Following a meal, he is responsible for someone's health! (11)
I believe the answer is:
toastmaster
'following a meal he is responsible' is the definition.
The answer is a person as well as being a singular noun. This is suggested by the definition.
'someone's health' is the wordplay.
I cannot quite see how this works, but
'health' could be 'toast' (I've seen this before) and 'toast' is found in the answer.
'someone' could be 'master' (master is a kind of someone) and 'master' is found within the answer.
No letters remain.
This explanation may well be incorrect...
'for' acts as a link.
Can you help me to learn more?
(Other definitions for toastmaster that I've seen before include "Official at formal dinner" , "Official at social event" , "Master of ceremonies at a banquet" , "Address given after my introduction" , "One introducing" .)