Smelly new diet at the welfare centre (5)
I believe the answer is:
fetid
'smelly' is the definition.
(fetid can mean smelly or odorous)
'new diet at the welfare centre' is the wordplay.
'new' indicates an anagram.
'at' means one lot of letters go next to another (I've seen this in other clues).
'centre' says to take the centre.
The middle of 'welfare' is 'f'.
'diet' with letters rearranged gives 'etid'.
'etid' put after 'f' is 'FETID'.
(Other definitions for fetid that I've seen before include "Smelling bad, stinking" , "Malodorous, stinking" , "Putrid and stinking" , "Stinking, rank" , "Stinking, perhaps breath" .)