DEXA SUPPORTS THE USE OF BMI AS A MEASURE OF FATNESS IN YOUNG GIRLS

OBJECTIVE: To examine the relationship of body fat mass measured by du al energy X-ray absorptiometry (DEXA) to BMI in young girls, according to age and normative BMI percentile groupings. DESIGN: Cross-sectiona l observation study. SETTING: Dunedin, an urban town in the South Isla nd of New Zealand. SUBJECTS: 196 healthy Caucasian girls aged 4-16 y. MEASUREMENTS: Body weight, height and BMI, total fat mass and % body f at (by DEXA). RESULTS: Our BMI percentile standard groupings were <5 c entile (n = 7); 5-50 centile (n = 71); 51-75 cenfile (n = 50); 76-90 c entile (n = 42); 91-95 centile (n = 12); >95 centile (n = 14). In this whole population sample DEXA-derived fat mass correlates well with BM I (n = 0.934) indicating that BMI accounts for 87.2% of the variance i n body fat mass. However, at the extremes of BMI the association is we aker. A nomogram for predicting DEXA fat mass from BMI in girls is pre sented. CONCLUSION: Because DEXA-derived fat mass correlates well with BMI throughout the 'normal' range of BMI (5-95th centiles) our study supports the usefulness of BMI as a simple measure of fatness in girls . Children with BMI values outside the normal BMI range may benefit fr om more exact body composition assessment using DEXA.