Evaluation of the novel Tanita body-fat analyser to measure body composition by comparison with a four-compartment model

The Tanita body-fat analyser is a novel device to estimate body fat, based on the principles of bioelectrical impedance. It differs from other impedan ce systems which use surface electrodes in that the subjects stand bare-foo ted on a metal sole-plate which incorporates the electrodes, hence impedanc e is measured through the legs and lower trunk. In 104 men and 101 women (1 6-78 years and BMI 16-41 kg/m(2)) the mean bias in body-fat mass measured u sing the Tanita body-fat analyser was 0.8 (2SD 7.9) kg relative to a four-c ompartment model. This is comparable to the other prediction techniques tes ted (conventional tetrapolar impedance -1.3 (2SD 6.9) kg, skinfold thicknes ses 0.3 (2SD 7.4) kg, and BMI-based formulas -0.2 (2SD 9.0) kg and -0.6 (2S D 8.5) kg), but the agreement was poorer than for 'reference' methods to me asure body fat (density 0.2 (2SD 3.7) kg, total body water -0.9 (2SD 3.4) k g and dual-energy X-ray absorptiometry 0.1 (2SD 5.0) kg). The present paper also describes the derivation of a new prediction equation for the calcula tion of body composition from the Tanita body-fat analyser. The equation in corporates sex, age, and a log-transformation of height, weight and the mea sured impedance to predict body fat measured by a four-compartment model. T his approach is recommended in the derivation of other prediction equations in body composition analysis. Using this novel prediction equation the res idual standard deviations were 4.8 % for men and 3.3 % for women. A similar analysis using data collected with a conventional tetrapolar system yielde d residual standard deviations of 4.3 % for men and 3.1 % for women. This d emonstrates that the practical simplicity of the novel Tanita method is not associated with a clinically significant decrement in performance relative to a traditional impedance device.