Protein gel with nut spread (6)
I believe the answer is:
gluten
'protein' is the definition.
(gluten is a kind of protein)
'gel with nut spread' is the wordplay.
'with' is a charade indicator (letters next to each other).
'spread' indicates an anagram.
'gel' after 'nut' is 'nutgel'.
'nutgel' is an anagram of 'GLUTEN'.
(Other definitions for gluten that I've seen before include "Protein source" , "Gluey protein substance in wheat" , "Protein present in wheat" , "Part of wheat" , "Substance in cereal grain" .)