Abstract
PURPOSE The purpose of the study was to examine the effects of hydration status on body composition by Near Infrared Interactance (NIR), Bioelectrical Impedance Analysis (BIA), Air Displacement Plethysmography (ADP) and Dual Energy X-ray Absorptiometry (DEXA). METHODS Forty healthy college age males (n=20) and females (n=20) were assessed for percent body fat (%BF) by NIR, BIA, ADP and DEXA at initial visit, after euhydration and 1%, 2% and 3% dehydration. Mean differences among hydration conditions were assessed with a one between (Gender) by two within (Body Composition Methods, Hydration Status) repeated measures ANOVA. Selected orthogonal contrasts, and Post Hoc procedures with Bonferroni correction were employed to assess the influence of methods and hydration status on % BF. Significance levels were set at 0.05. RESULTS Euhydration did not significantly affect NIR and BIA assessment of %BF. However, euhydration significantly influenced ADP assessment of %BF among females. Dehydration did not significantly affect NIR assessment of %BF among females and only at extreme dehydration (> 2%) among males. Dehydration also did not significantly affect BIA assessment of %BF among males, but did significantly affect %BF among females. Dehydration significantly affected ADP assessment of %BF among both male and female subjects. Hydration status did not significantly influence DEXA assessment of %BF. At euhydration %BFDEXA was underestimated by NIR, BIA and ADP by 7%, 9% and 15%, respectively. Underestimation increased with dehydration levels for NIR (10%-13%), BIA (13%-17%) and ADP (22%-26%). Underestimation tended to be constant for NIR and BIA, but variable within subjects for ADP. CONCLUSIONS Accepting DEXA as the reference standard, it is concluded that NIR, BIA and ADP underestimate %BF in both genders and this underestimation increases during periods of dehydration. This study demonstrates that hydration status should be controlled when assessing %BF by NIR, BIA and ADP.
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