Will such foods make you prim? (7)

I believe the answer is:

starchy

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'prim?' is the definition.
Both the definition and answer are adjectives. Perhaps there's a link between them I don't understand?

I cannot understand how the rest of the clue works.

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(Other definitions for starchy that I've seen before include "Stiff, like potatoes" , "Stiff and formalistic" , "Unbending" , "Conventional" , "Stiff, formal" .)

I've seen this clue in the Evening Standard.

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