Question:
A man survives 5 days without food. What is the brain's primary energy source during this prolonged fasting period?
A man survives 5 days without food. What is the brain's primary energy source during this prolonged fasting period?
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In prolonged fasting, the brain shifts from glucose dependence to using ketone bodies.
Updated On: Aug 27, 2026
- Gluconeogenesis
- Glycogenolysis
- Ketosis
- Lipolysis
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The Correct Option is C
Solution and Explanation
Concept:
During prolonged fasting, the liver produces ketone bodies from fatty acids. After a few days of fasting, the brain starts using ketone bodies as a major energy source.
Step 1: Understand early fasting.
In early fasting, glucose is supplied by glycogenolysis and gluconeogenesis.
Step 2: Understand prolonged fasting.
After several days, glycogen stores are depleted and ketone body production increases.
Step 3: Brain fuel after 5 days.
At around 5 days of starvation, the brain significantly uses: \[ \text{Ketone bodies} \]
Step 1: Understand early fasting.
In early fasting, glucose is supplied by glycogenolysis and gluconeogenesis.
Step 2: Understand prolonged fasting.
After several days, glycogen stores are depleted and ketone body production increases.
Step 3: Brain fuel after 5 days.
At around 5 days of starvation, the brain significantly uses: \[ \text{Ketone bodies} \]
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