Increased formation of ketone bodies during fasting is a result of:
**Core Concept**
The question tests the understanding of the metabolic shift that occurs during fasting, specifically the increase in ketone body formation. During fasting, the body adapts to utilize alternative energy sources, primarily fatty acids, to compensate for the lack of glucose.
**Why the Correct Answer is Right**
When fasting, the liver increases the activity of hormone-sensitive lipase, leading to the breakdown of triglycerides into free fatty acids and glycerol. The free fatty acids then undergo beta-oxidation, producing acetyl-CoA, which is subsequently converted to acetoacetate and then to ketone bodies (acetoacetate, beta-hydroxybutyrate, and acetone) by the enzyme HMG-CoA synthase. This metabolic shift is mediated by the decrease in insulin levels and the increase in glucagon levels, which activates the enzyme HMG-CoA synthase.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it does not accurately describe the metabolic shift that occurs during fasting. While it is true that fatty acid synthesis is decreased during fasting, this is not the primary mechanism by which ketone body formation increases.
**Option B:** This option is incorrect because it does not accurately describe the role of insulin in regulating ketone body formation. Insulin actually decreases ketone body formation by inhibiting the enzyme HMG-CoA synthase.
**Option C:** This option is incorrect because it does not accurately describe the role of glucagon in regulating ketone body formation. Glucagon actually increases ketone body formation by activating the enzyme HMG-CoA synthase.
**Clinical Pearl / High-Yield Fact**
During prolonged fasting, the brain can adapt to use ketone bodies as a primary energy source, reducing the reliance on glucose and potentially reducing the risk of hypoglycemia.
**Correct Answer:** C. The increase in glucagon levels and the activation of the enzyme HMG-CoA synthase are key factors in the increased formation of ketone bodies during fasting.