Validity of bioelectric impedance equations used in estimation of fat free mass in young men and women

The aim of this study was to determine the validity of selected equations that predict fat free mass (FFM) from Bioelectric Impedance Analysis (BIA) values measured by two different methods in young men and women with reference method Dual Energy X-ray Absorptiometry (DXA). A total of 195 young adult individuals, 113 males and 82 females between 18 and 25 years, participated in the study voluntarily. Body composition parameters measured by foot-to-foot (FF) BIA, hand-to-foot (HF) BIA and selected reference method DXA. The FFM of the participants were determined by commonly used 8 equations which were developed for single frequency (50 kHz) BIA devices by using resistance, reactance and impedance values obtained from two different BIA. Differences between FFM and Body Fat Percentage (%BF) values obtained from BIA equations and reference method (DXA) were analyzed by paired samples t-test. The correlation coefficient and standard error of the estimation were determined by regression modeling from FFM and %BF values obtained from each BIA equation and DXA. Bland-Altman 95% consistency limits were determined for FFM and %BF which was obtained from the BIA equations and DXA. Results indicated that, Lukaski equation were found to be valid for FFM and Kyle01 and Lukaski equations are valid for %BF estimation in men; however, Deurenberg90, Deurenberg91 and Sun equations were found to be valid for FFM and Deurenberg90 equation was valid for %BF in women. The Kyle03 equation had the highest error and difference average in both genders. When the equations using the impedance value obtained from the different BIA methods compared with the reference method, the FF BIA method had higher standard error and mean difference. The findings of this study demonstrated that the BIA equations used for body composition assessment are population specific.