Someone who exists for food (5)
I believe the answer is:
liver
This could be a double definition.
'someone who exists' is the first definition.
'liver' can be an answer for 'someone' (liver is a kind of someone). I am not certain of the rest of the definition.
'for food' is the second definition.
(liver is a kind of food)
Can you help me to learn more?
(Other definitions for liver that I've seen before include "Bile-secreting gland" , "Large organ of body" , "Large gland" , "Human organ" , "Glandular organ in the abdomen" .)