Fatty acid synthesis is activated during which of the following situations?

Fatty acid synthesis is primarily regulated by the availability of substrates and the hormonal environment within the body. In particular, high levels of citrate and insulin are significant indicators that promote the synthesis of fatty acids.

When carbohydrate intake is sufficient, glucose metabolism increases, leading to elevated levels of acetyl-CoA. This acetyl-CoA is often converted into citrate in the mitochondria, which can then be transported into the cytosol. High levels of citrate signal that the energy status in the cell is robust, indicating an ample supply of substrates for lipogenesis.

Insulin plays a crucial role in this process as well. It is a key anabolic hormone that promotes the uptake of glucose and inhibits the breakdown of fatty acids. Elevated levels of insulin, particularly after a carbohydrate-rich meal, enhance the activity of enzymes involved in fatty acid synthesis, such as acetyl-CoA carboxylase.

Conversely, elevated glucagon levels, which typically arise during fasting or low carbohydrate intake, signal the body to utilize stored fat for energy. This hormonal scenario inhibits fatty acid synthesis.

Thus, the situation with increased levels of citrate and insulin, combined with decreased levels of glucagon, creates a metabolic environment conducive to fatty acid synthesis. This is why the correct answer