The use of body mass index to predict body composition in children

BACKGROUND: Simple anthropometric indices of body composition have particular appeal for use in children, and as such body mass index (BMI) has been used to predict percentage body fat in a number of studies. AIM: To evaluate the relationship between BMI and percentage body fat (%body fat) and a proposed, more appropriate relationship between BMI and fat mass/height(2) in a cohort of young children. SUBJECTS AND METHODS: Cross-sectional study of 109 children aged between 6 and 10 years residing in either Sydney or Brisbane, Australia. Weight and height were measured using standard methods. Body composition was measured using a stable isotope method to firstly determine total body water and subsequently fat free mass. RESULTS: The correlation between BMI and fat mass/height(2) was markedly greater than that between BMI and percentage body fat. In the entire group of children the R(2) (x100%) value for the relationship between BMI and fat mass/height(2) was 73.3% compared with 46.5% for the relationship between BMI and percentage body fat. CONCLUSIONS: We have shown that the use of BMI to predict fat mass/height(2), and consequently percentage body fat, is superior to the use of BMI to predict percentage body fat based directly upon the R(2) values of the above analysis.