Large body to go comfortably round, being out of shape (5)
I believe the answer is:
unfit
'out of shape' is the definition.
(out of shape can mean unfit or unhealthy)
'large body to go comfortably round' is the wordplay.
'large body' becomes 'UN' (United Nations, large international body).
'to go comfortably round' becomes 'fit' (as in clothing fitting round someone).
'un'+'fit'='UNFIT'
'being' is the link.
(Other definitions for unfit that I've seen before include "Inappropriate" , "Not in good physical condition, or not suitable" , "Unsuitable" , "Inapt" , "Ill-suited" .)