Unwanted body fat (4)
I believe the answer is:
flab
'unwanted body fat' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for flab that I've seen before include "Loose body fat" , "Excess body fat" , "Excess fat (colloq.)" , "Loose flesh; fat" , "Sign of over-indulgence" .)