Cross‐Validation of Fat‐Free Mass Estimated From Body Density Against Bioelectrical Resistance: Effects of Obesity and Gender

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Abstract
GORAN, MICHAEL I AND M ABU KHALED. Cross‐validation of fat‐free mass estimated from body density against bioelectrical resistance: effects of obesity and gender. Obes Res. The major purpose of this study was to examine whether estimates of body composition from bioelectrical resistance were systematically biased by obesity and/or gender (using hydrodensitometry as a comparison method). We compared fat‐free mass (FFM) by bioelectrical resistance (BR) using 5 equations (Lukaski, Kushner, Rising, Khaled, and Segal) to FFM by hydrodensitometry (HD) in 20 lean men, 30 lean women, 33 obese men and 22 obese women. None of the BR equations was successfully cross‐validated against FFM by HD in all 4 sub‐groups. The Lukaski equation significantly underestimated FFM in all 4 groups by 2.7 to 4.7 kg; the Kushner equation significantly underestimated FFM by 2.0 to 2.9 kg except in obese women; the Rising equation significantly overestimated FFM in obese women (5.3 kg) and men (2.9 kg); the Khaled equation successfully predicted FFM in all groups except obese men; and the Segal equation successfully predicted FFM in all groups except lean men. In some groups, a portion of the discrepancy could be explained by bias originating from body fat. Analysis of our data by forward regression analysis demonstrated that height2/resistance, body weight, gender and suprailiac skinfold thickness provide the most accurate estimates of FFM (R2=0.92; SEE = 3.58kg) that are free of bias originating from gender and body fat. We conclude that the estimation of fat‐free mass by BR is significantly influenced by gender and obesity. An alternative equation is proposed for estimating fat‐free mass based on measurement of height2/resistance, body weight, gender and suprailiac skinfold thickness.