Except that Jesus was not referring to His body in Matthew 15:17, He was explaining a parable about Kosher requirements. To presume that this one out of context verse negates His many commands to eat His body and drink His blood and His references to the bread of life is just not plausible.
Further, you have to understand the philosophical difference between accident and substance to understand the Catholic teaching on this subject. If you would like some more information I would be more than happy to help you. If not I see no reason to arm wrestle you over this.
Deuteronomy 8:3 And he humbled thee, and suffered thee to hunger, and fed thee with manna, which thou knewest not, neither did thy fathers know; that he might make thee know that man doth not live by bread only, but by every word that proceedeth out of the mouth of the LORD doth man live.
Ezek 3:1 Moreover he said unto me, Son of man, eat that thou findest; eat this scroll, and go speak unto the house of Israel. 2 So I opened my mouth, and he caused me to eat that scroll. 3 And he said unto me, Son of man, cause thy belly to eat, and fill thy bowels with this roll that I give thee. Then did I eat it; and it was in my mouth as honey for sweetness.
Jer 15:16 Thy words were found, and I did eat them; and thy word was unto me the joy and rejoicing of mine heart: for I am called by thy name, O LORD God of hosts.
Revelation 19:13 And he was clothed with a vesture dipped in blood: and his name is called The Word of God.
John 6:35 And Jesus said unto them, I am the bread of life: he that cometh to me shall never hunger; and he that believeth on me shall never thirst.
1 Corinthians 10:3 And did all eat the same spiritual meat; 4 And did all drink the same spiritual drink: for they drank of that spiritual Rock that followed them: and that Rock was Christ.
Matthew 26:26 And as they were eating, Jesus took bread, and blessed it, and brake it, and gave it to the disciples, and said, Take, eat; this is my body.
Eat and drink the word of God.