Too much eaten outside — some people can't take it (6)
I believe the answer is:
gluten
'some people can't take it' is the definition.
(some people have gluten intolerance)
'too much eaten outside' is the wordplay.
'too much' becomes 'glut' (I've seen this before).
'outside' says to hollow out the word (remove centre letters).
'eaten' with its middle removed is 'en'.
'glut'+'en'='GLUTEN'
(Other definitions for gluten that I've seen before include "Protein in wheat grains" , "Substance in cereal grain" , "Protein in grain that gives cohesiveness to dough" , "Protein left after starch is removed from cereal grains" , "Part of wheat" .)