Comparison of D2O and ethanol dilutions in total body water measurements in humans

Total body water was measured by ethanol dilution and D2O stable isotope dilution in a group of 20 healthy volunteers (5 females and 15 males), predominantly 23- to 31-year-old students. Both indicator substances were given orally with an ethanol burden of 0.8 g/kg body weight and a D2O burden of 0.1 g/kg body weight after 12-h food and fluid restriction. This first direct comparison of total body water (TBW) from ethanol and D2O dilutions revealed the ethanol compartments to be smaller than those of D2O. The quotient of TBW (ethanol)/TBW (D2O) was 97.7%, which is the order of the quotient TBW (H2(18)O)/TBW (D2O) ( = 97%), well known from the literature and taken to represent relatively exactly the value of TBW overestimation (based on H/D exchange for acid protons) following D2O dilution [36]. Thus the value of TBW (ethanol) is almost identical to that of H2(18)O, which provides direct evidence that ethanol is distributed only in the body water.