Defining overweight and obesity in pre-school children: IOTF reference or WHO standard?

Two international datasets are used to define overweight and obesity in pre-school children: the International Obesity Task Force (IOTF) reference and the WHO standard. This study compares the performance of the two datasets in defining overweight and obesity in 24-60 months old children. This was done by plotting the IOTF cut-offs against WHO curves and by comparing the prevalence of overweight and obesity, as defined by the IOTF reference and by the WHO standard, using 2001 data from the Czech Republic. The IOTF cut-off for overweight in 24-60 months old children goes from 1.7 to 1.1 z-scores on the WHO chart, and for obesity it shifts with age from 2.7 to 2.2 z-scores. As a consequence, at 5 years of age the prevalence of overweight in Czech girls is 3.4% using the WHO and 15.3% using the IOTF definition. These discrepancies are due to the choice of cut-offs and to the different criteria used to select the sample for the IOTF reference and the WHO standard. Research is urgently needed to identify, for the WHO standard, BMI cut-offs associated with an increased risk of overweight and obesity, and associated health outcomes later in life.