**Question:** Ketone body is not utilised by -

A. Liver
B. Brain
C. Kidney
D. Muscle

**Core Concept:** Ketone bodies are formed during periods of high fatty acid oxidation, such as in fasting or starvation, and are used as an alternative energy source when glucose is scarce. Ketone bodies include beta-hydroxybutyrate, acetoacetate, and acetone.

**Why the Correct Answer is Right:** Ketone bodies are primarily utilized by peripheral tissues, particularly in muscle, for energy production. However, they are not the primary energy source for organs with high energy demands like the brain. This is because the brain has a high demand for glucose, which is not efficiently converted to ketone bodies.

**Why Each Wrong Option is Incorrect:**

A. Liver: While liver plays a role in ketone body production, it does utilize glucose for energy rather than ketone bodies.
B. Brain: As mentioned before, the brain mainly relies on glucose for energy, not ketone bodies.
C. Kidney: Kidneys can utilize ketone bodies, but the focus is on glucose as the primary energy source.
D. Muscle: Muscle does utilize ketone bodies, but the correct answer is chosen because of the brain's preference for glucose.

**Clinical Pearl / High-Yield Fact:** In situations where glucose is unavailable or insufficient, such as in diabetic ketoacidosis (DKA), ketone bodies can accumulate in the blood, leading to ketosis and ketoacidosis. This can be detrimental to the brain, as ketone bodies are not its preferred energy source.

**Correct Answer:** B. Brain