http://www.catholic.com/thisrock/2001/0103sbs.aspIn the Old Testament, there are several occasions where angels take on human appearances in order to carry out the work of God. Now, is the angel an angelic being or a human being? It would not look angelic. Through touch, smell, sight, et cetera it would appear to be fully human. But it is an angel. If an angel can take on human form, God is infinitely able to humble himself under the appearance of bread in order that we might receive him. In the words the Eucharistic hymn Tantum Ergo, "What our senses fail to fathom let us grasp through faith’s consent."
Cannibalism is when one individual physically eats the human flesh off of another’s body. Catholic or not, the words in John 6 do sound cannibalistic. Even a Fundamentalist would have to say that he eats the flesh of Christ and drinks his blood in a symbolic manner so as to concur with the passage. By the same allowance, Catholics eat the flesh of Christ and drink his blood in a sacramental way. Neither the Protestant nor the Catholic appears to be doing anything cannibalistic, though.
It would have been cannibalism is if a disciple two thousand years ago had tried literally to eat Jesus by sinking his teeth into his arm. Now that our Lord is in heaven with a glorified body and made present under the appearance of bread in the Eucharist, cannibalism is not possible.
Transubstantiation was taught by the Church Fathers long before anyone had ever heard of the term (see "The Fathers Know Best," page 34). See, for example, the citation from Justin Martyr’s First Apology (A.D. 151): "The food which has been made into the Eucharist by the Eucharistic prayer set down by him, and by the change of which our blood and flesh is nurtured, is both the flesh and the blood of that incarnated Jesus."
The evidence in favor of the Real Presence in the writings of the Church Fathers is compelling and unanimous. In fact, it was not until Berengarius of Tours in the eleventh century that the teaching was denied.