Food is for pleasure, mostly (4)
I believe the answer is:
tofu
'food' is the definition.
(tofu is a kind of food)
'for pleasure mostly' is the wordplay.
'for' becomes 'to' (eg both can mean 'in the opinion of').
'pleasure' becomes 'fun' (I've seen this before).
'mostly' means to remove the last letter.
'fun' with its last letter taken off is 'fu'.
'to'+'fu'='TOFU'
'is' is the link.
(Other definitions for tofu that I've seen before include "nosh for vegetarians" , "Curdled soybean dish" , "Food from bean curd" , "Unfermented soya bean curd" , "Vegetarian foodstuff made from soya beans" .)