Bioelectrical impedance analysis (BIA) has been proposed for
measuring fat-free mass, total body water, percent fat, body
cell mass, intracellular water, and extracellular water: a veritable
laboratory in a box. Although it is unlikely that BIA is quite
this versatile, correlations have been demonstrated between
BIA and all of these body compartments. At the same time, it
is known that all of the compartments are correlated among themselves.
Because of this, it is difficult to determine whether BIA is
specific for any or all of these compartments. To investigate
this question, we induced acute changes in total body water
and its compartments over a 3-h period. Using this approach,
we demonstrated that multifrequency BIA, using the Cole-Cole
model to calculate the zero frequency and infinite frequency
resistance, measures extracellular and intracellular water.
