Unfortunately, turned a number against food (5)
I believe the answer is:
salad
'food' is the definition.
(salad is a kind of food)
'unfortunately turned a number against' is the wordplay.
'unfortunately' becomes 'alas' (I've seen this before).
'turned' says the letters should be written in reverse.
'a number' becomes 'd' (D is an example**).
'against' says to put letters next to each other.
'alas' back-to-front is 'sala'.
'sala'+'d'='SALAD'
(Other definitions for salad that I've seen before include "one gets dressed" , "Healthy dish" , "One that may be dressed for dinner" , "One may well be green" , "Cold dish of veg and herbs" .)