Apparently the “protestant” interpretation was’nt a new innovation.
Augustine
“If the sentence is one of command, either forbidding a crime or vice, or enjoining an act of prudence or benevolence, it is not figurative.** If, however, it seems to enjoin a crime or vice, or to forbid an act of prudence or benevolence, it is figurative.** ‘Except ye eat the flesh of the Son of man,’ says Christ, ‘and drink His blood, ye have no life in you.’ This seems to enjoin a crime or a vice; it is therefore a figure, enjoining that we should have a share in the sufferings of our Lord, and that we should retain a sweet and profitable memory of the fact that His flesh was wounded and crucified for us.” - Augustine (On Christian Doctrine, 3:16:24)
Clement of Alexandria
“Elsewhere the Lord, in the Gospel according to John, brought this out by symbols, when He said: ‘Eat ye my flesh, and drink my blood,’ describing distinctly by **metaphor **the drinkable properties of faith and the promise, by means of which the Church, like a human being consisting of many members, is refreshed and grows, is welded together and compacted of both,–of faith, which is the body, and of hope, which is the soul; as also the Lord of flesh and blood. For in reality the blood of faith is hope, in which faith is held as by a vital principle.” - Clement of Alexandria (The Instructor, 1:6)
Tertullian
“He says, it is true, that ‘the flesh profiteth nothing;’ but then, as in the former case, the meaning must be regulated by the subject which is spoken of. Now, because they thought His discourse was harsh and intolerable, **supposing that He had really and literally enjoined on them to eat his flesh, He, with the view of ordering the state of salvation as a spiritual thing, set out with the principle, ‘It is the spirit that quickeneth;’ and then added, ‘The flesh profiteth nothing,’–meaning, of course, to the giving of life. He also goes on to explain what He would have us to understand by spirit: ‘The words that I speak unto you, they are spirit, and they are life.’ In a like sense He had previously said: ‘He that heareth my words, and believeth on Him that sent me, hath everlasting life, and shall not come into condemnation, but shall pass from death unto life.’ Constituting, therefore, His word as the life-giving principle, because that word is spirit and life, He likewise called His flesh by the same appelation; because, too, the Word had become flesh, we ought therefore to desire Him in order that we may have life, and to devour Him with the ear, and to ruminate on Him with the understanding, and to digest Him by faith. Now, just before the passage in hand, He had declared His flesh to be ‘the bread which cometh down from heaven,’ impressing on His hearers constantly under the figure **of necessary food the memory of their forefathers, who had preferred the bread and flesh of Egypt to their divine calling.” - Tertullian (On the Ressurection of the Flesh, 37)