Body mass index and percentage fat mass in healthy German schoolchildren and adolescents

Abstract

OBJECTIVE: To provide reference data for obesity indices in Mid-European schoolchildren and adolescents, to evaluate the usefulness of body mass index (BMI) as an indicator of obesity in children, and to analyse the patterns of fat accumulation during childhood.

DESIGN: Cross-sectional observational study in 2554 healthy schoolchildren and adolescents (age, 6–19 y) living in Heidelberg, Germany in 1989/1990. Centile charts for BMI and skinfold-derived percentage body fat mass (PFM) were constructed using Cole’s LMS method for normalised growth standards.

RESULTS: The BMI centile values of German children ranged higher than French, lower than North American and Italian, and similar to Swedish and British children. While BMI steadily increased with age, PFM was markedly lower in peripubertal than in pre- and postpubertal boys. BMI predicted PFM with reasonable precision in girls (r=0.84), and in obese boys (r=0.58), but not in the leaner two thirds of the male population (r=0.01, NS). The 75th BMI percentile was the most appropriate cutoff value to screen for the 15% most obese patients by PFM (sensitivity: 82%, specificity: 85%). The pattern of the trunk-to-extremity skinfold ratio across childhood suggested that the typical adult distribution of central and peripheral fat is achieved in mid puberty in girls, but not before the end of adolescence in boys.

CONCLUSIONS: The major differences observed between BMI charts obtained in different countries underline the need for population-specific reference data. BMI is of limited usefulness in predicting relative fat mass in individual children. The developmental pattern of fat accumulation and distribution during adolescence is highly dynamic and gender-specific.