The following is adapted from Obesity Research Information Centre (oric) provided by the ASSOCIATION FOR THE STUDY OF OBESITY : For full document please see www.aso.org.uk
Height, weight and body mass index
Childhood obesity has usually been categorised using measures such as weight for height and weight for age. Recently, attention has focused on the use of the body mass index (BMI)(kg/m2). Age-related body mass index centile charts are available based on population norms. Overweight and obesity are usually defined as the 85th and 95th percentiles for the child’s age.
However, researchers have been dissatisfied with a reliance on these charts charts for two reasons:
To help overcome these problems, a new system has been devised which is based on many thousands of children from six large nationally representative cross-sectional growth studies (
Cole, Bellizzi et al. 2000). Gender-specific body mass index cut off points at 0.5 year intervals, from 2 to 18 years, are used to classify overweight and obesity. These values have been projected backwards from adult BMI values for overweight (25+) and obesity (30+) that are known to be associated with increased levels of ill-health. The greatest immediate value of this new system is to researchers who need to compare obesity levels in different countries using the same criteria.
Practising health professionals have a choice. They can either use centile charts, such as those issued in UK by the
Child Growth Foundation, or they can use the International values which are superimposed on the latest version of these charts.
Waist circumference
In adults, the waist circumference is a simple proxy for the amount of internal fat which is known to relate more to health risks than the amount of total fat which is assessed by measuring BMI. Centile charts of waist circumference have recently been produced for children of different ages. A high waist circumference centile added to a high BMI centile will confirm fatness linked to health risks more conclusively. However, waist circumference cannot yet be recommended as a means of diagnosing childhood obesity, as at present there is no evidence on the screening ability of any proposed cut-offs in children.
In adults, a simple rule of thumb to avoid the health risks of obesity is to keep your waist circumference to less than half your height. From very preliminary evidence, it looks as though this simple, rough, rule might work for children of all ages too.
Reference
Cole, T., M. Bellizzi, et al. (2000). "Establishing a standard definition for child overweight and obesity worldwide: international survey."
BMJ 320: 1240-1243.
