Organs that can utilise energy formed in ketogenesis are

The correct answer is All of the above.

Ketogenesis is the biochemical process by which the liver produces ketone bodies (acetoacetate, β-hydroxybutyrate, and acetone) from acetyl-CoA, primarily during periods of starvation, fasting, low-carbohydrate diets, or prolonged intense exercise.

While the liver is the primary site of ketogenesis, it lacks the enzyme β-ketoacyl-CoA transferase (thiophorase), which is essential for activating ketone bodies. Therefore, the liver cannot utilize the ketone bodies it produces. Instead, these ketone bodies are released into the bloodstream to be used as an alternative energy source by various extrahepatic (outside the liver) organs and tissues. Let's look at the organs listed in the options:

1. Brain: Under normal conditions, the brain relies almost exclusively on glucose for energy. However, during periods of prolonged fasting or starvation, the brain adapts to utilize ketone bodies (specifically acetoacetate and β-hydroxybutyrate) as its primary energy source, meeting up to 60-75% of its energy needs.

2. Skeletal muscle: Skeletal muscles readily utilize ketone bodies for energy, especially during the early stages of fasting or during prolonged aerobic exercise, sparing glucose for glucose-dependent tissues.

3. Heart: The cardiac muscle (heart) is metabolically highly flexible and constantly active. It prefers fatty acids but can efficiently utilize ketone bodies, glucose, and lactate to meet its high energy demands. In fact, ketone bodies are a highly efficient fuel source for the heart.

Since the brain, skeletal muscle, and heart can all utilize the energy formed during ketogenesis, the correct option is "All of the above".