AAMC FL Practice Exam

What occurs as a result of fatty acid oxidation during fasting?

1. Decrease in glucose levels

2. Production of ketone bodies

3. Enhancement of protein synthesis

4. Increase in fat storage

The correct answer is: Production of ketone bodies

During fasting, the body undergoes several metabolic changes to maintain energy homeostasis, and fatty acid oxidation plays a key role in this process. When glucose availability is low due to a lack of food intake, the body shifts its energy production from glucose to fatty acids. Fatty acid oxidation occurs primarily in the liver and leads to the breakdown of stored triglycerides into free fatty acids, which then enter the mitochondria for beta-oxidation. One of the significant products of this process is ketone bodies. As fatty acids are oxidized, they generate acetyl-CoA, which in excess can be converted into ketone bodies—specifically acetoacetate, beta-hydroxybutyrate, and acetone. These ketone bodies serve as an alternative energy source for tissues such as the brain and muscles during prolonged fasting when glucose is scarce. This metabolic adaptation allows the body to utilize fat stores effectively, preventing muscle breakdown for energy and providing a continuous fuel supply. Thus, the production of ketone bodies is a crucial outcome of fatty acid oxidation during fasting, reflecting the body's shift towards using fat as its primary fuel source in the absence of dietary carbohydrates.