How much of total body mass is taken up by fluids in a normal healthy adult?

In a normal healthy adult, fluids account for about 45 to 60% of total body mass. This percentage includes the sum of intracellular fluid, which constitutes about two-thirds of the total body water, and extracellular fluid, which accounts for the remaining one-third. These fluid compartments are crucial for various physiological functions, including maintaining blood volume, regulating temperature, and facilitating cellular processes.

The percentage can vary based on factors such as age, sex, and body composition; for instance, individuals with higher fat content may have a lower percentage of body water, given that fat tissue contains less water than lean tissue. Understanding this range helps healthcare professionals assess hydration status and manage fluid therapy effectively in clinical settings.