New insights into body composition assessment in obese women.

During treatment of patients with non-insulin-dependent diabetes mellitus, there may be marked body weight loss. Therefore, body composition should be monitored to check for a decrease in fat mass alone, without an excessive decrease of both fat-free mass and total body water. Accordingly, it is useful to monitor the hydration of these patients. One method that allows us to check the status of body hydration is the multifrequency bioelectric impedance analysis (MFBIA). It makes use of formulas that estimate total body water on the basis of the concept that the human body may be approximated to a cylinder of length equal to body height. In normal subjects body water estimates are sufficiently accurate, but in obese subjects the true hydration status may be overestimated. In this report, we describe the accuracy of mathematical models previously described in the literature, and correct for the overestimation of total body water in obese subjects by means of a new equation based on a new model. The coefficients for each model have been recalculated by the weighing of our sample in order to test the accuracy of estimates obtained with the equations. This new model includes both body volume and two impedances at appropriate frequencies useful for identifying two terms strictly related to extra- and intra-cellular water. The new formulas do not include body weight, but they include the body volume, a parameter more closely related to the biophysical reference model. Fifty-five overweight females, body mass index ranging from 26.8 to 50.2 kg/m2, were enrolled in the study. The proposed equations, taking advantage of two impedance values at appropriate frequencies, better predict total body water in obese women. This was particularly evident when the results obtained with the multifrequency bioelectric impedance analysis and deuterium isotopic oxide dilution method were compared. Although this last method is considered the "gold standard," it is not suitable for use in routine clinical practice. In conclusion, evaluation of total body composition by means of bioelectric impedance analysis might be included in programs for the prevention of non-insulin-dependent diabetes and for monitoring weight loss during overt pathology.