[Formulation of an equation to predict fat mass using bioelectrical impedance in adults in a wide range of ages and body mass index].

BACKGROUND Bioelectrical impedance (BIA) has a good correlation and agreement with reference techniques, such as dual energy X-ray absorptiometry (DEXA), to assess body composition. AIM To develop and assess the concordance of an equation to predict body fat mass derived from anthropometric data, gender, age and resistance obtained from bioelectrical impedance in adults, using DEXA as the reference method. PATIENTS AND METHODS Cross-sectional study of 62 women and 59 men aged 18 to 64 years with a body mass index ranging from 18.5 to 34.8 kg/ m². The equation was constructed using a predictive statistical model, considering sex, age, weight, resistance index (height²(cm)/ resistance (ohms)), as independent variables, and fat mass as the dependent variable. RESULTS The R² of the regression model was 0.96, and the standard error of estimation was 2.58 kg (p < 0.001). When comparing with DEXA, no significant differences were observed for the estimation of FM, between the equation developed in this work and that proposed by the manufacturer of the BIA equipment. However, the latter equation, underestimated FM by -2.5 ± 9.5% (p > 0.05) and - 4.5 ± 8,9% (p < 0.05) in both genders and in women, respectively. CONCLUSIONS The concordance between estimation of fat mass by the formula developed in this work and by DEXA was better than the estimation obtained using the formula proposed by the manufacturer of the BIA equipment.