Reduced fare when tide turns (4)
I believe the answer is:
diet
'reduced fare' is the definition.
(I've seen this in another clue)
'tide turns' is the wordplay.
'turns' indicates anagramming the letters.
'tide' is an anagram of 'DIET'.
'when' is the link.
(Other definitions for diet that I've seen before include "Choice of food" , "control weight" , "Health food - Council" , "International conference" , "See 19" .)