Contemplate a change in meat diet (8)
I believe the answer is:
meditate
'contemplate' is the definition.
(I know that contemplate can be written as meditate)
'a change in meat diet' is the wordplay.
'a change in' is an anagram indicator.
'meat'+'diet'='meatdiet'
'meatdiet' anagrammed gives 'MEDITATE'.
(Other definitions for meditate that I've seen before include "Spend time in thought" , "Think intently and at length" , "Ponder" , "Think deeply and quietly" , "Think contemplatively" .)