From Mark 7:
After he had left the crowd and entered the house, his disciples asked him about this parable. 18 “Are you so dull?” he asked. “Don’t you see that nothing that enters a person from the outside can defile them? 19 For it doesn’t go into their heart but into their stomach, and then out of the body.” (In saying this, Jesus declared all foods clean.)
20 He went on: “What comes out of a person is what defiles them. 21 For it is from within, out of a person’s heart, that evil thoughts come—sexual immorality, theft, murder, 22 adultery, greed, malice, deceit, lewdness, envy, slander, arrogance and folly. 23 All these evils come from inside and defile a person.”
(In saying this, Jesus declared all foods clean.)
In other words, God was Himself dull when he gave the laws on clean and unclean foods. Or God was dull when he told Noah to take seven pairs of clean animals and one pair of unclean animals.
v. 15 “Nothing outside a person can defile them by going into them.”
Jesus was talking about defilement, not food. Jesus said He did not come to destroy the law, the law here means the Old Testament.