The Measurement and Epidemiology of Child Obesity

This chapter focuses on the classification of high levels of BMI and body fatness, the relation of BMI to body fatness among children, and the ability of a high BMI to identify children with excess body fatness. Many of the results are based on published data from the Pediatric Rosetta Study, but several are from unpublished analyses of this large data set. Based on levels of BMI, there have been marked increases in child obesity over the past few decades in most countries that have recent, representative data. BMI, however, is a measure of weight relative to height, and several investigators have concluded that a large proportion of children with excess body fatness do not have a high BMI (low sensitivity). However, after accounting for race and age differences, BMI levels among children are a fairly good predictor of body fatness in linear regression models, with BMI accounting for about 77% (boys) to 79% (girls) of the variability in percentage body fat.