Crossword Genius

A writer's tip for something good in diet (5)

Ross

I believe the answer is:

fibre

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

'diet' is the definition.
Although both the answer and definition are singular nouns, I can't understand how one could define the other.

'a writer's tip for something good in' is the wordplay.
'a writer' becomes 'I' (the person who is writing these clues).
'tip' says to take the initial letters (I've seen 'tip of' mean this).
'something good' becomes 'bre' (I can't justify this - if you can you should believe this answer much more).
'in' is an insertion indicator.
The initial letter of 'for' is 'f'.
'f'+'bre'='fbre'
'i' inserted into 'fbre' is 'FIBRE'.

Can you help me to learn more?

(Other definitions for fibre that I've seen before include "In brief, a thread" , "Thread, filament" , "Texture - strength of character" , "Thread - strength of character" , "Coarse plant food, low in nutrients" .)

I've seen this clue in the Evening Standard.
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