During fasting, which statement about ketone bodies is true?

During fasting, which statement about ketone bodies is true?

• A. They provide brain energy and minimize gluconeogenesis and protein breakdown
• B. They increase protein synthesis
• C. They are used to store glucose
• D. They have no role in brain metabolism

Answer: (A)

Ketone bodies act as an alternative brain fuel during fasting. When glucose becomes scarce, the liver converts fatty acids into ketones (acetoacetate and beta-hydroxybutyrate), which cross into the brain and supply a substantial portion of its energy needs. This shift reduces the brain’s demand for glucose, which in turn lowers hepatic gluconeogenesis from amino acids and helps spare body protein from breakdown. In other words, ketones provide energy for the brain and, by meeting that energy demand, lessen the need to break down protein for glucose production. They are not a storage form of glucose, they don’t directly increase protein synthesis, and they do play a meaningful role in brain metabolism during fasting.

Ketone bodies act as an alternative brain fuel during fasting. When glucose becomes scarce, the liver converts fatty acids into ketones (acetoacetate and beta-hydroxybutyrate), which cross into the brain and supply a substantial portion of its energy needs. This shift reduces the brain’s demand for glucose, which in turn lowers hepatic gluconeogenesis from amino acids and helps spare body protein from breakdown. In other words, ketones provide energy for the brain and, by meeting that energy demand, lessen the need to break down protein for glucose production. They are not a storage form of glucose, they don’t directly increase protein synthesis, and they do play a meaningful role in brain metabolism during fasting.