Question

Total body water (TBW) in infants is how much of body weight :

• A. 50%
• B. 65% - 75%
• C. 50% - 55%
• D. 60%

Hint:

A solid rule of thumb for clinical exams: As humans age, their body fat percentage generally increases, and therefore their TBW progressively decreases. The hierarchy is: Infants (highest, ~70%) $>$ Adult Males (~60%) $>$ Adult Females (~55%) $>$ Elderly individuals (~50%).

Answer 1

The Correct Option is B

Step 1: Concept:
The question tests clinical physiological knowledge regarding the percentage of total body water (TBW) relative to total body weight, and how this composition specifically changes during human development, particularly in infants.

Step 2: Step-by-step Explanation:

• Total body water is a dynamic physiological metric that fluctuates significantly throughout a human's lifespan. It is inversely correlated with the amount of adipose (fat) tissue in the body, because fat tissue contains very little water compared to muscle and organs.

• In a healthy, average adult male, TBW makes up approximately 60% of their total body weight.

• In a healthy adult female, due to a naturally higher proportion of essential adipose tissue, TBW is comparatively lower, usually sitting around 50% to 55%.

• Infants, particularly newborns and neonates, possess a drastically different body composition. They have very little body fat, a lower proportion of dense bone mass, and a remarkably high extracellular fluid volume.

• Because of this unique composition, full-term healthy infants have a much higher TBW percentage, typically ranging from 65% to 75% of their total body weight. Premature infants can exhibit an even higher water composition, sometimes reaching up to 80%.

Step 3: Final Answer:
Infants contain roughly 65% - 75% body water relative to their weight.