The most common and most likely answer to this crossword clue is the 6 letter word GLUTEN
I've seen this crossword clue in The Guardian
G
L
U
T
E
N
More clues leading to the result GLUTEN
- Something in wheat needs good clay with nitrogen
- Protein excess ends in muscle expansion
- Too much eaten outside — some people can’t take it
- Finish wiping bottom after an excess in sticky substance
- Wheat protein in full supply, odd bits removed from beans
- Protein surplus approaching European margins
- Gut feeling regularly affected by this
- Excess of European intervention finally in protein
- Instrument cutting grain husks, finding substance in wheat
- Part of wheat surplus sent away from borders
Buddy explains!

The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does GLUTEN mean?
GLUTEN noun- Fibrin (formerly considered as one of the "animal humours").
- Any gluey, sticky substance.
- The major protein in cereal grains, especially wheat; responsible for the elasticity in dough and the structure in baked bread.
- A gluey, sticky mass of clay, bitumen etc.