1. ^*Obesity Research Center, St. Luke's-Roosevelt Hospital, Columbia University College of Physicians and Surgeons and Institute of Human Nutrition, New York, New York
2. ^†Pediatric Unit, Verona University Medical School, Verona, Italy

Correspondence: Steven B. Heymsfield, Weight Control Unit, 1090 Amsterdam Avenue, 14th Floor, New York, NY 10025. E-mail: SBH2@Columbia.edu

^**The costs of publication of this article were defrayed, in part, by the payment of page charges. This article must, therefore, be hereby marked "advertisement" in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.

Received 15 April 2004; Accepted 3 November 2004.

Abstract

Objective: The aim of this study was to develop and compare two DXA-based four-compartment [body weight = body cell mass (BCM) + extracellular fluid (ECF) + extracellular solids (ECS) + fat] cellular level models.

Research Methods and Procedures: Total body potassium (TBK) model: BCM from TBK by whole-body counting—ECF_TBK = LST - [BCM_TBK + 0.73 osseous mineral (Mo)]. Bromide model: ECF from sodium bromide dilution—BCM_BROMIDE = LST - (ECF_BROMIDE + 0.73 Mo); Mo and LST measurements came from DXA. The two approaches were evaluated in 99 healthy men and 118 women.

Results: BCM estimates were highly correlated (r = 0.97, p < 0.001), as were ECF estimates (r = 0.87, p < 0.001); a small statistically significant mean difference was present (mean SD; BCM_TBK model, 30.4 8.9 kg; BCM_BROMIDE, 31.4 9.3 kg; = 1.0 2.8 kg; p < 0.001; ECF_TBK, 18.5 4.2 kg; ECF_BROMIDE, 17.5 3.6 kg; = 1.0 2.8 kg; p < 0.001). A high correlation (r = 0.97, p < 0.001) and good agreement (38.9 9.5 vs. 38.9 9.5 kg; = 0.0 2.4 kg; p = 0.39) were present between TBW, derived as the sum of intracellular water from TBK and ECW from bromide, and measured TBW by ²H₂O dilution.

Discussion: Two developed four-compartment cellular level DXA models, one of which is appropriate for use in most clinical and research settings, provide comparable results and are applicable for BCM and ECF estimation of subject groups with hydration disturbances.