General physiology: body water in obesity: 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 · General physiology: body water in obesity

Sample item

Two men weigh the same, but one is lean and the other markedly obese. Compared with the lean man, the obese man will have which finding on total body water measurement?

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

The answer and the reasoning

A. A lower total body water as a percentage of body weight

Adipose tissue contains little water, so a person with more fat has a lower proportion of body weight as water. Lean tissue is about three quarters water. This also explains why women and older people, who carry relatively more fat, have a lower water percentage.

Option by option

  • A. A lower total body water as a percentage of body weight (correct)

    Correct. Fat holds little water, so the water fraction of body weight falls.

  • B. A higher total body water as a percentage of body weight

    A higher fraction would apply to a lean person, as lean tissue is water-rich.

  • C. A larger intracellular share of body water per kilogram

    Fat cells do not enlarge the intracellular water share per kilogram of body weight.

  • D. The same percentage, since water content is fixed

    Water fraction varies with body composition and is not fixed.

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.

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Questions about this Physiology question

What is the answer to this Physiology question?

The best answer is A, A lower total body water as a percentage of body weight. Adipose tissue contains little water, so a person with more fat has a lower proportion of body weight as water.

Why is "A higher total body water as a percentage of body weight" not the answer?

A higher fraction would apply to a lean person, as lean tissue is water-rich.

Why is "A larger intracellular share of body water per kilogram" not the answer?

Fat cells do not enlarge the intracellular water share per kilogram of body weight.

Why is "The same percentage, since water content is fixed" not the answer?

Water fraction varies with body composition and is not fixed.

What concept does this question test?

It tests General physiology: body water in obesity in Physiology. Lean tissue is about three quarters water. This also explains why women and older people, who carry relatively more fat, have a lower water percentage.

How hard is this question?

We tag it as an application question: it asks you to use a fact on a patient or a finding. 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 General physiology: body water in obesity?

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.