I am the living bread which came down from heaven; if any one eats of this bread, he will live for ever; and the bread which I shall give for the life of the world is my flesh."
It is God, the Second Person of the Holy Trinity Who says this. Holy God.
And the following words are not in contradiction as they are so often misinterpreted to be, rather they reinforce the promise and Christ’s recognition that some would not accept this promise, for the spirit working in you gives you the grace to accept this miraculous promise:
 It is the spirit that gives life, the flesh is of no avail; the words that I have spoken to you are spirit and life."
Looking at Christ’s word’s as only symbolic is failing to see Christ’s promise for eternal life; the followers who left were looking at his words not with eyes filled with the spirit–which acknowlege that such a promise from God is quite a real promise, but with eyes that saw only the flesh in his words.
Christ emphasizes that we rely on God to grant us the grace to accept this incredible, incredible promise from the Saviour:
 But there are some of you that do not believe." For Jesus knew from the first who those were that did not believe, and who it was that would betray him.
 And he said, "This is why I told you that no one can come to me unless it is granted him by the Father."