On best diet for stripping off full-body suit (6)
I believe the answer is:
onesie
'full-body suit' is the definition.
(a onesie is a one-piece garment)
'on best diet for stripping off' is the wordplay.
I cannot quite see how this works, but
'on' is found in the answer.
This explanation may well be incorrect...
(Other definitions for onesie that I've seen before include "Single-piece full body garment" , "One-piece full-body garment" .)