This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Biochemistry
Increased formation of ketone bodies during fasting is a result of which of the following? 
Select and explain. 
A. Increased oxidation of fatty acids as a source of fuel, B. Decreased formation of acetyl CoA in the liver, C. Decreased levels of glucagon, D. Increased glycogenesis in muscle
A: Increased oxidation of fatty acids as a source of fuel
Answer: A: Increased oxidation of fatty acids as a source of fuel 
Explanation: During a fast, catabolism is increased to provide additional sources of energy. This is characterized by increased utilization of fatty acids. When the production of acetyl CoA (produced by enhanced β-oxidation) exceeds the oxidative capacity of the citric acid cycle, ketone bodies are formed. During fasting conditions, glucagon concentrations are increased and glycogenesis is inhibited due to limited energy availability. Acetyl CoA production in the liver is increased due to enhanced β-oxidation.