Development and cross-validation of predictive equations for fat-free mass and lean soft tissue mass by bioelectrical impedance in Brazilian women.

Abstract

Bioelectrical impedance is one of the most used clinical techniques to assess body composition; however, it is necessary that the available predictive equations are valid for the evaluated subjects. This study aimed to develop and cross-validate equations for fat-free mass (FFM) and lean soft tissue mass (LSTM) by bioelectrical impedance for Brazilian women, in addition to test the validity of other available equations. Cross-sectional study with 222 women aged 20-59 years, randomly divided into two groups: development and cross-validation. The standard technique for assessing fat mass, FFM and LSTM was dual energy X-ray absorptiometry. Paired t test, multiple regression, and Bland-Altman plots were used to test the validity of the proposed models, as well as to perform cross-validation of the models. The equations derived in this study were: FFM = 16.284 + 0.442 × (Height2/Resistance) - 0.13 × age + 0.302 × Weight - 0.121 × Waist Circumference; r2 = 0.86; SEE = 2.32 kg; and LSTM = 14.732 + 0.427 × (Height2/Resistance) - 0.125 × age + 0.291 × Weight - 0.115 × Waist Circumference; r2 = 0.92; SEE = 2.29 kg. In addition, the new equation for FFM showed better agreement when compared to another equation developed for a Brazilian population. The newly developed equations provide a valid FFM and LSTM estimation and are recommended for Brazilian women with similar characteristics.