Mechanism of Reduction of Total Body Potassium in Malnutrition

Abstract

Lean Body Mass (LBM) consists of tissues which are metabolically active and are responsible for locomotion. In addition, circulation, respiration and metabolism, are all dependent upon the functional activity of the LBM. It is not surprising, therefore, that in nutritional studies an estimation of LBM becomes of great importance. LBM is the main reservoir of body protein and nitrogen. Unfortunately, direct measurement of total body nitrogen (TBN) was not possible until recently: consequently, indirect methods were used to estimate LBM. Analytical data suggested that in healthy muscle the ratio of intracellular potassium to nitrogen is closely controlled at 3 mM K+ to 1 g nitrogen. This ratio was extrapolated to the whole body measurements by using total body potassium (TBK) as an index of body cell mass (BCM) (Forbes and Hursh, 1963) and calculating LBM from these data. Later prompt gamma analysis (PGA) became available to measure total body nitrogen (TBN) (Mernagh et al., 1977); using these techniques, and also carcass analysis, the ratio of TBK to TBN in normals and in a chronically wasted individual (Knight et al., 1986) was found to be 1.6 mM K+/g nitrogen.