Validation of a three-frequency bioimpedance spectroscopic method for body composition analysis.
OBJECTIVE
We assessed whether whole-body multiple frequency impedance (MFBIA) data obtained at a few discrete frequencies could be used to estimate accurately resistance at 0 (R(0)) and infinite (R(infinity)) frequencies required for prediction of body composition by mixture theory.


METHODS
Fat-free mass (FFM) was measured in 157 subjects (77 males, 80 females; body mass index [BMI] 17.8-41.7 kg/m(2)) by dual X-ray absorptiometry (DXA). Whole-body impedance was measured and R(0) and R(infinity) were calculated by three different methods. FFM predicted using the different values of R(0) and R(infinity) were compared with each other and with the reference DXA values for all subjects stratified according to BMI band (BMI <24.9 kg/m(2), normal weight; BMI 25-29.9 kg/m(2), overweight; BMI >30 kg/m(2), obese).


RESULTS
All BIA procedures predicted an FFM that was slightly but significantly different from DXA-derived values, underestimating by 0.24 to 1.4 kg in the normal-weight subjects and overestimating by 5.3 to 7.1 kg in the obese subjects. Although statistically significant, the different impedance procedures were highly correlated (r > 0.98), with small limits of agreement (approximately +/-2%) when used to predict FFM. Predictive power was associated with BMI, worsening as BMI increased.


CONCLUSIONS
MFBIA can be used to estimate impedance parameters required for mixture theory prediction of body composition, but this approach requires adjustment for BMI to be accurate.
School of Molecular and Microbial Science, University of Queensland, St. Lucia, Brisbane, Australia. l.ward@uq.edu.au
Leigh C
LC
Ward
Julia M
JM
Dyer
Nuala M
NM
Byrne
Kendall K
KK
Sharpe
Andrew P
AP
Hills
D015502:Absorptiometry, Photon / Q000379:methods; D000328:Adult; D001823:Body Composition / Q000502:physiology*; D001827:Body Height / Q000502:physiology; D015992:Body Mass Index; D001835:Body Weight / Q000502:physiology; D017097:Electric Impedance; D005260:Female; D006801:Humans; D008297:Male; D018482:Muscle, Skeletal; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D013057:Spectrum Analysis / Q000379:methods / Q000592:standards*