**Core Concept**
Insulin plays a crucial role in regulating glucose and lipid metabolism. Insulin promotes lipogenesis, the process of converting glucose into fatty acids and subsequently into triglycerides, which are stored in adipose tissue. This process involves the activation of key enzymes and the inhibition of certain pathways.

**Why the Correct Answer is Right**
Insulin stimulates lipogenesis by promoting the activity of acetyl-CoA carboxylase (ACC), a key enzyme in the biosynthesis of fatty acids. This is achieved by increasing the translocation of glucose transporter 4 (GLUT4) to the cell surface, allowing glucose to enter the cell. Once inside, glucose is converted to glucose-6-phosphate, which is then converted to pyruvate. Pyruvate is then converted to acetyl-CoA, which is the substrate for ACC. Insulin also decreases the activity of hormone-sensitive lipase (HSL), which is responsible for the breakdown of triglycerides. Moreover, insulin decreases the intracellular cAMP level, which activates protein kinase A (PKA) and subsequently inhibits ACC.

**Why Each Wrong Option is Incorrect**

**Option A:** Increasing acetyl-CoA carboxylase activity is actually a mechanism by which insulin promotes lipogenesis, not a mechanism by which insulin does not promote lipogenesis.

**Option B:** Increasing the transport of glucose into the cells is a mechanism by which insulin promotes lipogenesis, as glucose is a precursor for fatty acid synthesis.

**Option D:** Decreasing intracellular cAMP level is a mechanism by which insulin promotes lipogenesis, as it inhibits the activity of PKA and subsequently activates ACC.

**Clinical Pearl / High-Yield Fact**
It is essential to remember that insulin promotes lipogenesis by increasing the activity of ACC and decreasing the activity of HSL. This is in contrast to glucagon, which promotes lipolysis, the breakdown of triglycerides.

**✓ Correct Answer: C. Inhibits pyruvate dehydrogenase**