Background: Bioelectrical impedance analysis (BIA) is simple, inexpensive, portable, safe and relatively accurate means of assessing body composition. However, there were many reports in that the error of BIA was increased in extremely obese subjects. This study was conducted to assess the accuracy of BIA in obese women and to investigate factors that influence the error of BIA in obese women.
Methods: 173 healthy obese women (ages 21 to 49 years; BMI ≥ 25 kg/m2) underwent BIA and dual energy X-ray absorptiometry (DEXA). The accuracy of BIA was assessed by Pearson correlation and Bland-Altman analysis. Factors that influence the error of BIA were investigated by Pearson correlation, one-way ANOVA, and multiple regression analysis.
Results: In obese women, the correlations between estimates of BIA and DEXA were highly significant (r = 0.838~0.910). Compared with DEXA, BIA was highly accurate for fat mass [ΔFM (BIA-DEXA): 0.5 kg (95% confidence interval: -3.8~4.8)], but BIA overestimated fat free mass [ΔFM (BIA-DEXA): 2.8 kg (-1.9~7.5; 95% confidence interval)]. As adiposity was increasing, BIA overestimated fat free mass and underestimated fat mass. Increasing of waist circumference decreased the error of BIA occurred by increasing of adiposity.
Conclusion: In obese women, the correlations and agreements between estimates of BIA and DEXA were highly significant. However, the amount and distribution of body fat had influence on the error of BIA.

Keywords: Bioelectrical impedance analysis, Dual energy X-ray absorptiometry, Body composition, Fat mass, Fat free mass, Obesity