Sober user ate bananas (7)
I believe the answer is:
austere
'sober' is the definition.
(I've seen this in another clue)
'user ate bananas' is the wordplay.
'bananas' is an anagram indicator (informal term for mad).
'user'+'ate'='userate'
'userate' anagrammed gives 'AUSTERE'.
(Other definitions for austere that I've seen before include "Lacking adornments" , "Sure eat up and become without luxury" , "Bleak" , "Stern or very plain" , "Lacking comforts; strict" .)