Development and Cross-Validation of a Predictive Equation for Fat-Free Mass in Brazilian Adolescents by Bioelectrical Impedance

Abstract

The bioelectrical impedance analysis (BIA) is one of the most commonly used techniques for assessing body composition in a clinical setting and in field approaches, as it has the advantages of easy application, fast, and non-invasive, in addition to its relatively low cost. However, the available predictive equations need to be valid for the evaluated subjects. The aim of this study was to verify the validity of several published BIA equations in estimating fat-free mass (FFM) among Brazilian adolescents, in addition to developing and cross-validating a BIA equation to estimate FFM appropriate for Brazilian adolescents. This is a cross-sectional study with 257 adolescents (128 girls) aged 10–19 years, randomly divided into two groups, namely, development (n = 172) and cross-validation (n = 85). The standard technique for assessing FFM was dual X-ray absorptiometry (DXA). The paired t-test, multiple regression, and the Bland-Altman plots were used to test the validity of the proposed models and to perform cross-validation of the model. The equation derived in this study was as follows: FFM = −17.189 + 0.498 (Height2/Resistance) + 0.226 Weight + 0.071 Reactance − 2.378 Sex + 0.097 Height + 0.222 Age; r2 = 0.92; standard error of the estimate = 2.49 kg; the new equation for FFM showed better agreement when compared with that of the equations developed in other countries. In conclusion, the newly developed equations provide a valid FFM estimation and are recommended for Brazilian adolescents with similar characteristics.

Validity of the relative fat mass pediatric index (RFMp) for the analysis of body composition in physically active youths at different stages of biological maturation

“…In a previous study, Baer et al 31 suggested that, in female children and adolescents, androgen hormone levels were associated with body adiposity profile. Recently, BM was considered as a possible independent variable for the development of an equation to estimate FFM in Brazilian adolescents (10–19 years of age) 6 . Thus, we conjecture that, to estimate body adiposity in children and adolescents, it is necessary to consider the particularities of the BM stages.…”

“…that require compromising the patient's eating habits in the 24 h before the examination, which can compromise the validity of the results if they are erroneously fulfilled. 6,7 Given these limitations, previous research has sought to develop anthropometric indices to predict BF% in different populations of various age groups. 8,9 Among the main indices developed in recent years, the relative fat mass (RFM) developed by Woolcott & Bergman 10 stands out, in which three equations (1: for both sexes; 2: for males; and 3: for females) were developed to identify the BF% in adults of both sexes, and only one equation developed for both sexes proved valid to classify the stage of obesity.…”

Agreement and validity between body fat estimated by skinfold measurement and air displacement plethysmography in adolescents

“…The only study that used ADP as the reference method, estimated body fat from skinfolds obtained by ultrasound (BodyMetrix) in Brazilian adults, and showed moderate reproducibility in men (CCC=0.853), and good reproducibility in women (CCC=0.903) 33 . In relation to studies with Brazilian adolescents, a study evaluated the fat-free mass with BIA and compared measurements with the DXA, which showed good reproducibility (CCC=0,984) 34 . Given these results, the Slaughter equation does not seem to be the most suitable method for assessing body fat.…”

Fat-Free Mass Index, Visceral Fat Level, and Muscle Mass Percentage Better Explain Deviations From the Expected Value of Aortic Pressure and Structural and Functional Arterial Properties Than Body Fat Indexes

“…Finally, despite the fact that two commercial BIA devices (validated and widely used) were used in the present study, it is worth noting that the equations that allowed BIA-derived indexes to be obtained were not derived from studies in the Uruguayan population. As the other authors have done for specific populations in South America (64,65), further studies will allow the equations for obtaining BIA-derived indexes to be evaluated and validated in the Uruguayan population.…”