Validation of bioelectrical impedance for the prediction of fat-free mass in brazilian elderly subjects

Abstract

Aging involves both nutritional and physiological changes, reducing fat-free mass (FFM) and increasing body fat, both of which are associated with physical weakness, unfitness and morbidity among the elderly. This study was undertaken to analyze the cross-validity of bioelectrical impedance equations for the prediction of fat-free mass (FFM) in elderly Brazilians. A cross-sectional population-based study, was performed in Florianópolis, Santa Catarina, Brazil, 2006. The study sample comprised 60 men and 120 women, aged 60 to 81. The dual energy X-ray absorptiometry (DEXA) served as gold standard. Predicted %BF and FFM were obtained from various anthropometric equations and bioelectric impedance. The cross-validation criteria suggested by Lohman and Bland-Altman plots of differences against the mean were used. The body mass index of the sample ranged from 18.4 to 39.3 kg/m(2). Mean percent body fat was 23.1 +/- 5.8% in men and 37.3 +/- 6.9% in women (range: 6 to 51.4%). In men, the equations of Kyle et al. (2001), Dey et al. (2003) and Sun et al. (2003) did not differ significantly from the DEXA measurement, with a constant error (CE) of 0.7 to 2.5 kg. In contrast, among women only the equations of Kyle et al. (2001) and Dey et al. (2003) were found to be valid (CE: 0.3 to 2.7 kg). The bioelectrical impedance equations validated in this study can be used in the Brazilian elderly population.