Regimen upset when eating universal sweet food item (8)
I believe the answer is:
meringue
'sweet food item' is the definition.
Although both the answer and definition are singular nouns, I can't understand how they can define each other.
'regimen upset when eating universal' is the wordplay.
'upset' is an anagram indicator.
'when eating' indicates putting letters inside.
'universal' becomes 'u'.
'regimen' is an anagram of 'meringe'.
'meringe' enclosing 'u' is 'MERINGUE'.
Can you help me to learn more?
(Other definitions for meringue that I've seen before include "Light cake of eggs & sugar" , "Egg-based treat" , "Egg white/sugar cake" , "Cake made mostly of sugar" , "Dessert of beaten egg-white and sugar, baked crisp" .)