Adjustment of fat-free mass and fat mass for height in children aged 8 y

OBJECTIVE: To explore the relationships between height and (a) fat-free mass (FFM) and (b) fat mass (FM) in children in order to determine the optimum means of adjusting body composition for height. DESIGN: Cross-sectional study. SUBJECTS: Sixty-nine children aged 8 y. MEASUREMENTS AND METHODS: Weight and height (HT) were measured, and total body water by deuterium dilution for estimation of fat-free mass and fat mass. The indices FFM/HT(2) and FM/HT(2) were calculated, as were the indices FFM/HT(p) and FM/HT(p) where P was selected in order to eliminate the correlation of these indices with height. RESULTS: FFM was optimally adjusted for height by calculating FFM/HT(2). FM was optimally adjusted by calculating FM/HT(6). However, height accounted for <8% of the variation in FM/HT(2), indicating that the bias of this simpler index is small. CONCLUSIONS: Different adjustments of FFM and FM for height are possible, depending on the study design. The indices FFM/HT(2) and FM/HT(2) are appropriate for many purposes, and have the advantage of expressing both aspects of body composition in common units. However, in some scenarios a more sophisticated approach is required for evaluating body fatness.