Body-composition assessment by dual-energy x-ray absorptiometry in subjects aged 4-26 y.

This cross-sectional study describes the body composition of 265 normal subjects (137 males and 128 females) aged 4-26 y determined by dual-energy x-ray absorptiometry (DXA). Lean tissue mass (LTM) and bone mineral content (BMC) increased with age in females until 13.4 and 15.7 y, respectively, and in males until 16.6 and 17.4 y, respectively. A strong relation between LTM and BMC was found for each sex (r = 0.98, P = 0.0001 for males; r = 0.98, P = 0.0001 for females). DXA percent body fat (%BFDXA) increased with age in females (r = 0.52, P < 0.001) but not in males and was higher in females than in males at all ages. Trunk to leg fat ratio (TLFR) was calculated as DXA trunk fat/leg fat. In post-pubertal age the TLFR was higher in males than in females (1.01 +/- 0.23 and 0.75 +/- 0.16, P = 0.001), but there was no sex difference in younger children. DXA weight underestimated scale weight by a mean of 0.83 kg. %BFDXA correlated with %BF by skinfold thickness measurement with good agreement for males but overestimated %BF by skinfold thickness for females. These normative data for body composition demonstrate significant sex differences in all body compartments after the pubertal years.