Mj. Hewitt et al., HYDRATION OF THE FAT-FREE BODY-MASS IN CHILDREN AND ADULTS - IMPLICATIONS FOR BODY-COMPOSITION ASSESSMENT, The American journal of physiology, 265(1), 1993, pp. 50000088-50000095
Previous studies have shown that children have a higher aqueous fracti
on of the fat-free body mass (FFM) than young adults. In older adults,
methodological differences among studies limit evaluation of potentia
l age-related differences in the water content of the FFM (W/FFM). The
refore, we determined W/FFM in 28 healthy white prepubescent children
(age = 5-10 yr), 31 young adults (age = 22-39 yr), and 62 older adults
(age = 65-84 yr), using (H2O)-H-2 dilution to estimate total body wat
er and a multicomponent approach based on body density, total body wat
er, and regional bone mineral density to estimate FFM. To quantify the
extent to which variation in W/FFM affects percent fat estimation err
or, differences in percent fat between our multicomponent approach and
the Siri two-component model were related to W/FFM. Prepubescent chil
dren (72.7 +/- 1.6%) and older adults (72.5 +/- 1.4%) were found to ha
ve significantly higher (P < 0.01) mean W/FFM than young adults (70.8
+/- 1.2%). Differences in percent fat between the multicomponent and t
wo-component models ranged from -10 to 6% fat and were significantly a
ssociated with W/FFM (r = -0.62, P < 0.0001). We conclude that prepube
scent children and older adults, on average, have a higher W/FFM than
young adults, and that, in adults, individual differences in W/FFM acc
ount for a substantial portion of the percent fat estimation errors as
sociated with the use of two-component body composition models.