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Childhood obesity, prevalence and prevention

Mahshid Dehghan, Noori Akhtar-Danesh* and Anwar T Merchant

Nutrition Journal 2005, 4:24  doi:10.1186/1475-2891-4-24

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Parents, not TV screens, should be targetted: A response to Dehghan, Akhtar-Danesh and Merchant

Owen Carter   (2006-03-26 04:22)  Centre for Behavioural Research in Cancer Contol, Curtin University of Technology email

Dehghan, Akhtar-Danesh and Merchant (2005) suggest that “numerous studies have shown that sedentary behaviors like watching television and playing computer games are associated with increased prevalence of obesity”. This statement is misleading, although it is true that data from North America, Europe and Oceania consistently indicate that childhood obesity and television viewing are related. Children watching above-average levels of television are approximately twice as likely to be obese (e.g., Wake, Hesketh & Waters, 2003; Janssen et al., 2005), however the correlational and cross-sectional nature of all such studies fails to suggest the direction of causation, so it might be equally true to say that obese children are twice as likely than their more svelte peers to undertake sedentary behaviours, such as watching television—which is equally plausible! Moreover, a meta-analysis of 52 studies by Marshall et al. (2004) suggested that time spent television viewing is able to explain only 0.5% of children’s body weight. Dehghan et al. also implicate playing video games but the same meta-analysis suggested there is virtually no relationship between time spent playing computer games and body weight at all. Interestingly the common presumption within the scientific literature is that children are more sedentary than previous generations due to increased television viewing behaviours (e.g., Eagle et al., 2004; Biddle et al., 2004; Bar-on, 2000). However, researchers have demonstrated that while access to television has increased in the past half a century, the amount of time that children spend watching television per capita has remained virtually unchanged throughout the intervening period, and furthermore time spent screen-viewing has merely displaced time formerly spent on other sedentary behaviours, such as going to the cinema, listening to music, reading comic books, playing board games, etc. (Carter, 2005; Marshall et al., 2004; Kaiser Family Foundation, 2004). As such interventions aimed at reducing childhood obesity by tackling television viewing and playing computer games are unlikely to have much affect at all. As highlighted by Dehghan et al., children’s energy consumption in developed countries has increased markedly in the past several decades—perhaps by around 15% in the last couple of decades. This alone is sufficient to explain increases in childhood obesity and explanations surrounding ‘decreases’ in physical activity levels are therefore superfluous. We merely need to recognise that increases in energy consumption have not been matched by increases in energy expenditure (i.e., physical activity).

Research suggests that a child with obese parents is ten-times more likely to be obese (Reilly et al., 2005). This raises the obvious scenario of an obese child’s environment where there is likely to be ready access to large quantities of energy-dense foods, provided by his or her parents, who also consume such. Given that obesity in adulthood is far higher than in childhood, perhaps the best way to tackle childhood obesity is to first tackle adult obesity. This need not be insurmountable: it has been estimated that for most of the population, a reduction of only 420KJ per day would be sufficient to stop weight gain in 90% of the population (Murray et al., 2005; Hill et al., 2003). This is the equivalent of walking an additional 2,000 steps, or drinking one cup less of soft drink or cordial. This should therefore be the concrete and easily understood message we promote to both children and adults, and especially parents, if we want to get serious about reducing the burgeoning epidemic of childhood obesity.

REFERENCES

Bar-on ME. (2000) The effects of television on child health: implications and recommendations. Arch Dis Child, 83(4):289-92.

Biddle S, Gorely T, Marshall S, I M, N C. Physical activity and sedentary behaviours in youth: issues and controversies. Journal of the Royal Society for the Promotion of Health, 124(1):29-33.

Eagle L, Bulmer S, de Bruin A, Kitchen PJ. (2004) Exploring the link between obesity and advertising in New Zealand. J Market Comm, 10:49-67.

Hill JO, Wyatt HR, Reed GW, Peters JC. (2003) Obesity and the environment: where do we go from here? Science 299(5608):853-5.

Kaiser Family Foundation (2004) The Role of Media in Childhood Obesity. Washington: The Henry J. Kaiser Family Foundation, 2004:12.

Marshall S, Biddle SJH, Gorely T, Cameron N, Murdey I. Relationships between media use, body fatness and physical activity in children and youth: a meta-analysis. International Journal of Obesity 2004;28(10):1238-1246.

Murray R, Frankowski B, Taras H. (2005) Are soft drinks a scapegoat for childhood obesity? J Pediatr 146(5):586-90.

Janssen I, Katzmarzyk PT, Boyce WF, Vereecken C, Mulvihill C, Roberts C, et al. (2005) Comparison of overweight and obesity prevalence in school-aged youth from 34 countries and their relationships with physical activity and dietary patterns. Obes Rev, 6(2):123–32.

Reilly JJ, Armstrong J, Dorosty AR, Emmett PM, Ness A, Rogers I, et al. (2005) Early life risk factors for obesity in childhood: cohort study. BMJ, 330(7504):1357.

Wake M, Hesketh K, & Waters E. (2003) Television, computer use and body mass index in Australian primary school children. J Paediatr Child Health, 39(2):130–4.

Competing interests

I declare that I have no competing interests.

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Consider pediatric use of the Waist-to-Height ratio

Henry Kahn   (2005-10-04 20:40)  National Center for Chronic Disease Prevention & Health Promotion, USA email

Your brief review of alternative definitions for pediatric obesity might also have considered the Waist-to-Height ratio (WHtR). This relatively simple index has been shown in at least 3 publications (citations below) to perform better than BMI or BMI percentiles for identification of children at risk of cardiometabolic disorders. Interestingly, this ratio may not require standardization for either sex or age of the children. Thus, its application in pediatric clinics could reduce the confusion that currently surrounds the interpretation of pediatric BMIs.

There are no publications that suggest what might be the cutpoints for defining an adverse WHtR value. The definition(s) of such cutpoints would depend, of course, on the their intended purpose. They might also vary depending on the population under examination.

References:

Savva SC, Tornaritis M, Savva ME et al. Waist circumference and waist-to-height ratio are better predictors of cardiovascular disease risk factors in children than body mass index. Int J Obes Relat Metab Disord. 2000;24(11):1453-1458.

Hara M, Saitou E, Iwata F, Okada T, Harada K. Waist-to-height ratio is the best predictor of cardiovascular disease risk factors in Japanese schoolchildren. J Atheroscler Thromb. 2002;9(3):127-132.

Kahn HS, Imperatore G, Cheng YJ. A population-based comparison of BMI percentiles and waist-to-height ratio for identifying cardiovascular risk in youth. J Pediatr. 2005;146(4):482-488.

Competing interests

None

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