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BMJ. 2006 Nov 18; 333(7577): 1031–1032.
PMCID: PMC1647355

Tackling childhood obesity

Requires a shift in social norms, not just an exercise programme

Despite heightened interest in preventing obesity in childhood, the evidence base for the effectiveness of local school based programmes and changes in policy to combat childhood obesity is poor.1 2 3 Even less research has been devoted to improving nutrition and physical activity in preschool and childcare settings, where further challenges exist, such as lack of uniformity between programmes and fragmented oversights by regulatory authorities.1 3 Yet increasing evidence shows that preschool practices can influence the overall energy expenditure of young children.4 w1

In this issue of the BMJ, Reilly and colleagues address this gap in the literature with a rigorously designed, cluster randomised controlled trial of an intervention to promote physical activity in 36 Scottish nursery schools.5 Body mass index and physical activity were not affected by the intervention at six and 12 months. These results contrast with recent studies showing that increasing children's physical activity can reduce weight gain,6 w2 and that changes in the quality and quantity of school based physical education can increase children's activity,7 w3 although it is not the only trial to find no benefit on body composition.8 w4

One weakness of the study is in the main outcome measure used. Body mass index does not correlate closely with changes in body composition (amount and distribution of body fat, bone mineral density, muscularity) in adults and school aged children. The association is probably even more tenuous in very young and rapidly growing children, especially as the authors used body mass index standard deviation scores, rather than the more widely used age and sex specific body mass index centiles.9 In addition, the authors acknowledge that the “dose” of physical activity they used may be too low to influence the overall amount or intensity of physical activity, the study's primary independent variable. And it is not clear whether the study was powered to disaggregate the data by sex and overweight status, which may reveal effects diluted across the full sample.

Ultimately, the success of interventions disseminated to a variety of settings hinges on effective implementation—selection and training of staff, organisational culture and support, continuing education, and technical assistance.10 The pilot study for Reilly and colleagues' trial did produce increases in physical activity.11 This may be because the intervention was delivered by head teachers in the pilot study, whereas it was delivered by nursery staff in the larger trial to increase generaliseability. In addition, it is not clear whether the socioeconomic status of the children in the pilot and main study were similar. If the children studied in the larger trial came from more affluent families than those in the pilot study, a ceiling effect might have prevented modest effects being apparent.

Despite these criticisms, we should not lose sight of the bigger picture. Reilly and colleagues' findings show once again that such interventions have only weak and transient positive effects on behaviour and ultimately weight. To promote activity in youth and redress childhood obesity, adults must act to influence children's daily environments, as decision makers, gatekeepers, opinion leaders, service providers, and role models. This will require widespread and comprehensive changes in social norms and values in nurseries, schools, and beyond.1 12 In today's fast paced society—where children aged 4-5 years are pushed in buggies rather than allowed to walk—temporary or circumscribed environmental changes are unlikely to have “permanent” effects.

However, preschool settings could be useful as part of a comprehensive strategy to prevent obesity. Preschool organisational practices and policies vary greatly4 w1 and may influence young children's fitness.7 13 While childcare settings may have less developed infrastructures than primary and secondary schools, they also have more flexible schedules and curriculums and tend to be less bureaucratic, which may help in adaptation and dissemination of interventions.4 Continuing investment and investigation are needed to identify approaches that work.

Supplementary Material

[extra: References]


Competing interests: None declared.

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Extra references w1-w4 are on bmj.com


1. Institute of Medicine (US). Progress in preventing childhood obesity: how do we measure up? Washington, DC: National Academies of Sciences, 2006.
2. Katz DL, O'Connell M, Yeh MC, Nawaz H, Njike V, Anderson LM, et al. Public health strategies for preventing and controlling overweight and obesity in school and worksite settings: a report on recommendations of the Task Force on Community Preventive Services. MMWR Recomm Rep 2005;54:1-12. [PubMed]
3. Story M, Kaphingst KM, French S. The role of child care settings in obesity prevention. Future Child 2006;16:143-68. [PubMed]
4. Dowda M, James F, Sallis JF, McKenzie TL, Rosengard P, Kohl HW 3rd. Evaluating the sustainability of SPARK physical education: a case study of translating research into practice. Res Q Exerc Sport 2005;76:11-9. [PubMed]
5. Reilly JJ, Kelly L, Montgomery C, Williamson A, Fisher A, McColl JH, et al. Physical activity to prevent obesity in young children: cluster randomised controlled trial. BMJ 2006. doi: 10.1136/bmj.38979.623773.55 [PMC free article] [PubMed]
6. LeMura LM, Maziekas MT. Factors that alter body fat, body mass, and fat-free mass in pediatric obesity. Med Sci Sports Exerc 2002;34:487-96. [PubMed]
7. Datar A, Sturm R. Physical education in elementary school and body mass index: evidence from the early childhood longitudinal study. Am J Public Health 2004;94:1501-6. [PMC free article] [PubMed]
8. Trost SG. School physical education in the post-report era: an analysis from public health. J Teaching Physical Educ 2004;23:216-35.
9. Centers for Disease Control and Prevention. National health and nutrition examination survey. CDC growth charts. www.cdc.gov/nchs/about/major/nhanes/growthcharts/datafiles.htm.
10. Yancey AK, Ory MG, Davis SM. Dissemination of physical activity promotion interventions in underserved populations. Am J Prev Med 2006;31(4S):82-91. [PubMed]
11. Reilly JJ, McDowell ZC. Physical activity interventions in the prevention and treatment of paediatric obesity: systematic review and critical appraisal. Proc Nutr Soc 2003;62:611-9. [PubMed]
12. Yancey AK, Fielding JE, Flores GR, Sallis JF, McCarthy WJ, Breslow L. Creating a public health infrastructure for physical activity promotion: a challenge to chronic disease control policy. Am J Prev Med (in press).
13. Fitzgibbon ML, Stolley MR, Schiffer L, van Horn L, Kaufer Christoffel K, Dyer A. Two-year follow-up results for Hip-Hop to Health Jr: a randomized controlled trial for overweight prevention in preschool minority children. J Pediatr 2005;146:618-25. [PubMed]

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