Nail in food (4)
I believe the answer is:
tack
This clue is a double definition.
'nail' is the first definition.
(I know that tack is a type of tack)
'food' is the second definition.
(I've seen this before)
'in' is the link.
(Other definitions for tack that I've seen before include "Small broad-headed nail" , "fix > riding gear" , "Rubbishy things" , "Small nail; sail (boat) against the wind" , "Turn and sail into the wind" .)