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Title: What makes a BIA equation unique? Validity of 8-electrode multifrequency-BIA to estimate body compostion in a healthy adult population

Author
item BOSY-WESTPHAL, ANJA - University Of Kiel
item SCHAUTZ, BRITTA - University Of Kiel
item LATER, WIEBKE - University Of Kiel
item KEHAYIAS, JOSEPH - Jean Mayer Human Nutrition Research Center On Aging At Tufts University
item GALLAGHER, DYMPNA - St Luke'S Roosevelt Hospital
item MULLER, MANFRED - University Of Kiel

Submitted to: European Journal of Clinical Nutrition
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/21/2012
Publication Date: 1/1/2013
Citation: Bosy-Westphal, A., Schautz, B., Later, W., Kehayias, J.J., Gallagher, D., Muller, M.J. 2013. What makes a BIA equation unique? Validity of 8-electrode multifrequency-BIA to estimate body compostion in a healthy adult population. European Journal of Clinical Nutrition. 67(S1):S14-S21.

Interpretive Summary: The electrical properties of the body depend on its composition. Simple measurements with electrodes between the hands and the legs can be used to determine the total amount of water in the body and, by extension, lean and fat mass. The method is called bioelectrical impedance analysis (BIA) and the devices used are simple fast and safe. However, the validity of BIA for body composition analysis is limited by assumptions relating to body shape. As the instruments improve, specific prediction equations are developed to translate the electrical measurements into body composition assessment. This is a validation experiment for a modern BIA device which is using eight electrodes (rather than the traditional four) and makes measurements at several electrical current frequencies. Methods BIA equations for the prediction of fat free mass (FFM), total body water (TBW) and extracellular water (ECW) were generated from data obtained on 124 Caucasians using a four-compartment model and dilution techniques as references. The algorithms were validated in an independent multiethnic population (n=130). The validity of BIA results was compared (i) between ethnic groups and (ii) to results from the 4-compartment model and 2-compartment reference methods which used more direct methodology like x-rays and deuterium dilution. The bias between BIA-results and different reference methods was not statistically different between Afro-American, Hispanic, Asian or Caucasian populations. In conclusion, the experiment produced BIA equations that were found independent of the ethnicity of the subjects and therefore expected to be uniformly used in healthy adults.

Technical Abstract: The validity of bioelectrical impedance analysis (BIA) for body composition analysis is limited by assumptions relating to body shape. Improvement in BIA technology could overcome these limitations and reduce the population specificity of the BIA algorithm. BIA equations for the prediction of fat free mass (FFM), total body water (TBW) and extracellular water (ECW) were generated from data obtained on 124 Caucasians (BMI 18.5-35 kg/m2) using a four-compartment model and dilution techniques as references. The algorithms were validated in an independent multiethnic population (n=130). The validity of BIA results was compared (i) between ethnic groups and (ii) to results from the 4-compartment model and 2-compartment methods (air-displacement plethysmography, DXA, and deuterium dilution). Indices were developed from segmental R and Xc values to represent the relative contribution of trunk and limbs to total body conductivity. The coefficient of determination for all prediction equations was high (R2: 0.94 for ECW, 0.98 for FFM and 0.98 for TBW) and RMSE was low (1.9kg FFM, 0.8 l ECW and 1.3kg TBW). The bias between BIA-results and different reference methods was not statistically different between Afro-American, Hispanic, Asian or Caucasian populations and showed a similar difference (-0.2-0.2kg FFM) when compared with the bias between different 2-compartment reference methods (-0.2-0.3kg FFM). An eight-electrode, segmental multifrequency-BIA is a valid tool to estimate body composition in healthy euvolemic adults compared with the validity and precision of other 2-compartment reference methods. Population specificity is of minor importance when compared with discrepancies between different reference methods.