Validação de diferentes equações para predição da massa livre de gordura através da bioimpedância elétrica em idosos do sul do Brasil

Abstract

Bioelctrical impedance analysis (BIA) is one of the most used methods for estimating body composition because it is relatively inexpensive, easy to use, portable and noninvasive compared to other reference methods. It is a doubly indirect method, this means that fat free mass (FFM) and fat mass (FM) are estimated from a reference method, such as dual energy X-ray absorptiometry (DXA) or resonance, by a predictive equation that uses BIA data. The method is affected by several physiological situations, such as electrolyte concentration, limb length and body water distribution. This requires specific equations, especially for gender and ethnicity. BIA would be the ideal method for evaluating body composition for use in the elderly, as this population undergoes a change in their body compartments. These changes may be associated with the onset of chronic diseases due to increased fat mass, in addition to sarcopenia, loss of strength and muscle mass. This has motivated the development of elderly-specific BIA equations in recent years. Thus, the objective of this study was to test the validity of the recently developed equation for the Brazilian adult population to predict FFM in an elderly population of the city of Pelotas - RS. For this, we used secondary data from a subsample with elderly aged 10 years or older (N = 192), collected from March to October 2014, in a cross-sectional study. For the present study we used data on gender, age, ethnicity, weight, height, body mass index, resistance and reactance obtained from a singlefrequency BIA device. These values were then applied to the gender-specific predictive Brazilian equation of FFM. The DXA derived FFM of the elderly was used as a reference for the validation of the Brazilian BIA equation and these values were compared with equations developed for other specific ethnicities for the elderly. Data were analyzed in the STATA 14.2 statistical package. The comparison of the FFM values (in kilograms) found from the Brazilian equation and the Deurenberg and Roubenoff equations were performed using the paired t-test, as well as evaluation of precision and accuracy, having as reference method the values obtained from DXA. Lin's correlation correlation coefficient was also evaluated, as well as estimates of agreement limits from the Bland-Altman plots. The results showed a good accuracy regarding the use of the Brazilian equation applied to its population, since there was adequate population representativeness of the evaluated sample, when compared to the other equations. Thus, it can be used as a prediction of FFM in the Brazilian elderly, contributing to the prognosis of these individuals.