Calvinism imparts life (regeneration) apart from Christ and so runs afoul ofAmen! Jesus explains the sense of the entire passage in John 6 when He says, "It is the Spirit who gives life; the flesh profits nothing. The words that I speak to you are spirit, and they are life." (John 6:63) Jesus used figurative language to emphasize these great spiritual truths.
Jesus is not speaking of cannibalism here but believing in Christ unto salvation. Trusting in Him alone for salvation. Compare for example the following two verses:
John 6:47 - “Most assuredly, I say to you, he who believes in Me has everlasting life.”
John 6:58 - “He who eats this bread will live forever.”
“He who believes” in Christ is equivalent to “he who eats this bread” and the result is the same, eternal life. The parallel is also seen in verses 40 and 54:
John 6:40 - “Everyone who looks to the Son and believes in Him may have eternal life; and I will raise him up at the last day.”
John 6:54 - “Whoever eats My flesh and drinks My blood has eternal life, and I will raise him up at the last day.”
So, John 6 does not support the false doctrine of transubstantiation. On the contrary, it’s faith in Christ that is the means by which we receive the grace of God. Jesus is the Bread of Life; we eat of Him and are satisfied when we believe in Him unto salvation.
Bread represents the "staff of life." Sustenance. That which essential to sustain life. Just as bread or sustenance is necessary to maintain physical life, Jesus is all the sustenance necessary for spiritual life.
The source of physical life is blood -- "life is in the blood." As with the bread, just as blood is the empowering or source of life physically, Jesus is all the source of spiritual life necessary.
John 6:53 (NASB 2020) — 53 So Jesus said to them, “Truly, truly, I say to you, unless you eat the flesh of the Son of Man and drink His blood, you have no life in yourselves.
Ephesians 1:3 (NASB 2020) — 3 Blessed be the God and Father of our Lord Jesus Christ, who has blessed us with every spiritual blessing in the heavenly places in Christ,