Fancy a limit on food? (7)
I believe the answer is:
caprice
'fancy' is the definition.
(thesaurus)
'a limit on food?' is the wordplay.
'a limit' becomes 'cap' (I've seen this before).
'on' means one lot of letters go next to another.
'food?' becomes 'rice' (rice is a kind of food**).
'cap'+'rice'='CAPRICE'
(Other definitions for caprice that I've seen before include "Sudden change of mind" , "'Impulse, whim (7)'" , "Sudden impulse" , "A whim or piece of fancy" , "Whimsy" .)