One stealing food sent back with reduced fat (7)
I believe the answer is:
burglar
'one stealing' is the definition.
(burglars steal)
'food sent back with reduced fat' is the wordplay.
'food' becomes 'grub' (grub is a kind of food).
'sent back' is a reversal indicator.
'with' says to put letters next to each other.
'reduced' means to remove the last letter.
'fat' becomes 'lard' (lard is a kind of fat).
'grub' written backwards gives 'burg'.
'lard' with its last letter taken away is 'lar'.
'burg'+'lar'='BURGLAR'
(Other definitions for burglar that I've seen before include "One enters a building in order to steal" , "Thief (entering building)" , "Breaker and enterer?" , "House-violating thief" , "Housebreaker" .)