Upset: halving diet given emphasis (10)
I believe the answer is:
distressed
'upset' is the definition.
(I know that upset can be written as distressed)
'halving diet given emphasis' is the wordplay.
'halving diet' becomes 'died' (I can't justify this - if you can you should believe this answer much more).
'given' is an insertion indicator.
'emphasis' becomes 'stress' (synonyms).
'died' going around 'stress' is 'DISTRESSED'.
Can you help me to learn more?
(Other definitions for distressed that I've seen before include "like Samson when deprived of his strength?" , "Upset; deliberately aged" , "in anguish?" , "In deep pain or sorrow" , "Anxious" .)