Hydration of the fat-free body mass in children and adults: Implications for body composition assessment

M. J. Hewitt, S. B. Going, D. P. Williams, T. G. Lohman

Research output: Contribution to journalArticlepeer-review

89 Scopus citations


Previous studies have shown that children have a higher aqueous fraction of the fat-free body mass (FFM) than young adults. In older adults, methodological differences among studies limit evaluation of potential age- related differences in the water content of the FFM (W/FFM). Therefore, 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 2H2O dilution to estimate total body water and a multicomponent approach based on body density, total body water, and regional bone mineral density to estimate FFM. To quantify the extent to which variation in W/FFM affects percent fat estimation error, differences in percent fat between our multicomponent approach and the Siri two-component model were related to W/FFM. Prepubescent children (72.7 ± 1.6%) and older adults (72.5 ± 1.4%) were found to have significantly higher (P < 0.01) mean W/FFM than young adults (70.8 ± 1.2%). Differences in percent fat between the multicomponent and two-component models ranged from -10 to 6% fat and were significantly associated with W/FFM (r = -0.62, P < 0.0001). We conclude that prepubescent children and older adults, on average, have a higher W/FFM than young adults, and that, in adults, individual differences in W/FFM account for a substantial portion of the percent fat estimation errors associated with the use of two-component body composition models.

Original languageEnglish (US)
Pages (from-to)E88-E95
JournalAmerican Journal of Physiology - Endocrinology and Metabolism
Issue number1 28-1
StatePublished - 1993


  • body density
  • body water
  • multicomponent models

ASJC Scopus subject areas

  • Endocrinology, Diabetes and Metabolism
  • Physiology
  • Physiology (medical)


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