The use of body mass index for measurement of fat mass in children is highly dependant on abdominal fat

We examined the relationship between body fat and body mass index (BMI) in a multiethnic population of obese children. BMI z-scores were compared to DEXA measures of whole body composition and regional fat distribution. Fat mass index (FMI) was best predicted by the equation: 1/[(0.159 – 0.013 × percentile of total abdominal fat) – (0.01 × BMI z-score)], where percentile of abdominal fat ranges from 1 to 5. Predicted FMI had high agreement with FMI measured by DEXA. There were no detectable differences in this relation between different ethnic groups. Both BMI and abdominal fat should be used as a proxy to determine adiposity.