Nutrition regimen (4)
I believe the answer is:
diet
'nutrition regimen' 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 "Try to lose weight" , "Supposed slimming plan" , "Slimming regime" , "Legislative assembly; food regimen" , "Calorie-watching regimen" .)