title: Magnitude and variation of ratio of total body potassium to fat-free mass: a cellular level modeling study.
abstract: Potassium is an essential element of living organisms that is found almost exclusively in the intracellular fluid compartment. The assumed constant ratio of total body potassium (TBK) to fat-free mass (FFM) is a cornerstone of the TBK method of estimating total body fat. Although the TBK-to-FFM (TBK/FFM) ratio has been assumed constant, a large range of individual and group values is recognized. The purpose of the present study was to undertake a comprehensive analysis of biological factors that cause variation in the TBK/FFM ratio. A theoretical TBK/FFM model was developed on the cellular body composition level. This physiological model includes six factors that combine to produce the observed TBK/FFM ratio. The ratio magnitude and range, as well as the differences in the TBK/FFM ratio between men and women and variation with growth, were examined with the proposed model. The ratio of extracellular water to intracellular water (E/I) is the major factor leading to between-individual variation in the TBK/FFM ratio. The present study provides a conceptual framework for examining the separate TBK/FFM determinants and suggests important limitations of the TBK/FFM method used in estimating total body fat in humans and other mammals.
authors.affiliation: Obesity Research Center, St. Luke's-Roosevelt Hospital, Columbia University College of Physicians and Surgeons, New York, New York 10025, USA. ZW28@Columbia.edu
authors.forename: Z
authors.initials: Z
authors.lastname: Wang
authors.forename: F X
authors.initials: FX
authors.lastname: Pi-Sunyer
authors.forename: D P
authors.initials: DP
authors.lastname: Kotler
authors.forename: J
authors.initials: J
authors.lastname: Wang
authors.forename: R N
authors.initials: RN
authors.lastname: Pierson
authors.forename: S B
authors.initials: SB
authors.lastname: Heymsfield
mesh_terms: D000273:Adipose Tissue / Q000502:physiology; D000465:Algorithms; D000818:Animals; D001823:Body Composition / Q000502:physiology*; D001835:Body Weight / Q000502:physiology*; D005260:Female; D006801:Humans; D008297:Male; D008954:Models, Biological; D011188:Potassium / Q000378:metabolism*
chemical_list: D011188:Potassium