Body composition: validity of segmental bioelectrical impedance analysis

Bioelectrical impedance analysis (BIA) measures the impedance associated with passage of an alternating current through the body which is proportional to total body water (TBW) and therefore can provide expedient estimates of body composition. However, little validity information is available for commercially available bathroom scale type devices which perform whole body estimates from segmental (lower limb) measurements. This study therefore compared body composition estimates between a commercially available segmental BIA device (Tanita BC-532) and four compartment criterion values. Body composition of nine males and nine females (mean +/- SD: 37.7 +/- 18.7 yr; 170.7 +/- 5.3 cm; 68.38 +/- 9.7 kg) was determined via BIA and a four compartment model incorporating measures of body density, TBW and bone mineral mass. While the mean %BF and fat free mass (FFM) 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 FFM. The BIA estimates of TBW were significantly different from the criterion measures and intra-individual differences displayed a large range (-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%. In conclusion, the BIA device tested displayed poor individual accuracy for the estimation of body composition compared with a four compartment criterion method.