I think there may be an example that does affirm the definition: e.g. John 16:20, "Your sorrow shall be turned into joy." This was a real transubstantiation.
The doctrine hinges upon "This is my body" (touto esti to soma mou). This is no more literal than to say "The good seed are the children of the kingdom." or The field is the world". He is speaking figuratively.
He is using the figure Metaphor; or Representation. Which is a declaration that one thing is (or represents) another; or, Comparison by Representation. From the Greek-metaphora, a transference, or carrying over or across. From (meta), beyond or over, and (Pherein), to carry. The Metaphor declares that one thing IS the other.
The Metaphor is not so true to fact as the Simile, but is much truer to feeling. The two nouns themselves must both be mentioned, and are always to be taken in their absolutely literal sense, or else no one can tell what they mean. The figure lies wholly in the verb, and not in either of the two nouns: and it is a remarkable fact that, when a pronoun is used instead of one of the nouns (as it is here), and the two nouns are of different genders, the pronoun is always made to agree in gender with that noun to which the meaning is carried across, and not with the noun from which it is carried, and to which it properly belongs. This at once shows us that a figure is being employed; when a pronoun, which ought, according to the laws of language, to agree in gender with its own noun, is changed, and made to agree with the noun which, by Metaphor, represents it.
In our example, the pronoun, "this" (touto), is neuter, and is thus made to agree with "body" (swma), which is neuter, and not with bread (aptos, artos), which is masculine. This is always the case in Metaphors. Here are a few other examples to illustrate.
In Zech. 5:8, "This is wickedness." Here, "this" (fem.) does not agree with "ephah" (to which it refers), which is neuter, but with "wickedness, " which is feminine.
In Zech. 5:3, "This is the curse." "This" (fem.) agrees with "curse", which is feminine, and not with "flying roll", which is neuter, (to which it refers).
In Matt.13:38, "The good seed are the children of the kingdom." Here, "these" (masc.) agrees with "children of the kingdom" (masc.), and not with seed, which is neuter.
What this is showing is that in a Metaphor, the two nouns (or pronoun and noun) are always literal, and that the figure lies only in the verb.
"This is (i.e., represents) my body," is an undoubted Metaphor. "He took the cup...saying...this is my blood." Here we have a pair of metaphors. In the former one, "this" refers to "bread", and it is claimed that "is" means changed into the "body" of Christ. In the latter, "this" refers to "the cup", but it is not claimed that the cup is changed into "blood". The difference of treatment which the same figure meets with in these two verses is proof that the former is wrong.
In 1Cor. 11:25 we read "this cup is the new covenant." How does this "cup" become transubstantiated into a "covenant"?
Additionally, the verb, (eimi), I am, or the infinitive of it, to be, means to be in the sense of signifying, amounting to. e.g. Mt.9:13, 'But go ye and learn what that means"
Mt.12:7, "But if ye had known what this means".
Acts. 10:7, "Now, while Peter doubted in himself what this vision should mean"
On the other hand, if an actual change is meant, then there must be a verb which plainly and actually says so; for the verb "to be" never has or conveys any idea of such a change.
The usual verb to express such a change is (ginomai), which means to be or become. Mk.9:39, 'There was(i.e. became) a great calm,"
Lk.4:3, "Command this stone that it be made (i.e. changed into) bread."
If Jesus had meant that the bread had become His body, that is the verb He would have necessarily used. The fact that He did not use it, but instead used the simple verb (eimi), i.e., "is" proves conclusively that no change was meant, and that only representation was intended.
From all this it is clear that the words, "This is my body" means "This (bread) represents my body."