Which statement best describes the brain's energy use relative to body mass?

• A. 33-66% of daily calories
• B. 5-10% of daily calories
• C. 25-33% of daily calories
• D. 50-75% of daily calories

Answer: (C)

The brain uses energy at a very high rate relative to its small size because neurons are constantly active—maintaining membrane potentials, propagating signals, and recycling neurotransmitters requires a lot of ATP. Most of this energy goes to powering ion pumps that keep neurons ready to fire. Because of this intense demand, the brain consumes a substantial portion of daily calories—about a quarter of the body's energy intake. That’s why the best estimate is roughly 25-33% of daily calories, even though the brain weighs only about 2% of body mass. The other ranges either underestimate or overstate this share relative to the brain’s true metabolic cost.