The early church considered the change from bread & wine to body&blood to be a mystery and didn't try to define it.
Transubstantiation is a very specific definition that comes from the Roman church and does not appear until the 1100s. Since we cannot discuss Roman Catholic doctrine in this particular thread, I suggest that you google it to get a better understanding.
The ancient church simply accepted what they received from the apostles and didn't ask how God does what He does.
I see no reason not to accept it at face value.
There is nothing in John 6 to suggest that what Jesus was presenting wans to be entirely understood as a parable or a metaphor or that it was "symbolic". (Which is code for, "I'm not believing that.") He did not explain what He meant to the disciples at a later time as He did with the parable of the sower (Luke 8:11-15) or the teaching on what defiles a person. (Mar 7:19-23)
My personal analysis/breakdown of the passage is as follows: (RSV)
THE BREAD OF LIFE – the metaphor
John 6:48(1) "I am the bread of life. He who comes to me will never go hungry, and he who believes in me will never be thirsty.
(2) I am the bread of life.
49 Your forefathers ate the manna in the desert, yet they died.
50(3) But here is the bread that comes down from heaven, which a man may eat and not die.
51(4) I am the living bread that came down from heaven.
(5) If anyone eats of this bread, he will live forever.
THE BREAD IS MY FLESH – the metaphor explained
(6) This bread is my flesh, which I will give for the life of the world."
53 Jesus said to them, "I tell you the truth,
(7) unless you eat the flesh of the Son of Man and drink his blood, you have no life in you.
54(8) Whoever eats my flesh and drinks my blood has eternal life, and I will raise him up at the last day.
55 (9) For my flesh is real food and my blood is real drink.
56(10) Whoever eats my flesh and drinks my blood remains in me, and I in him. (See John 15.)
57 Just as the living Father sent me and I live because of the Father, so
(11) the one who feeds on me will live because of me.
THE BREAD OF LIFE – the lesson summarized
58(12) This is the bread that came down from heaven. Your forefathers ate manna and died, but
(13) he who feeds on this bread will live forever."
I note that Peter's response to Jesus' question as to whether the disciples would also leave Him, because the teaching was hard, was, "Lord, to whom shall we go? thou hast the words of eternal life. And we believe and are sure that thou art that Christ, the Son of the living God." (John 6:68-69) Peter gave no indication that he understood.
my 2 kopecks
iakov the fool