Age-related differences in body composition by hydrodensitometry and dual- energy X-ray absorptiometry

D. B. Snead, S. J. Birge, W. M. Kohrt

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To determine whether percent body fat (%BF) is overestimated in older people by hydrodensitometry (HD) because of an age-related decrease in bone mineral content (BMC), body composition of 113 women and 72 men (21-81 yr) was assessed by HD and dual-energy X-ray absorptiometry (DEXA). DEXA provides an estimate of %BF adjusted for differences in BMC. HD %BF and DEXA %BF were not different in young people [21-39 yr; 17.6 ± 6.4 (SD) vs. 17.6 ± 7.2%, NS], were slightly, but significantly, different in middle-aged people (40- 59 yr; 25.5 ± 6.4 vs. 24.1 ± 6.7%, P < 0.05), and showed the largest disparity in older people (≥60 yr; 34.9 ± 7.9 vs. 30.8 ± 8.7%, P < 0.05). The discrepancy in older people was apparently not due to mineral loss, however, inasmuch as correction of HD %BF for variance in BMC as a fraction of fat-free mass resulted in only small adjustments (~1%) of %BF. Assessment of DEXA %BF was further evaluated in nine subjects with packets of lard (2-3 kg) overlying either the thigh or the trunk region. Only 55% of the exogenous fat was identified as fat when it was in the trunk region compared with 96% when it was positioned over the legs. These data suggest that the age- related increase in upper body adipose tissue is underestimated by DEXA.

Original languageEnglish
Pages (from-to)770-775
Number of pages6
JournalJournal of Applied Physiology
Issue number2
StatePublished - 1993


  • adiposity
  • body density
  • body fat
  • bone density
  • bone mineral
  • fat mass
  • fat- free mass


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