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.