Bound to have a change of diet (4)
I believe the answer is:
tied
'bound' is the definition.
('tie' can be a synonym of 'bind')
'a change of diet' is the wordplay.
'a change of' indicates an anagram (the letter order is changed).
'diet' with letters rearranged gives 'TIED'.
'to have' is the link.
(Other definitions for tied that I've seen before include "Bound; placed equal" , "have equal scores" , "Drew; bound" , "(Of pub) owned and run by a brewery" , "Linked; restricted" .)