"He who eats of me will hunger still, he who drinks of me will thirst for more; he who obeys me will not be put to shame, he who serves me will never fail.' All this is true of the book of Most High’s covenant, the law which Moses commanded us as an inheritance for the community of Jacob." (Sirach 24:20-22)
Just as God had provided manna to the Israelites in the desert as deliverance from starvation, so He had sent Jesus Christ into this world as a sacrificial provision to deliver us from eternal condemnation. That is the meaning of Christ being "bread from heaven."
Unlike the Torah, Christ can completely satisfy our spiritual huger and thirst (John 6:49-51). "Eating flesh" and "drinking blood" is to be understood as trusting in Christ for salvation. We consume Him by faith and He sustains us spiritually by that same means (John 6:35-40).
It is the words of Christ that impart life to those who believe (John 5:24; 6:63). This perspective of eating finds its basis in the Old Testament (Jeremiah 15:16; Ezekiel 2:8-3:3). To interpret John 6:50-58 as referring to Roman Catholic transubstantiation misses the entire point of the text.