This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Carbohydrates, Subject name: Biochemistry
[{'content': 'Choose the major fuel that is being adapted by the brain after 1 week of fasting. \nSelect and explain. \nA. Ketone bodies, B. Blood glucose, C. Fatty acids, D. Glycogen', 'role': 'user'}, {'content': "Answer: A \nExplanation: The brain then takes up and oxidizes the ketone bodies to derive energy. Consequently, the brain decreases its use of glucose, although glucose is still a major fuel for the brain.Ketone bodies are used by the brain after 3 to 5 days of fasting. This is done to spare protein degradation to provide carbons for gluconeogenesis. Approximately 60% of the brain's energy needs will still be dependent on glucose, but the other 40% can be realized from ketone body oxidation. The brain will not oxidize fatty acids because they have trouble crossing the blood-brain barrier, and the brain has very low levels of glycogen.", 'role': 'assistant'}]