Final answer:
During starvation, the main source of energy for the brain is ketone bodies.
Step-by-step explanation:
During starvation, the main source of energy for the brain is ketone bodies. When the body is deprived of nourishment for an extended period of time, it goes into survival mode. The first priority is to provide enough glucose or fuel for the brain, so the body uses ketones to meet the brain's energy needs. This allows the brain to continue functioning even when glucose levels are very low. Fatty acids and triglyceride stores are used to create ketones, preventing the breakdown of proteins that serve as carbon sources for gluconeogenesis.