Brain represents 2% of our body weight, but it accounts for 20% of our energy use

While the brain represents just 2% of a person’s total body weight, it accounts for about 20% of the body’s energy use.

Source: Raichle ME, Gusnard DA. Appraising the brain's energy budget. Proc Natl Acad Sci U S A. 2002;99(16):10237-10239. doi:10.1073/pnas.172399499