Live healthy, following start of diet (5)
I believe the answer is:
dwell
'live' is the definition.
(to live/dwell somewhere)
'healthy following start of diet' is the wordplay.
'healthy' becomes 'well' (associated in meaning).
'following' means one lot of letters go next to another.
'start of' indicates taking the first letters.
The first letter of 'diet' is 'd'.
'well' put after 'd' is 'DWELL'.
(Other definitions for dwell that I've seen before include "Think moodily (on something)" , "Reside - linger" , "Live (in a place)" , "Hang out" , "Harp" .)