This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: nutrition and digestion, Subject name: Biochemistry
When there is no other source of glucose, liver and muscle glycogen would be exhausted after 
Select and explain. 
A. 12 hours, B. 18 hours, C. 24 hours, D. 36 hours
B: 18 hours
Answer: B: 18 hours 
Explanation: Were there no other source of glucose, liver and muscle glycogen would be exhausted after about 18 hours of fasting. As fasting becomes more prolonged, so an increasing amount of the amino acids released as a result of protein catabolism is utilized in the liver and kidneys for gluconeogenesis. Reference: Harper; 30th edition; Chapter 14; Page no: 149