Fed a sugar-free preventative (9)

I believe the answer is:

safeguard

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

'preventative' is the definition.
Although both the answer and definition are singular nouns, I cannot see how one could define the other.

'fed a sugar-free' is the wordplay.
'free' is an anagram indicator.
'fed'+'a'+'sugar'='fedasugar'
'fedasugar' anagrammed gives 'SAFEGUARD'.

Can you help me to learn more?

(Other definitions for safeguard that I've seen before include "Preserve" , "Protect" , "Protective measure" .)

I've seen this clue in the Sydney Morning Herald.

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