Linked to diet change (4)
I believe the answer is:
tied
'linked' is the definition.
(tying is a kind of linking)
'diet change' is the wordplay.
'change' indicates anagramming the letters.
'diet' anagrammed gives 'TIED'.
'to' is the link.
(Other definitions for tied that I've seen before include "Bound to diet" , "Fastened, bound" , "Made into a knot" , "In no-win situation" , "Linked; restricted" .)