After 1-2 weeks of starvation, which organ adapts to use ketones as an energy source?

• A. Brain
• B. Liver
• C. Adipose tissue
• D. Skeletal muscle

Answer: (A)

During prolonged fasting, the brain shifts to using ketone bodies for energy, which helps spare glucose for other tissues. After about 1–2 weeks without food, ketones produced by the liver from fatty acids become a major fuel for the brain. This adaptation reduces the brain’s demand for glucose and helps preserve muscle protein for gluconeogenesis elsewhere in the body. The liver, while responsible for making ketones, does not use them for its own energy, and adipose tissue mainly supplies fatty acids rather than ketones. So the organ adapting to use ketones as a primary energy source is the brain.