Food picked up with reduced fat -- it's criminal! (7)
I believe the answer is:
burglar
'it's criminal' is the definition.
(burglar is a kind of criminal)
'food picked up with reduced fat' is the wordplay.
'food' becomes 'grub' (grub can informally mean food).
'picked up' is a reversal indicator.
'with' means one lot of letters go next to another.
'reduced' means to remove the last letter.
'fat' becomes 'lard' (lard is a kind of fat).
'grub' reversed gives 'burg'.
'lard' with its last letter taken away is 'lar'.
'burg'+'lar'='BURGLAR'
(Other definitions for burglar that I've seen before include "Housebreaker" , "Thief (entering building)" , "He takes" , "Intruder with intent to steal" , "House-violating thief" .)