Background/objectives: Obesity, pregnancy and lactation all affect body composition. Simple methods to estimate body composition are useful in clinical practice and to evaluate interventions. In overweight and obese lactating women, such methods are not fully validated. The objective of this study was to validate the accuracy and precision of bioimpedance spectroscopy (BIS) by Xitron 4200 and 8-electrode multifrequency impedance (multifrequency bioimpedance analysis, MFBIA) by Tanita MC180MA with the reference methods dual energy X-ray absorptiometry (DXA) and doubly labeled water (DLW) for the assessment of body composition in 70 overweight and obese women postpartum.
Subjects/methods: The LEVA-study (Lifestyle for Effective Weight loss during lactation) consisted of an intervention and follow-up with three assessments at 3, 6 and 15 months postpartum, which made possible the validation of both accuracy and precision. Mean differences between methods were tested by a paired t-test and Bland-Altman plots for systematic bias.
Results: At baseline, BIS and MFBIA underestimated fat mass (FM) by 2.6±2.8 and 8.0±4.2 kg compared with DXA (P<0.001) but without systematic bias. BIS and MFBIA overestimated total body water (TBW) by 2.4±2.2 and 4.4±3.2 kg (P<0.001) compared with DLW, with slight systematic bias by BIS. BIS correctly estimated muscle mass without systematic bias (P>0.05). BIS overestimated changes in TBW (P=0.01) without systematic bias, whereas MFBIA varied greatly and with systematic bias.
Conclusions: BIS underestimates mean FM compared with DXA but can detect mean changes in body composition, although with large limits of agreement. BIS both accurately and precisely estimates muscle mass in overweight and obese women postpartum. MFBIA underestimates FM and overestimates TBW by proprietary equations compared with DXA and DLW.