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

Zi Mian Wang, Stanley Heshka, Jack Wang, Dympna Gallagher, Paul Deurenberg, Zhao Chen, Steven B. Heymsfield

Research output: Contribution to journalArticlepeer-review

33 Scopus citations


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.

Original languageEnglish (US)
Pages (from-to)E49-E53
JournalAmerican Journal of Physiology - Endocrinology and Metabolism
Issue number1
StatePublished - Jan 2007


  • Body cell mass
  • Extracellular water
  • Intracellular water
  • Nutrition status
  • Total body potassium

ASJC Scopus subject areas

  • Endocrinology, Diabetes and Metabolism
  • Physiology
  • Physiology (medical)


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