Secured change of diet (4)
I believe the answer is:
tied
'secured' is the definition.
(tying is a kind of securing)
'change of diet' is the wordplay.
'change of' indicates anagramming the letters.
'diet' with letters rearranged gives 'TIED'.
(Other definitions for tied that I've seen before include "Bonded" , "Drawn" , "With an equal score" , "Linked; restricted" , "eg Scored 1-1" .)