Try to lighten up? (4)
I believe the answer is:
diet
'try to lighten up?' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for diet that I've seen before include "cut down" , "Special food regime" , "food one eats on a regular basis" , "A disciplined food regime" , "Restricted cheer" .)