Break down (in the stomach) (6)
I believe the answer is:
digest
'break down in the stomach' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for digest that I've seen before include "Periodical that summarizes the news" , "Long walk, itinerant person" , "publication" , "Think over, absorb into the mind" , "Absorb and assimilate, like food" .)