Best English, low in calories (5)
I believe the answer is:
elite
'best' is the definition.
(elite can mean the very best of a group)
'english low in calories' is the wordplay.
'english' becomes 'E' (abbreviation as in OED).
'low in calories' becomes 'lite' (light in calories, calorie-lite).
'e'+'lite'='ELITE'
(Other definitions for elite that I've seen before include "Aristocratic" , "Select body, cream" , "Chosen ones" , "Choice; best" , "Letter size; superior group" .)