The human brain is nearly 60% fat.
Why it is true
It is the fattest organ in the human body. This high-fat content is crucial for the myelin sheath, an insulating layer that allows nerve cells to transmit signals rapidly.
Source: Neuroscience
Would you rather be asked first?
This is the reading side of the site, so the answer is in the sentence above — that is the whole point of it. Test yourself works the other way round: the question comes on its own, and the fact and the explanation only appear once you have answered.