Spot sweetheart on American diet? (6)
I believe the answer is:
locale
'spot' is the definition.
(spot can mean a location)
'sweetheart on american diet?' is the wordplay.
'sweetheart' becomes 'e' (the heart/centre of 'sweet').
'on' means one lot of letters go next to another.
'american diet?' becomes 'local' (low calories).
'e' put after 'local' is 'LOCALE'.
(Other definitions for locale that I've seen before include "Scene of event or occurrence" , "Setting" , "Venue" , "Spot" , "Place associated with particular events" .)