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This Article Full Text Full Text (PDF) All Versions of this Article: 292/1/E49    most recent 00485.2005v1 Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in Web of Science Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via Web of Science (1) Citing Articles via Google Scholar Google Scholar Articles by Wang, Z. Articles by Heymsfield, S. B. Search for Related Content PubMed PubMed Citation Articles by Wang, Z. Articles by Heymsfield, S. B.

Metabolically active portion of fat-free mass: a cellular body composition level modeling analysis

¹Obesity Research Center, St. Luke's-Roosevelt Hospital, Columbia University College of Physicians and Surgeons, New York, New York; and ²Nutrition Consultant, Singapore; ³Mel and Enid Zuckerman Arizona College of Public Health, University of Arizona, Tucson, Arizona

Submitted 5 October 2005 ; accepted in final form 17 March 2006

The proportion of fat-free mass (FFM) as body cell mass (BCM) is highly related to whole body resting energy expenditure. However, the magnitude of BCM/FFM may have been underestimated in previous studies. This is because Moore's equation [BCM (kg) = 0.00833 x total body potassium (in mmol)], which was used to predict BCM, underestimates BCM by 11%. The aims of the present study were to develop a theoretical BCM/FFM model at the cellular level and to explore the influences of sex, age, and adiposity on the BCM/FFM. Subjects were 112 adults who had the following measurements: total body water by ²H₂O or ³H₂O dilution; extracellular water by NaBr dilution; total body nitrogen by in vivo neutron activation analysis; and bone mineral by dual-energy X-ray absorptiometry. FFM was calculated using a multicomponent model and BCM as the difference between FFM and the sum of extracellular fluid and solids. The developed theoretical model revealed that the proportion of BCM to FFM is mainly determined by water distribution (i.e., E/I, the ratio of extracellular to intracellular water). A significant correlation (r = 0.90, P < 0.001) was present between measured and model-predicted BCM/FFM for all subjects pooled. Measured BCM/FFM [mean (SD)] was 0.584 ± 0.041 and 0.529 ± 0.041 for adult men and women (P < 0.001), respectively. A multiple linear regression model showed that there are independent significant associations of sex, age, and fat mass with BCM/FFM.

body cell mass; extracellular water; intracellular water; nutrition status; total body potassium