Brain Metabolism

The brain must generate ATP in large quantities to maintain the membrane potentials essential for transmission of nerve impulses. Under normal conditions the brain uses only glucose to meet its prodigious energy requirements, which amounts to about 60% of the glucose utilization of a human at rest. The brain's need for about 120 grams of glucose per day is equivalent to 1760 kJ-about 15% of the total energy consumed each day. The brain's quantitative requirement for glucose remains quite constant, even when an animal is at rest or asleep.

The brain is a highly aerobic organ, too, and its metabolism utilizes some 20% of the total oxygen consumed by a human. Because the brain has no significant glycogen or other fuel reserves, the supply of both oxygen and glucose cannot be interrupted, even for a short time. Otherwise, anoxic brain damage results. However, the brain can adapt during fasting to use ketone bodies instead of glucose as a major fuel.