Agreement between Body Fat Estimation Methods: From Durnin and Womersley Equation to Bioimpedance

Introduction: The Durnin-Womersley equation (DWe) for estimating body fat (%BF) and bioelectrical impedance analysis (BIA) generally give similar results, but in some cases the differences are striking, which could be related to the distribution of fat in some individuals. The objective of this study was to analyze the agreement between both methods and investigate their relationship with the distribution of fat mass. Methods: A sample of 326 individuals (201 women and 125 men), aged between 18 and 74 years, was analyzed. Their %BF was determined by DWe and BIA, using a Tanita RD545 scale. Height, waist, and hip circumferences were also analyzed. Absolute differences between methods (DWe-BIA) were analyzed using simple linear correlation, Bland-Altman analysis, and chi-square tests with GraphPad Prism 8 software. Results: There is high agreement between methods; Bland-Altman analysis showed a mean bias of -1.545 points (-10.58 to 7.49), with a higher proportion of cases in which DWe underestimates the %BF calculated by BIA (approximately 2/3 of cases). The higher the value obtained by BIA, the greater the underestimation of DWe. No association was found between height and DWe-BIA differences. An increment in age was associated with a greater probability of overestimation by DWe. Higher values ​​for waist, hip, and waist/height and hip/height ratios were related to a greater probability of underestimation of %BF by the DWe. Conclusions: The DWe tends to underestimate the %BF in relation to that estimated by BIA, as the latter increases. On the other hand, an increment in waist and hip circumferences also increases the probability that this equation underestimates %BF.