There is currently no universally accepted system for the classification of childhood obesity. Across the world numerous Body Mass Index (BMI) classification systems are in operation, giving rise to a plethora of definitions arising from the diversity in sample size, nationality of reference populations, and use of different obesity cut points. For example, in the USA, the CDC 2000 centile charts (developed from a USA reference population) are used to establish overweight and obesity in individuals exceeding the 85th and 95th centile respectively. In the UK, the UK1990 reference charts (developed from a British reference population) are used to define overweight and obesity in individuals exceeding the 91st and 98th centiles when used within a clinical setting, and 85th and 95th centiles when used for population monitoring. The International Obesity Task Force (IOTF), on the other hand, have proposed an international definition based on data from six different countries, with cut points extrapolated from the adult BMI cut points of 25kg/m2 and 30kg/m2 for overweight and obesity at age 187,8. In addition, the World Health Organisation (WHO), have also released their new growth standards, in response to global surge in childhood obesity and the release of the new international growth standards for infants and preschool children.

Currently three BMI classification systems are available to the UK and are reviewed in Table 3.

Table 3: A Summary Comparison of the UK 1990, IOTF and WHO Definitions for Childhood Body Mass Index