Validity and reliability of bioelectrical impedance analysis to estimate body fat percentage against air displacement plethysmography and dual‐energy X‐ray absorptiometry

Abstract

Abstract Air displacement plethysmography ( ADP ) and dual‐energy X‐ray absorptiometry ( DXA ) are well‐regarded methods for predicting body fat percentage ( BF %). Bioelectrical impedance analysis ( BIA ) also predicts BF % and has distinct advantages in research settings. Aim To assess the validity of BIA against ADP and DXA to measure BF %, and to test the reliability of each method. Methods Adults ( n = 166) with a wide range of body mass index (19–38 kg/m 2 ) were tested twice during a 5‐day period. ADP was conducted in a BodPod (Life Measurement Inc, Concord, CA , USA ); DXA measurements on a QDR D iscovery A (Hologic) and BIA measurements used the InBody 230 (Biospace Ltd., Seoul, Korea). Agreement between measurements was analysed using t ‐tests, effect size, linear regression models and method of triads (estimating true value). Results BIA showed excellent relative agreement to the estimated true value (ρ = 0.97 (0.96, 0.98)) and to ADP (R 2 = 0.88) and DXA (R 2 = 0.92), but wide limits of agreement (−4.25 to 8.37%). BIA underestimated BF % by 2%, across all values. DXA showed excellent relative agreement to the estimated true value (ρ = 0.97 (0.96, 0.98)) and with ADP (R 2 = 0.92), good absolute agreement but wide limits of agreement (−6.13 to 6.91%) and under‐ and overestimation at high and low BF % levels, respectively. All methods showed excellent reliability with repeat measurements differing by less than 0.2% with very small 95% CIs . Conclusions BIA may be a valid method in research and population samples. All three methods showed excellent reliability.