Lose weight within judicious limits (4)
I believe the answer is:
slim
'lose weight' is the definition.
('slim' can be a synonym of 'lose weight')
'within judicious limits' is the wordplay.
'within' says the answer is hidden in the clue.
'SLIM' can be found hidden inside 'judicious limits'.
(Other definitions for slim that I've seen before include "Gracefully thin" , "to make one lose weight" , "Very small; WW2 Burma commander" , "Slender or slight" , "Take off weight as by dieting" .)