Meat needs oil stirred with nitrogen (4)
I believe the answer is:
loin
'meat' is the definition.
(loin is a kind of meat)
'oil stirred with nitrogen' is the wordplay.
'stirred' is an anagram indicator.
'with' means one lot of letters go next to another.
'nitrogen' becomes 'n' (N is the chemical symbol for nitrogen).
'oil' anagrammed gives 'loi'.
'loi'+'n'='LOIN'
'needs' acts as a link.
(Other definitions for loin that I've seen before include "flesh!" , "Cut of meat from between rib and haunch" , "Lumbar region" , "Beef cut" , "Either side of the backbone between the hip bone and ribs" .)