Enzyme levels which are decreased during starvationa) Fatty acid synthaseb) CoA carnitine transferasec) Citrate lyased) Lipoprotein lipasee) Tyrosine kinase

**Core Concept**
During starvation, the body undergoes a series of metabolic adaptations to utilize stored energy sources. This involves the regulation of various enzymes involved in lipid and carbohydrate metabolism. The correct answer requires an understanding of the key enzymes involved in these pathways and their changes during starvation.

**Why the Correct Answer is Right**
During starvation, the body primarily utilizes stored fat for energy. Fatty acid synthase is an enzyme involved in the synthesis of fatty acids from acetyl-CoA and NADPH. However, during starvation, the body's energy requirements shift towards fatty acid oxidation, not synthesis. As a result, the expression and activity of fatty acid synthase decrease. On the other hand, fatty acid oxidation is enhanced during starvation, which is mediated by enzymes such as CoA carnitine transferase (CPT1). This enzyme plays a crucial role in the transport of long-chain fatty acids into the mitochondria for beta-oxidation.

**Why Each Wrong Option is Incorrect**
* **Option A:** Fatty acid synthase is decreased during starvation because the body's energy requirements shift towards fatty acid oxidation, not synthesis.
* **Option B:** CoA carnitine transferase is actually increased during starvation to facilitate the transport of fatty acids into the mitochondria for oxidation.
* **Option C:** Citrate lyase is involved in the breakdown of citrate to acetyl-CoA, which is increased during starvation to provide substrates for fatty acid oxidation.
* **Option D:** Lipoprotein lipase is involved in the breakdown of triglycerides from lipoproteins, which is increased during starvation to provide substrates for fatty acid oxidation.
* **Option E:** Tyrosine kinase is not directly involved in the metabolic adaptations during starvation.

**Clinical Pearl / High-Yield Fact**
During starvation, the body's energy requirements shift towards fatty acid oxidation, which is mediated by enzymes such as CoA carnitine transferase. Understanding the regulation of these enzymes is crucial for managing patients with metabolic disorders.

**Correct Answer:** A. Fatty acid synthase