Final answer:
The missing word in the question is 'body fat', as healthy persons may have up to 5% or 6% of body fat.
Step-by-step explanation:
In the context of the question, the missing word after 'Healthy persons may have up to 5% or 6% of' is 'body fat'.
Water makes up a significant portion of the adult body weight, ranging from 50-70%. However, the percentage varies inversely with the fat content.
For example, lean individuals have about 50% of their body weight as intracellular fluid and 20% as extracellular fluid, while obese individuals have less intracellular fluid and more fat content.