The reference to polluted food is not to ceremonially unclean animals as listed in Leviticus 11:1–47. Rather, the reference is to animals that were ceremonially clean but nevertheless imperfect insofar as they were blind, lame, or sick. God forbade the offering of animals that were blemished or defective in any way (Leviticus 22:20; Deuteronomy 15:21; Deuteronomy 17:1). A perfect God requires perfect sacrifices.
7 By offering polluted food upon my altar. But you say, ‘How have we polluted you?’ By saying that the LORD’s table may be despised.