**Core Concept**
During fasting state, the body undergoes a shift from glucose-dependent metabolism to fat-dependent metabolism to maintain energy homeostasis. This involves the activation of various enzymes involved in lipolysis, ketogenesis, and gluconeogenesis to ensure a continuous supply of energy.

**Why the Correct Answer is Right**
Acetyl CoA carboxylase (ACC) is a key enzyme involved in the carboxylation of acetyl-CoA to malonyl-CoA, which is a precursor for fatty acid synthesis. In the fasting state, the body's priority is to utilize stored fat for energy, rather than to synthesize new fat. Therefore, the activity of ACC is decreased, not increased, to prevent the synthesis of new fatty acids. This is in contrast to other enzymes involved in gluconeogenesis and ketogenesis, which are indeed activated in the fasting state.

**Why Each Wrong Option is Incorrect**
**Option B:** Carnitine acyl transferase (CAT) is involved in the transport of fatty acids into the mitochondria for beta-oxidation, which is increased in the fasting state to utilize stored fat for energy.
**Option C:** Phosphoenolpyruvate carboxykinase (PEPCK) is a key enzyme in gluconeogenesis, which is activated in the fasting state to maintain blood glucose levels.
**Option D:** Pyruvate carboxylase is also involved in gluconeogenesis and is activated in the fasting state to produce glucose from non-carbohydrate sources.

**Clinical Pearl / High-Yield Fact**
In the fasting state, the body's reliance on fat for energy leads to the production of ketone bodies, which can be used as an alternative source of energy for the brain and other organs. This process is critical for maintaining energy homeostasis during periods of fasting or starvation.

**✓ Correct Answer: A. Acetyl CoA carboxylase**