Classification of body composition in 11–14 year olds by both body mass index and bioelectrical impedance

This study investigated the prevalence of obesity in 1671 Caucasian 11–14 year olds using body mass index (BMI) and fat percentage (F%). Age and sex‐related criteria for both BMI and F% were applied to characterise the individuals as normal, overweight/overfat or obese. Using BMI, 5.6% males and 6.1% females were identified as obese. F% gave higher values for obesity: 11.9% males and 15.3% females. The prevalence of obesity appears to be in‐line with other surveys; however, the outcome does appear to depend on both the measure employed (BMI/F%) and the categories used (overweight/obese). Questions are raised by this survey as to whether BMI is underestimating the number of individuals who are obese, given that obesity is a factor of adiposity, and whether the two measures are identifying the same individuals as obese; 23% were categorised differently between the two measures. These issues have implications for both survey and clinical work.