P36 Validity of segmental bioelectrical impedance analysis in estimating body composition

Bioelectrical impedance analysis (BIA) measures the impedance and resistance associated with passage of an alternating current through the body. The aforementioned are proportional to total body water (TBW) and therefore can be used to provide expedient estimates of body composition. However, little validity information is available for popular commercially available bathroom scale type devices which perform segmental measurements (lower limbs). The aim of this study was therefore to compare body composition estimates between a commercially available easy to use segmental BIA device (Tanita BC-532, Tanita Corp, Tokyo, Japan) and criterion values in a group (n = 9) of healthy males (mean ± SD: 48.6 ± 18.8 yr; 173.8 ± 4.5 cm; 72.8 ± 8.9 kg). Criterion four compartment body composition determinations involved measures of body density, TBW and bone mineral mass. The results (mean ± SD) are summarised below:

While the mean %BF and fat free mass values for both methods were not significantly different, considerable intra- individual differences were observed. BIA values varied from the four compartment values by -3.0 to 4.4% BF and - 3.3 to 1.9 kg fat free mass. The BIA estimates of TBW were significantly different from the criterion measures and intra-individual differences displayed a large range of -0.6 to 3.6 kg. Significant underestimations of TBW via BIA are concerning given that this is the parameter initially established by this method. Furthermore, the BIA data resulted in a FFM hydration value of 68.5% which was significantly (P<0.001) lower than the four compartment value of 72.0%. Presumably the BIA algorithms use an assumed FFM hydration value to determine body composition. In conclusion, the BIA device tested displayed poor individual accuracy for the estimation of body composition compared with a criterion method.