strategies were associated with any serious adverse events.
What did we do?
We searched many scientific databases to find studies that looked at ways of preventing obesity in children. We included studies aimed at children aged 5 to 11 years. We did not include studies only aimed at children who were already overweight or were already living with obesity. However, we included studies in which children who were overweight or living with obesity were included in the analysis. We only included studies if the methods they used were aimed at changing children's diet, or their level of activity (i.e. increasing physical activity or reducing inactive time), or both. We looked only for studies that randomly placed people into groups receiving different strategies (which may include changing nothing). We assessed the rigour of the studies to get a sense of how confident we were in their results. We grouped studies together for analysis depending on whether they aimed to improve diet, activity, or both.
What did we find?
We found 172 studies that involved 189,707 children. One hundred forty-six studies were based in high-income countries (e.g. the USA and in Europe). In 111 studies, the strategies were tried in schools, though 15 were based in the community, eight in the home and seven in clinical settings; one intervention was conducted by telehealth and 31 studies were conducted in more than one setting. Eighty-six strategies were implemented for less than nine months, with the shortest being conducted over one visit and the longest over four years. Non-industry funding was declared by 132 studies; 24 studies were funded in part or wholly by industry (e.g. food suppliers, pharmaceutical industry and private healthcare services).
Our statistical analyses included results from 149 studies of 160,267 children. We found that children who were helped with a strategy to change their activity levels alone or in combination with a strategy to change their diet may have their BMI reduced, compared with children who were not given any strategy. This means that these children may have been able to minimise their excess weight gain by a small amount which, for public health, is important. In contrast, children who were helped with a strategy to change their diet only did not have their BMI reduced.
Only a few studies reported any possible harms of the strategies, and no serious harms were identified in these.
What are the limitations of the evidence?
Our confidence in the evidence is moderate to very low. However, it is difficult to be confident that funding more studies, at least more school-based studies, would produce a much higher level of confidence in the results.
Four main factors reduced our confidence in the evidence.
1. Results were very inconsistent across the different studies.
2. A lot of the studies had limitations in how they were done.
3. There were not enough studies reporting particular types of outcomes for a particular duration of follow-up to be certain about the results for some comparisons, and also certain settings (e.g. community settings) were under-represented.
4. Results from some studies were not reported in a way such that we could include them in our analyses (e.g. without any detail of the difference between the strategies examined) and this may have an impact on the results of our analyses.
This review does not provide sufficient information to be able to assess how well strategies work for children with disabilities, or whether those implemented in community settings are effective.
How up-to-date is this evidence?
This review updates our previous review. The evidence is up-to-date to February 2023.
The body of evidence in this review demonstrates that a range of school-based 'activity' interventions, alone or in combination with dietary interventions, may have a modest beneficial effect on obesity in childhood at short- and medium-term, but not at long-term follow-up. Dietary interventions alone may result in little to no difference. Limited evidence of low quality was identified on the effect of dietary and/or activity interventions on severe adverse events and health inequalities; exploratory analyses of these data suggest no meaningful impact. We identified a dearth of evidence for home and community-based settings (e.g. delivered through local youth groups), for children living with disabilities and indicators of health inequities.
Prevention of obesity in children is an international public health priority given the prevalence of the condition (and its significant impact on health, development and well-being). Interventions that aim to prevent obesity involve behavioural change strategies that promote healthy eating or 'activity' levels (physical activity, sedentary behaviour and/or sleep) or both, and work by reducing energy intake and/or increasing energy expenditure, respectively. There is uncertainty over which approaches are more effective and numerous new studies have been published over the last five years, since the previous version of this Cochrane review.
To assess the effects of interventions that aim to prevent obesity in children by modifying dietary intake or ‘activity’ levels, or a combination of both, on changes in BMI, zBMI score and serious adverse events.
We used standard, extensive Cochrane search methods. The latest search date was February 2023.
Randomised controlled trials in children (mean age 5 years and above but less than 12 years), comparing diet or 'activity' interventions (or both) to prevent obesity with no intervention, usual care, or with another eligible intervention, in any setting. Studies had to measure outcomes at a minimum of 12 weeks post baseline. We excluded interventions designed primarily to improve sporting performance.
We used standard Cochrane methods. Our outcomes were body mass index (BMI), zBMI score and serious adverse events, assessed at short- (12 weeks to < 9 months from baseline), medium- (9 months to < 15 months) and long-term (≥ 15 months) follow-up. We used GRADE to assess the certainty of the evidence for each outcome.
This review includes 172 studies (189,707 participants); 149 studies (160,267 participants) were included in meta-analyses. One hundred forty-six studies were based in high-income countries. The main setting for intervention delivery was schools (111 studies), followed by the community (15 studies), the home (eight studies) and a clinical setting (seven studies); one intervention was conducted by telehealth and 31 studies were conducted in more than one setting. Eighty-six interventions were implemented for less than nine months; the shortest was conducted over one visit and the longest over four years. Non-industry funding was declared by 132 studies; 24 studies were funded in part or wholly by industry.
Dietary interventions versus control
Dietary interventions, compared with control, may have little to no effect on BMI at short-term follow-up (mean difference (MD) 0, 95% confidence interval (CI) -0.10 to 0.10; 5 studies, 2107 participants; low-certainty evidence) and at medium-term follow-up (MD -0.01, 95% CI -0.15 to 0.12; 9 studies, 6815 participants; low-certainty evidence) or zBMI at long-term follow-up (MD -0.05, 95% CI -0.10 to 0.01; 7 studies, 5285 participants; low-certainty evidence). Dietary interventions, compared with control, probably have little to no effect on BMI at long-term follow-up (MD -0.17, 95% CI -0.48 to 0.13; 2 studies, 945 participants; moderate-certainty evidence) and zBMI at short- or medium-term follow-up (MD -0.06, 95% CI -0.13 to 0.01; 8 studies, 3695 participants; MD -0.04, 95% CI -0.10 to 0.02; 9 studies, 7048 participants; moderate-certainty evidence).
Five studies (1913 participants; very low-certainty evidence) reported data on serious adverse events: one reported serious adverse events (e.g. allergy, behavioural problems and abdominal discomfort) that may have occurred as a result of the intervention; four reported no effect.
Activity interventions versus control
Activity interventions, compared with control, may have little to no effect on BMI and zBMI at short-term or long-term follow-up (BMI short-term: MD -0.02, 95% CI -0.17 to 0.13; 14 studies, 4069 participants; zBMI short-term: MD -0.02, 95% CI -0.07 to 0.02; 6 studies, 3580 participants; low-certainty evidence; BMI long-term: MD -0.07, 95% CI -0.24 to 0.10; 8 studies, 8302 participants; zBMI long-term: MD -0.02, 95% CI -0.09 to 0.04; 6 studies, 6940 participants; low-certainty evidence). Activity interventions likely result in a slight reduction of BMI and zBMI at medium-term follow-up (BMI: MD -0.11, 95% CI -0.18 to -0.05; 16 studies, 21,286 participants; zBMI: MD -0.05, 95% CI -0.09 to -0.02; 13 studies, 20,600 participants; moderate-certainty evidence).
Eleven studies (21,278 participants; low-certainty evidence) reported data on serious adverse events; one study reported two minor ankle sprains and one study reported the incident rate of adverse events (e.g. musculoskeletal injuries) that may have occurred as a result of the intervention; nine studies reported no effect.
Dietary and activity interventions versus control
Dietary and activity interventions, compared with control, may result in a slight reduction in BMI and zBMI at short-term follow-up (BMI: MD -0.11, 95% CI -0.21 to -0.01; 27 studies, 16,066 participants; zBMI: MD -0.03, 95% CI -0.06 to 0.00; 26 studies, 12,784 participants; low-certainty evidence) and likely result in a reduction of BMI and zBMI at medium-term follow-up (BMI: MD -0.11, 95% CI -0.21 to 0.00; 21 studies, 17,547 participants; zBMI: MD -0.05, 95% CI -0.07 to -0.02; 24 studies, 20,998 participants; moderate-certainty evidence). Dietary and activity interventions compared with control may result in little to no difference in BMI and zBMI at long-term follow-up (BMI: MD 0.03, 95% CI -0.11 to 0.16; 16 studies, 22,098 participants; zBMI: MD -0.02, 95% CI -0.06 to 0.01; 22 studies, 23,594 participants; low-certainty evidence).
Nineteen studies (27,882 participants; low-certainty evidence) reported data on serious adverse events: four studies reported occurrence of serious adverse events (e.g. injuries, low levels of extreme dieting behaviour); 15 studies reported no effect.
Heterogeneity was apparent in the results for all outcomes at the three follow-up times, which could not be explained by the main setting of the interventions (school, home, school and home, other), country income status (high-income versus non-high-income), participants' socioeconomic status (low versus mixed) and duration of the intervention. Most studies excluded children with a mental or physical disability.