It's unpleasant to eat crusts of rye loaf (5)
I believe the answer is:
bread
'loaf' is the definition.
(I've seen this before)
'it's unpleasant to eat crusts of rye' is the wordplay.
'it's unpleasant' becomes 'bad'.
'to eat' means one lot of letters goes inside another.
'crusts of rye' becomes 're' (I can't explain this - if you can you should give a lot more credence to this answer).
'bad' going around 're' is 'BREAD'.
Can you help me to learn more?
(Other definitions for bread that I've seen before include "It may be made from meal" , "Lolly - basic food" , "Dosh (slang)" , "Staple diet" , "Gracefully thin" .)