Thesis (M.Sc.)--Chulalongkorn University, 1999

This study examined the validity of bioelectrical impedance analysis (BIA) for estimating fat mass (FM) and percent body fat (%BF). Thirty-three healthy Thai people (19 males and 14 females) ranging in age from 19 to 41 yr participated in this study. The reference method was underwater weighing (UW) at residual lung volume. Body density was converted to percent body fat using Siri equation. %BFHW used to calculated reference fat mass. FMBIA and %BFBIA were measured using a Bodystat 1500 bioelectrical impedance analyzer. The cross-validation statistical analysis included examination of the constant error (CE), standard error of estimate (SEE), r, and total error (TE). There were significant correlations of FM and %BF between HW and BIA (0.56-0.77 and 0.61-0.85, respectively; p<0.05). The BIA resulted in high CE values, indicating that BIA estimates significantly underestimated both FM and %BF (3.48-4.22 and 6.71-6.91, respectively; p<0.005). In addition, the prediction errors (SEE and TE) estimated by BIA were also high values (SEE = 2.07-3.31 of FM, SEE = 3.84-5.23 of %BF, TE = 4.02-5.32 of FM, and TE = 7.68-8.63 of %BF). For individual, the %BFBIA within +_ 4% BF was 30% of the subjects. In conclusion, BIA technique does not accurately estimate body composition in healthy Thai populations when BIA manufacturer's equation are used.