The answer does not lie exclusively in the words of institution (This my body, etc) although that's the way most of these debates go. It's also in what he says afterwards about the meal and the Apostles repeating it after he's gone from Earth.
Because that wording suggests a transcendent meaning, the bread and wine appear to mean more than just symbols, not even symbols which call valuable memories to mind when the Eucharist is celebrated, or bond the communicants together. In addition, there is evidence from very early times that the first Christians saw the meal as more than just a symbol.
Therefore, we believe that in some way, it is Christ's person. But at the same time, we have no reason to think that it is LITERALLY parts of that same body he used on Earth, and we know that this idea didn't come into play until well into the Middle Ages. Transubstantiation is purely and completely a theory out of the Medieval mindset, as well as being dated from the Middle Ages, not the Apostolic period.
.
St.
Justin Martyr offers a glimpse of the Eucharistic sacrifice in
150 AD and this foodis called among us Eucaristia [the Eucharist], of which no one is allowed to partake but the man who believes that the things which we teach are true, and who has been washed with the washing that is for the remission of sins, and unto regeneration, and who is so living as Christ has enjoined. For not as common bread and common drink do we receive these; but in like manner as Jesus Christ our Savior, having been made flesh by the Word of God, had both flesh and blood for our salvation, so likewise have we been taught that the food which is blessed by the prayer of His word, and from which our blood and flesh
by transmutation are nourished, is the flesh and blood of that Jesus who was made flesh (
First Apology,1, 62).
Though the early Fathers did not use this exact terminology, the teaching was essential to their theology. The Fathers unanimously held to the Real Presence of Christ in the Eucharist.
Synonyms: alteration, change, changeover, evolution, mutation, rebirth, transfiguration, transfigurement, transformation, translation, transmogrification,
transmutation, transubstantiation
Ignatius received his episcopal consecration
at the hands of the Apostles themselves ("Hom. in St. Ig.", IV. 587). Natalis Alexander quotes Theodoret to the same effect (III, xii, art. xvi, p. 53).
He constitutes one
of the most important links between the Apostles and the Fathers of the early Church. Receved from the Apostles themselves.
I desire the Bread of God, the heavenly Bread, the Bread of Life, which is the flesh of Jesus Christ, the Son of God, who became afterwards of the seed of David and Abraham; I wish the drink of God, namely His blood, which is incorruptible love and eternal life.
--we believe because he recieved this directly from the Apostles backed up by scripture.
Protestant early Church historian J. N. D. Kelly writes that in the early Church "the Eucharist was regarded as the distinctively Christian sacrifice. . . . Malachis prediction (1:1011) that the Lord would reject Jewish sacrifices and instead would have "a pure offering" made to him by the Gentiles in every place was seized upon by Christians as a prophecy of the Eucharist. The Didache indeed actually applies the term thusia, or sacrifice, to the Eucharist. . . .
"It was natural for early Christians to think of the Eucharist as a sacrifice. The fulfillment of prophecy demanded a solemn Christian offering, and the rite itself was wrapped in the sacrificial atmosphere with which our Lord invested the Last Supper. The words of institution, Do this (touto poieite), must have been charged with sacrificial overtones for second-century ears; Justin at any rate understood them to mean, Offer this. . . . The bread and wine, moreover, are offered for a memorial (eis anamnasin) of the passion, a phrase which in view of his identification of them with the Lords body and blood implies much more than an act of purely spiritual recollection" (J. N. D. Kelly, Early Christian Doctrines [Full Reference], 1967).
There is no sacrifice without a body being presant.