Jesus is the Bread of Life and just as bread nourishes our physical bodies, Jesus gives and sustains eternal life to all believers. John 6:35- "I am the bread of life. He who comes to Me shall never hunger, and he who believes in Me shall never thirst." Jesus uses figurative language to emphasize these spiritual truths. Jesus explains the sense of the entire passage when He says in John 6:63 - "It is the Spirit who gives life; the flesh profits nothing. The words that I speak to you are spirit, and they are life."
The literal interpretation of eating flesh and drinking blood (cannibalism) is absurd. By faith we partake of Christ, and the benefits of His bodily sacrifice on the cross and shed blood, receiving eternal life. Eating and drinking here is not about cannibalism, but the reception of God’s grace by believing in Christ unto salvation, as He makes clear in metaphoric and plain language:
John 6:40 - Everyone who looks to the Son and believes in Him may have everlasting 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.
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 drinks My blood" as we see the result is the same, eternal life.
John 6 does not afford any support to the Roman Catholic doctrine of transubstantiation. 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.