Food is turning, affected internally (6)
I believe the answer is:
scampi
'food' is the definition.
(scampi is a kind of food)
'is turning affected internally' is the wordplay.
'turning' indicates anagramming the letters.
'affected' becomes 'camp' (I've seen this before).
'internally' means one lot of letters goes inside another.
'is' anagrammed gives 'si'.
'si' placed around 'camp' is 'SCAMPI'.
(Other definitions for scampi that I've seen before include "Breaded prawns" , "Cooked Norway lobster" , "Edible crustaceans" , "Type of seafood" , "Cooked Norway lobsters" .)