PRELIMINARY EVIDENCE THAT DEXA PROVIDES AN ACCURATE ASSESSMENT OF BODY-COMPOSITION

It was previously found that dual-energy X-ray absorptiometry (DEXA) u nderestimated central body fat. The purposes of this study were to det ermine whether an updated version (enhanced version 5.64) of the analy sis program corrected this problem (experiment 1) and to compare body composition assessed by DEXA and hydrodensitometry (HD) in women (n = 225) and men (n = 110) across a 21- to 81-yr age range (experiment 2). For experiment 1, 10 subjects underwent DEXA procedures in a control condition and with packets of lard positioned over either the thighs o r the truncal region. DEXA accurately quantified the additional mass a s similar to 96% fat, regardless of position. For experiment 2, DEXA y ielded higher (P < 0.001) estimates of fatness than did HD (32.1 +/- 1 2.0 vs. 31.2 +/- 10.1%). The mean difference between the two methods w as similar in young, middle-aged, and older subjects, but was differen t in men (HD - DEXA, 1.6 +/- 3.4% of body wt) than in women (-2.1 +/- 3.8% of body wt). Correcting the density of fat-free mass for variance in the bone mineral fraction of fat-free mass reduced the difference between the methods in men from 1.6 +/- 3.4 to -0.7 +/- 2.9% but widen ed it in women from -2.1 +/- 3.8 to -3.5 +/- 3.4%. A second correction procedure that adjusted for variance in water, protein, and mineral f ractions of fat-free mass eliminated the differences in estimates of f at content by DEXA and HD in both men (21.1 +/- 9.3 vs. 20.6 +/- 8.4%, respectively) and women (37.5 +/- 9.3 vs. 36.8 +/- 8.0%, respectively ). These results provide encouraging, but not definitive, evidence tha t the assessment of body composition by DEXA is accurate under the spe cified conditions.