Crossword Genius

An element of helpfulness in diet (4)

Ross

I believe the answer is:

iron

I'm a little stuck... Click here to teach me more about this clue!

This could be a double definition.

'an element' is the first definition.
(iron is a kind of element)

'helpfulness in diet' is the second definition.
Both the definition and answer are adjectives. Perhaps they are linked in a way I don't understand?

'of' is the link.

Can you help me to learn more?

(Other definitions for iron that I've seen before include "Hard metal" , "Smooth - driver?" , "Metallic element, symbol Fe" , "Metal - press" , "sports club" .)

I've seen this clue in the Evening Standard.
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