It's natural in food we hear (6)
I believe the answer is:
Here is my best explanation:
'it's natural' is the definition.
('inbred' can be similar in meaning to 'natural')
'in food we hear' is the wordplay.
'food' becomes 'bread' (bread is a kind of food).
'we hear' indicates a 'sounds like' (homophone) clue.
'bread' sounds like 'bred'.
(Other definitions for inbred that I've seen before include "too much Montague blood?", "Deep-seated", "From too-closely-related family", "It's natural", "Was deep in thought", "Congenital - unwisely inter-related", "from a restricted gene pool?", "Innate", "4 across" and "Inborn".)