Q: can a person use milk to shave legs? Would this be wasting?
A: Respectable items such as food should not be used for degrading functions without a valid reason. It is opposed to the rules of ‘adab (respect) for food. For medical purposes and other legitimate reasons, one would be allowed to use it.
When other products do exist to fulfill this task, it would be a sin to use something that others can use as part of their survival. To use halaal foods directly would be a corruptible measure and would function against ayaat that stress upon the importance of eating pure and being grateful and not using food as part of wastage.
Allah Certainly Knows Best.