Bound with poor diet (4)
I believe the answer is:
tied
'bound' is the definition.
('tie' can be a synonym of 'bind')
'poor diet' is the wordplay.
'poor' indicates an anagram.
'diet' is an anagram of 'TIED'.
'with' acts as a link.
(Other definitions for tied that I've seen before include "Bound; placed equal" , "Restricted, bound" , "eg Scored 1-1" , "United" , "In no-win situation" .)