Improve by cutting what you eat, putting energy first (4)
I believe the answer is:
edit
'improve by cutting' is the definition.
'putting energy first' is the wordplay.
'putting' becomes 'dit' (I can't explain this - if you can you should give a lot more credence to this answer).
'energy' becomes 'e' (physics symbol as in E=mci).
'first' says to put letters next to each other.
'dit' after 'e' is 'EDIT'.
'what you eat' acts as a link.
I am not very happy about this link. Some or all of it may belong to another bit of the clue.
(Other definitions for edit that I've seen before include "Censor" , "Emend" , "Change text" , "Revise - expurgate" , "Prep for press" .)