Conceals guts losing a pound (6)
I believe the answer is:
belies
'conceals' is the definition.
(I've seen this before)
'guts losing a pound' is the wordplay.
'guts' becomes 'bellies'.
'losing' is a deletion indicator.
'a pound' becomes 'l'.
'bellies' with 'l' taken out is 'BELIES'.
(Other definitions for belies that I've seen before include "Contradicts" , "Shows to be quite untrue" , "Conceals" , "Disguises" .)