Body Mass Index

Topics: Obesity, Body mass index, Body shape Pages: 11 (3899 words) Published: May 12, 2010
International Journal of Obesity (2006) 30, 590–594 & 2006 Nature Publishing Group All rights reserved 0307-0565/06 $30.00

Body mass index in children and adolescents: considerations for population-based applications A Must1,2 and SE Anderson2
1 2

Department of Public Health and Family Medicine, Tufts University School of Medicine, Boston, MA, USA and The Friedman School of Nutrition Science and Policy, Tufts University, Boston, MA, USA

International Journal of Obesity (2006) 30, 590–594. doi:10.1038/sj.ijo.0803300 Keywords: review; body mass index; pediatrics; BMI z-score; overweight classification

After several years of experience with body mass index (BMI)for-age reference standards in the US, the UK, and elsewhere, reflection on ‘how things are going’ seems timely. In this issue, Reilly1 offers a summary of the evidence base for the diagnostic accuracy of BMI in youth and his perspective on what is achieved by a definition of overweight and obesity based on high BMI. To complement this, in our short review, we describe the BMI measure itself, the utility of a BMI z-score (s.d. score), their utility in cross-sectional and longitudinal applications in public health/surveillance, clinical and population-based research settings.

centiles,5 and the inaccuracy of assessing overweight by observation or ‘eye-balling’ has been established.6,7 Therefore, for screening or for epidemiologic research, using a weight/height index to define obesity has advantages that outweigh its limitations. Despite the likelihood of misclassification of the small percentage of individuals whose high BMI is due to lean muscle mass (e.g. some professional athletes), the great majority of individuals with high BMI have excess body fat.

Use of body mass index in children and adolescents Body mass index defined Body mass index is a measure of weight adjusted for height. It is calculated as weight in kilograms divided by the square of height in meters. Although BMI is an imperfect tool – it does not distinguish overweight due to excess fat mass from overweight due to excess lean mass – it is the most commonly used measure for assessing obesity in adults. Other methods of determining adiposity are more accurate,2 but have limited applicability to screening or studying large populations. The BMI is well correlated with these more direct fatness measures,3,4 and weight and height are simple, inexpensive, non-invasive measurements that are recorded routinely in clinical and research settings. Others have discussed the limitations of clinical screening for high adiposity by comparing weight centiles to height Correspondence: Dr A Must, Department of Public Health and Family Medicine, Tufts University, 136 Harrison Ave, Boston, MA 02111, USA. E-mail: Received 20 December 2005; revised 24 January 2006; accepted 5 February 2006

The BMI is used to assess weight status in children and adolescents as well as adults, but whereas in adults the BMI cut points that define obesity and overweight are not linked to age and do not differ for males and females, in growing children BMI varies with age and sex. Thus, a 5-year-old boy with a BMI of 20 kg/m2 is likely to be overfat, but a 15-yearold boy with a BMI of 20 kg/m2 is likely to be lean. As a result, for BMI to be meaningful in children it must be compared to a reference-standard that accounts for child age and sex.

Choice of a reference standard
National and international BMI-for-age reference standards are available. The US BMI-for-age reference is based on nationally representative data from boys and girls ages 2–20 years collected between 1963 and 1980.8 National reference standards are also in use in the UK,9 and are under development elsewhere. An international BMI reference has been produced by the International Obesity Task Force

BMI in children and adolescents A Must and SE Anderson

(IOTF) with data from...

References: 1 Reilly JJ. Diagnostic ability of the BMI for age in pediatrics. Int J Obes Relat Metab Disord 2006; 30: 595–597. 2 Sopher A, Shen W, Pietrobelli A. Pediatric body composition methods. In: Heymsfield SB, Lohman TG, Wang ZM, Going SB (eds.). Human Body Composition. Human Kinetics: Champaign, IL, 2005, pp 129–140. 3 Willett WC. Anthropometric measures and body composition. Nutritional Epidemiology, 2nd edn. Oxford University Press: New York, 1998, pp 244–272. 4 Pietrobelli A, Faith MS, Allison DB, Gallagher D, Chiumello G, Heymsfield SB. Body mass index as a measure of adiposity among children and adolescents: a validation study. J Pediatr 1998; 132: 204–210. 5 Cole TJ. A chart to link child centiles of body mass index, weight and height. Eur J Clin Nutr 2002; 56: 1194–1199. 6 Cross JH, Holden C, MacDonald A, Pearmain G, Stevens MC, Booth IW. Clinical examination compared with anthropometry in evaluating nutritional status. Arch Dis Childhood 1995; 72: 60–61. 7 CDC Nutrition and Physical Activity. CDC Growth Chart Training. June 22, 2005. Available at: nccdphp/dnpa/growthcharts/training/modules/index.htm Accessed December 10, 2005. 8 Kuczmarski RJ, Ogden CL, Grummer-Strawn LM, Flegal KM, Guo SS, Wei R et al. CDC Growth Charts: United States. National Center for Health Statistics: Hyattsville, Maryland, Dec 4, 2000. 9 Cole TJ, Freeman JV, Preece MA. Body mass index reference curves for the UK, 1990. Arch Dis Childhood 1995; 73: 25–29. 10 Cole TJ, Bellizzi MC, Flegal KM, Dietz WH. Establishing a standard definition for child overweight and obesity worldwide: international survey. BMJ 2000; 320: 1240–1243. 11 Janssen I, Katzmarzyk PT, Srinivasan SR, Chen W, Malina RM, Bouchard C et al. Utility of childhood BMI in the prediction of adulthood disease: a comparison of national and international references. Obes Res 2005; 13: 1106–1115. 12 Rona RJ, Chinn S. One cheer for the international definitions of overweight and obestiy. Arch Dis Childhood 2002; 87: 390–391. 13 Reilly JJ. Assessment of childhood obesity: national reference data or international approach? Obes Res 2002; 10: 838–840. 14 Deurenberg P. Universal cut-off BMI points for obesity are not appropriate. Br J Nutr 2001; 85: 135–136. 15 Centers for Disease Control and Prevention. CDC Growth Charts: United States. Available at: Accessed December, 2005.
International Journal of Obesity
BMI in children and adolescents A Must and SE Anderson
of black, white, and Hispanic children. Int J Obes Relat Metab Disord 2002; 26: S93. 36 Gustat J, Elkasabany A, Srinivasan S, Berenson GS. Relation of abdominal height to cardiovascular risk factors in young adults: The Bogalusa Heart Study. Am J Epidemiol 2000; 151: 885–891. 37 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: 482–488. 38 McCarthy HD, Ashwell M. A study of central fatness using waist-to-height ratios in UK children and adolescents over two decades supports the simple message – ‘keep your waist circumference to less than half your height. Int J Obesity Relat Metab Disord (advance online publication, 24 January 2006). 39 Wells JCK, Coward WA, Cole TJ, Davies PSW. The contribution of fat and fat-free tissue to body mass index in contemporary children and the reference child. Int J Obes Relat Metab Disord 2002; 26: 1323–1328.
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