Something to do with the fat (4)
I believe the answer is:
chew
'fat' is the definition.
The answer and definition can be both related to consumption as well as being verbs in their base form.
Perhaps you can see a link between them that I don't see?
'something to do with' is the wordplay.
'something to do' becomes 'che' (I can't explain this - if you can you should believe this answer much more).
'with' becomes 'w' (abbreviation).
'che'+'w'='CHEW'
'the' acts as a link.
Can you help me to learn more?
(Other definitions for chew that I've seen before include "champ" , "Gnaw" , "bit of tobacco" , "Treat for dog" , "Reflect on" .)