ABSTRACT
By far the most abundant body constituent, water plays a crucial role in all metabolic processes and in the exchange of solutes between the various tissues and the environment. Water represents a very constant 73% of lean body mass in the average human individual. Normally, the daily rate of water intake and generation matches the daily water loss of 2.5 L/day. Water intake includes drinking and eating, as well as water that is generated from metabolism and by the oxidation of carbohydrates, fat, and protein. Constancy of volume or osmolality of body fluids may be threatened by changes in intake or loss of free water, of osmolytes, or a combination of both. Thus, excessive freshwater uptake in drinking leads to hypotonic overhydration characterized by an increase in extracellular fluid (ECF) volume and a decrease in osmolality of the ECF.
