Go on reduced fare (4)
I believe the answer is:
diet
'fare' is the definition.
(fare can mean food)
'go on reduced' is the wordplay.
'go' becomes 'die' (synonyms).
'on' becomes 'at' (I've seen this in other clues).
'reduced' means to remove the first letter.
'at' with its first letter removed is 't'.
'die'+'t'='DIET'
(Other definitions for diet that I've seen before include "Calorie-watching regimen" , "Food - parliament" , "Legislative assembly in some countries" , "Food intake regime" , "Try to lose weight" .)