Plausible food contains nut (7)
I believe the answer is:
tenable
'plausible' is the definition.
(thesaurus)
'food contains nut' is the wordplay.
'food' becomes 'table' (table is a kind of food).
'contains' is an insertion indicator.
'nut' becomes 'en' ('nut' is printers' slang for an en space).
'table' enclosing 'en' is 'TENABLE'.
(Other definitions for tenable that I've seen before include "Can be maintained" , "Able to be believed" , "Believable" , "Able to be held" , "Able to be defended against attack or objection" .)