Metabolism: starvation: practice question

A Physiology question in the style of the NEET PG paper. Answer it first, then read why the right option is right and why each of the others is wrong.

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Physiology · Metabolism: starvation

Sample item

A person who has fasted for three weeks shows a fall in daily urinary nitrogen loss compared with the first days of fasting. Which adaptation explains this?

AMuscle protein breakdown increases to meet brain glucose needsBThe liver switches off ketogenesis to conserve fatCRed blood cells begin to use ketone bodiesDThe brain uses ketone bodies for much of its energy, reducing glucose demand and protein breakdown

Original practice item, not a recalled exam question. Nothing here is recorded.

The answer and the reasoning

D. The brain uses ketone bodies for much of its energy, reducing glucose demand and protein breakdown

In early fasting the body relies on glycogen and then on gluconeogenesis from amino acids. As fasting continues, hepatic ketone production rises and the brain adapts to use ketone bodies, so less glucose is needed. Gluconeogenesis, and so protein breakdown and urea formation, decline, preserving muscle mass.

Option by option

A. Muscle protein breakdown increases to meet brain glucose needs
Protein breakdown is greatest in early fasting and falls later.
B. The liver switches off ketogenesis to conserve fat
Ketogenesis is stimulated, not switched off, by low insulin and high glucagon.
C. Red blood cells begin to use ketone bodies
Red cells lack mitochondria and depend on glucose throughout fasting.
D. The brain uses ketone bodies for much of its energy, reducing glucose demand and protein breakdown (correct)
Correct. Ketone use by the brain spares body protein.

Source note: Original NextPrep sample item — pending expert review. This item is original practice material awaiting independent expert review, so confirm important facts in a standard textbook.

Questions about this Physiology question

What is the answer to this Physiology question?

The best answer is D, The brain uses ketone bodies for much of its energy, reducing glucose demand and protein breakdown. In early fasting the body relies on glycogen and then on gluconeogenesis from amino acids.

Why is "Muscle protein breakdown increases to meet brain glucose needs" not the answer?

Protein breakdown is greatest in early fasting and falls later.

Why is "The liver switches off ketogenesis to conserve fat" not the answer?

Ketogenesis is stimulated, not switched off, by low insulin and high glucagon.

Why is "Red blood cells begin to use ketone bodies" not the answer?

Red cells lack mitochondria and depend on glucose throughout fasting.

What concept does this question test?

It tests Metabolism: starvation in Physiology. As fasting continues, hepatic ketone production rises and the brain adapts to use ketone bodies, so less glucose is needed. Gluconeogenesis, and so protein breakdown and urea formation, decline, preserving muscle mass.

How hard is this question?

We tag it as a multi-step question: it asks you to combine more than one idea. The tag is our own editorial judgement, not an official difficulty rating, so read the reason for every option, not only the answer.

How should I study Metabolism: starvation?

For each system, sketch the key graph (pressure–volume loop, oxygen dissociation curve, nephron handling) and explain it aloud. Then use the flashcards and the other Physiology questions on this site to test what stuck.

Is this a real NEET PG question?

No. It is an original practice item (editorial status: sample, version 1). NextPrep does not publish recalled or leaked questions, and independent faculty review of this item has not been completed yet, so confirm important facts in a standard textbook.