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

Abstract

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 ( &#50 100%) 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.