Measurement of body composition changes during weight loss in obese men using multi-frequency bioelectrical impedance analysis and multi-compartment models

Background: The accurate measurement of changes in body composition is important to assess the contribution of fat and fat free mass to total body mass change as a measure of the effectiveness of weight loss programmes. Bioelectrical impedance spectroscopy (BIS) is a rapid and non-invasive technique which could be applied to assess body composition changes. The aim of the study was to evaluate the accuracy of the BIS for the measurement of fat mass (FM), total body water (TBW) and extracellular water (ECW) changes induced by different degrees of caloric deficit in obese men. Methods: Three groups of six, obese men participated in either (i) a total fast (for 6 days); (ii) a VLCD (2.5 MJ/day for 3 weeks); or (iii) LCD (5.2 MJ/day for 6 weeks). FM was measured using a 4-compartment (4-C) model. TBW and ECW were determined by dilution methods, respectively. TBW, ECW and FM were also assessed with BIS. Results: Body weight loss in the fasting group was 6.0 ± 1.3 kg over 6 days; the VLCD group lost 9.2 ± 1.2 kg over 21 days and the LCD group lost 12.6 ± 2.4 kg over 42 days. BIS underestimated FM changes (bias = -3.3 ± 3.8 kg) and overestimated changes in TBW and ECW by +1.8 ± 4.8 kg and +2.3 ± 6.4 kg, respectively. The measurement error was consistently larger in the fasting group and the magnitude of the bias interacted significantly with the rate of weight loss. Conclusion: Rapid weight loss affects the accuracy of the BIS in detecting changes in body composition. A careful interpretation of the results is needed when sizable changes in body water compartments occurs. © 2012 Asian Oceanian Association for the Study of Obesity.