Variable food leader spat out? That's disgusting (4)
I believe the answer is:
yuck
'that's disgusting' is the definition.
(expression of disgust)
'variable food leader spat out?' is the wordplay.
'variable' becomes 'y' (algebra).
'food' becomes 'tuck' (tuck can mean food).
'leader spat out?' means to remove the first letter.
'tuck' with its first letter taken away is 'uck'.
'y'+'uck'='YUCK'
(Other definitions for yuck that I've seen before include "Ugh!" , "Disgusting (interj.)" , "Expression of disgust; rhymes with male deer" , "That's disgusting!" , "Exclamation of disgust" .)