NIHR Signal Diet and physical activity interventions targeting children and youth have different, yet small, effects on preventing obesity
Published on 17 September 2019
Obesity prevention interventions which include both diet and physical activity may reduce the risk of obesity in pre-school children. Once at school, physical activity appears to be more effective for weight loss than diet alone. Resulting weight loss form any intervention, if any, has been very small with unclear benefits to the individual or population.
This NIHR-supported Cochrane systematic review pooled the results of 153 global randomised-control trials (seven from the UK) aiming to prevent childhood obesity. Most interventions targeted individual children at school and lasted less than a year. Other similar systematic reviews have found modest or no effect from childhood obesity prevention interventions targeting individual behaviour change.
As a result, Public Health England advocates a “whole system approach”. This targets the problem of expecting individual children to change their life-long habits without also addressing the powerful obesity-promoting environmental factors all around them.
- Child Health, Commissioning, Obesity and nutrition, Primary care, Physical therapy, Schools and colleges
Why was this study needed?
Obesity prevention is a public health priority in many countries across the globe, including middle‐ and low‐income countries. Once childhood obesity is established, it can be difficult to manage and often carries through into adulthood.
Obesity is a common problem affecting around 25% adults and 20% of children aged 10 to 11 in the UK. Treating obesity is also very expensive. In the UK in 2014, it was estimated that the NHS spent £5.1 billion on obesity-related illnesses.
Many research studies come out each year related to obesity prevention or treatment. This review aimed to determine the effectiveness of interventions that included diet or physical activity, or both, designed to prevent obesity in children. It updated an earlier 2011 review.
What did this study do?
This Cochrane systematic review looked for randomised control trials of obesity prevention in children and adolescents under 18 years.
A total of 153 trials were included (seven from the UK) and results were combined in a meta-analysis, where possible, to produce average estimates of effect.
Most trials targeted children aged 6 to 12 years and lasted 12 months or less. Most interventions were aimed at individuals, and took place in schools, the community, child‐care centres or preschools, and a minority at home or health centres.
All included studies were assessed for risk of bias, and the GRADE of the evidence by outcome ranged from very low to high. It was rated moderate for the main outcome (BMI). This means we can be reasonably confident in this result.
What did it find?
- Interventions that included diet and physical activity elements can reduce the risk of obesity in children aged 0‐5 years. But interventions that focused only on physical activity were not effective.
- By contrast, interventions that focused only on physical activity reduced the risk of obesity (BMI) in children aged 6 to 12 years, and adolescents aged 13 to 18 years. In these age groups, there was no evidence that interventions focussed only on diet were effective, and some evidence that diet combined with physical activity interventions may be effective.
- Despite statistically significant differences, the magnitude of change was generally very small.
- For example, for preschool children diet combined with physical activity reduced BMI by an average (mean difference [MD]) of 0.07 kg/m2 (95% confidence interval (CI) −0.14 to −0.01) compared with control, and had a similar effect on zBMI (MD −0.11, 95% CI −0.21 to 0.01). It isn’t clear whether these changes result in any health benefit at an individual or population level.
- A 2010 study on obese adolescents concluded that improvements in body composition and cardiometabolic risk could be seen with zBMI reductions of 0.25 or more, while greater benefits come from losing at least 0.5 zBMI. All the average changes reported in the review fell short of that threshold.
What does current guidance say on this issue?
The 2013 NICE Public Health Guideline (PH47) Weight management: lifestyle services for overweight or obese children and young people specifies the core components of lifestyle weight management programmes. It says to ensure all lifestyle weight management programmes for overweight and obese children and young people are multi-component. They should focus on:
- diet and healthy eating habits
- physical activity
- reducing the amount of time spent being sedentary
- strategies for changing the behaviour of the child or young person and all close family members.
Additional tools and resources are available to support the implementation of this guideline.
What are the implications?
The review implies that weight management interventions should contain diet and physical activity elements for those aged 0 to 5, but physical activity should be the main emphasis for young people aged 6 to 17.
This adds further detail to current NICE guidelines that recommend multi-component programmes for children and young people up to 17 years old, including both diet and physical activity.
The review authors state that other comprehensive reviews on this topic have found similar results, in that there is a modest effect or no effect of interventions that target individual change, to prevent obesity in children. This highlights the need for a system-wide approach that, for example, tackles the marketing of unhealthy food.
Expecting children to ignore the powerful environment triggers that promote obesity, may be asking too much.
Citation and Funding
Brown T, Moore T, Hooper L et al. Interventions for preventing obesity in children. Cochrane Database Syst Rev. 2019;(7):CD001871.
This study was funded by a number of sources including National Institute for Health Research (NIHR) Collaboration for Leadership in Applied Health Research and Care West (CLAHRC West), UK; and Fuse, NIHR Centre for Translational Research in Public Health, UK.
BMJ Best Practice. What is GRADE. London; British Medical Journal; 2019.
Ford AL, Hunt LP, Cooper A et al. What reduction in BMI SDS is required in obese adolescents to improve body composition and cardiometabolic health? Arch Dis Child. 2010;95:256–61.
NHS Health A-Z. Obesity. London: Department of Health and Social Care; updated 16 May 2019.
NHS website. What is the body mass index? London: Department of Health and Social Care; updated 15 July 2019.
PHE. Implementing the Whole Systems Approach to Obesity. London: Public Health England Blog; accessed 11 July 2018.
The search for robust approaches to prevent childhood obesity continues.
Despite an increase in the number of trials included in this review, the evidence is still scant. While individual-level interventions may show small impact they appear short-lived and of limited clinical significance.
Policymakers may take the view that some evidence is better than no evidence and continue to pursue diet and physical activity interventions, as part of a whole system approach, safe that they will not increase health inequalities. Others will take the view that population-level approaches including improved food formulation and creating active environments, may have larger impacts despite the lack of randomised trial evidence.
Rupert Suckling, Director of Public Health, Doncaster Council
The commentator declares no competing interests
Body mass index, or BMI, is a measure that uses your height and weight to work out if your weight is healthy.
The BMI calculation divides an adult's weight - measured kilograms - by their height - measured in metres squared. For most adults, an ideal BMI is in the 18.5 to 24.9 range.
For children and young people aged 2 to 18, the BMI calculation takes into account age and gender, as well as height and weight; this is called zBMI.