Nothing in belly brings complaint (4)
I believe the answer is:
gout
'complaint' is the definition.
(gout is a kind of health problem)
'nothing in belly' is the wordplay.
'nothing' becomes 'O' (O resembles 0).
'in' means one lot of letters goes inside another.
'belly' becomes 'gut' (informal term for the stomach or gut).
'o' inserted into 'gut' is 'GOUT'.
'brings' is the link.
(Other definitions for gout that I've seen before include "Painful inflammation of the foot" , "Toe-swelling disease" , "Toe-inflammation disease" , "Disease causing inflammation of toes and feet" , "Disease causing pain in joints" .)