Submitted to: North Dakota Academy of Science Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 3/20/2000
Publication Date: 4/28/2000
Citation: Lukaski, H.C., Siders, W.A., Hall, C.B. 2000. Evaluation of regional bioelectrical impedance measurements to assess whole body composition. Proceedings of the North Dakota Academy of Science. 54:38.
Interpretive Summary: Findings of research studies that validate the bioelectrical impedance method and the practical nature of this method have encouraged the development of devices for at-home assessment of body composition. One commercial application relies on the use of measurements of lower body impedance to estimate whole body fat-free mass. We measured whole body and lower body impedance and reference body composition with dual x-ray absorptiometry. Lower body measures of impedance significantly over predicted whole body fat-free mass by more than 10%. We attribute this difference to errors in the assumption that the amount of conductor or fat-free mass is similar in all people because the variability in the ratio of upper to lower body ranged from 47 to 55%. Thus, the ease of measuring regional bioelectrical impedance is offset by the errors in predicting body composition in humans. This information will be useful to dietetics professionals and counselors who seek to use bioelectrical impedance to monitor body composition of individuals.
Technical Abstract: This study examined the hypothesis that regional bioelectrical impedance (BI) measurements are valid predictors of whole body fat-free mass (FFM). Fifteen healthy women aged 33 to 86 years underwent measurements of BI by using spot electrodes positioned either on the right hand and ankle for whole body and right and left ankle for lower body determinations. Reference body composition was assessed by using dual x-ray absorptiometry. Although lower body and whole body BI measurements were correlated (r=0.70, p<0.03), they were significantly different (583+/-13 and 509+/-13 ohm, respectively). DXA measurements of whole and lower body FFM were significantly different (40.72+/-1.79 vs 20.71+/-0.91 kg). Impedance predictions of whole body FFM calculated by using lower body BI measurements were significantly greater than estimates derived from whole body BI measurements (47.06+/-1.95 vs 43.79+/-1.41 kg). As compared to DXA measurements, lower body BI over predicted FFM more than whole body BI (6.34+/-1.48 vs 3.07+/-0.71 kg) and these differences were both significantly different than 0. The errors in the prediction of whole body FFM from lower body BI measurements were not related to either the size of the FFM or the ratio of lower body to whole body FFM which ranged from 47 to 55%. These findings suggest that lower body measurements of BI are not predictive of whole body FFM. Furthermore, the practicality of measuring lower body BI is outweighed by the lack of validity of this approach to assess FFM.