Count calories (4)
I believe the answer is:
diet
'count calories' 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 "See 19" , "(Perhaps, try to) reduce rump; parliament" , "Regime followed by slimmer" , "Range of food eaten" , "Regimen for eating" .)