Assessment of body composition in subjects with metabolic syndrome comparing single-frequency bioelectrical impedance analysis and bioelectrical spectroscopy.

Background: The aim of this study was to investigate the agreement between body composition measurements made with two methods-single-frequency bioelectrical impedance analysis (SF-BIA) and bioelectrical impedance spectroscopy (BIS). Methods: The body composition measurements using SF-BIA and BIS were performed seven times during 6 months on 41 patients (13 men and 28 women) with metabolic syndrome who were taking part in a dietary intervention study. Results: The mean [standard deviation (SD)] fat mass (FM) and median [interquartile range (IQR)] FM% measured with SF-BIA were 32.7 (6.7) kg and 36.3 (30.3-39.3)%, respectively, compared with 38.2 (8.7) kg and 40.9 (35.5-45.6)%, respectively, using BIS. The median (IQR) fat-free mass (FFM) was 60.0 (53.3-73.5) kg according to SF-BIA and 55.4 (48.8-66.5) kg according to BIS. These results obtained with the two methods were significantly different (P<0.001). Still highly significant correlations were found between the results obtained with SF-BIA and BIS for FM and FFM (all r >= 0.89, P<0.001). Using Bland-Altman analysis, the bias was found to be -5.4 (4.1) kg for FM, -5.5 (3.7)% for FM%, and 5.4 (4.1) kg for FFM. Rather wide limits of agreement were found for FM, FM%, and FFM. Conclusion: Body composition data obtained using SF-BIA and BIS in subjects with metabolic syndrome were highly correlated but not interchangeable. FM was systematically lower when using SF-BIA than when using BIS.