Nutrition: protein complementation: practice question

A PSM 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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PSM · Nutrition: protein complementation

Sample item

A vegetarian family eats rice or wheat with dal at most meals. Nutrition counselling explains that this combination gives better quality protein than either food alone. Which amino acid is chiefly limiting in cereals and supplied by the pulses?

AMethionineBLysineCThreonineDTryptophan

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

The answer and the reasoning

B. Lysine

Cereal proteins are poor in lysine, whereas pulses are rich in lysine but poor in the sulphur-containing amino acids, chiefly methionine. Combining the two supplements each other's deficit and raises the biological value of the mixed protein. Maize is notably limited in tryptophan as well.

Option by option

A. Methionine
Methionine is the limiting amino acid in pulses, and cereals supply it.
B. Lysine (correct)
Correct. Lysine is the first limiting amino acid in cereals and is abundant in pulses.
C. Threonine
Threonine is a second limiting amino acid in some cereals, but lysine is limiting first.
D. Tryptophan
Tryptophan is limiting in maize, but lysine is the chief shortfall in cereals generally.

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 PSM question

What is the answer to this PSM question?

The best answer is B, Lysine. Cereal proteins are poor in lysine, whereas pulses are rich in lysine but poor in the sulphur-containing amino acids, chiefly methionine.

Why is "Methionine" not the answer?

Methionine is the limiting amino acid in pulses, and cereals supply it.

Why is "Threonine" not the answer?

Threonine is a second limiting amino acid in some cereals, but lysine is limiting first.

Why is "Tryptophan" not the answer?

Tryptophan is limiting in maize, but lysine is the chief shortfall in cereals generally.

What concept does this question test?

It tests Nutrition: protein complementation in PSM. Combining the two supplements each other's deficit and raises the biological value of the mixed protein. Maize is notably limited in tryptophan as well.

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 Nutrition: protein complementation?

Practise biostatistics with small calculations until sensitivity, predictive values and risk measures are automatic. Then use the flashcards and the other PSM 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.