Pub diet? (5)
I believe the answer is:
local
This clue is a double definition.
'pub' is the first definition.
(one's local pub)
'diet?' is the second definition.
(lo-cal is short for 'low calories')
(Other definitions for local that I've seen before include "nearest boozer!" , "(Pub) of the district" , "Village inn" , "Restricted number" , "where the neighbours drink?" .)