Even if such food changed, it would not become part of the risen body
Athenagoras is answering the objection that human bodies eaten by other humans could be raised, by arguing that even if such food were somehow changed, it would not become a permanent part of the body that is raised.
But suppose someone grants that the food entering from these bodies, and let this be said in the more customary way, even though it is contrary to nature, is separated and transformed into one of the moistening, drying, heating, or cooling substances. Even so, nothing useful will come to them from what has been granted. The bodies that are raised are composed again from their own proper parts, and none of the things mentioned is a part, nor does it hold the relation or order of a part. Nor does it always remain with the parts of the body that are nourished, nor is it raised together with the bodies that are raised, since it no longer contributes anything to life: not blood, not phlegm, not bile, not breath. For the bodies that are nourished will not need then what they once needed, because the need for the things from which they were nourished is destroyed along with the lack and corruption of the things that are nourished.
Then, even if someone supposes that the change from such food reaches as far as flesh, there will still be no necessity that the flesh newly changed from such food, having approached another human being's body, should again serve as a part to complete that body. For the flesh that receives it does not always preserve what it has received, nor is the flesh united to it permanent and remaining with the parts which by nature bind, cover, or warm the flesh selected by nature and grown to those parts, the flesh with which nature completed the life according to nature and the labors in that life.
But neither when the matters just examined are judged as they should be, nor when the arguments developed against them are accepted by concession, is it possible to show that what is said by them is true. Nor could the bodies of human beings ever be blended with bodies of the same human nature, even if through ignorance they are ever robbed of perception by sharing in another such body, even if they are defiled on the spot by a body of the same kind through lack or madness. Unless, of course, we have failed to notice that there are certain human-shaped beasts, or beings with a mixed nature from humans and animals, such as the bolder poets are accustomed to invent.
Greek
Ὅλως δὲ κἂν συγχωρήσῃ τις τὴν ἐκ τούτων εἰσιοῦσαν τροφήν (προσειρήσθω δὲ τοῦτο συνηθέστερον), καίπερ οὖσαν παρὰ φύσιν, διακρίνεσθαι καὶ ματαβάλλειν εἰς ἕν τι τῶν ὑγραινόντων ἢ ξηραινόντων ἢ θερμαινόντων ἢ ψυχόντων, οὐδ᾿ οὕτως ἐκ τῶν συγχωρηθέντων αὐτοῖς γενήσεταί τι προὔργου, τῶν μὲν ἀνισταμένων σωμάτων ἐκ τῶν οἰκείων μερῶν πάλιν συνισταμένων, οὐδενὸς δὲ τῶν εἰρημένων μέρους ὄντος, οὐδὲ τὴν ὡς μέρους ἐπέχοντος σχέσιν ἢ τάξιν, οὐ μὴν οὐδὲ παραμένοντος πάντοτε τοῖς τρεφομένοις τοῦ σώματος μέρεσιν, ἢ συνανισταμένου τοῖς ἀνισταμένοις, οὐδὲν συντελοῦντος ἔτι πρὸς τὸ ζῆν οὐχ αἵματος οὐ φλέγματος οὐ χολῆς οὐ πνεύματος. οὐδὲ γὰρ ὧν ἐδεήθη ποτὲ τὰ τρεφόμενα σώματα, δεηθήσεται καὶ τότε, συνανῃρημένης τῇ τῶν τρεφομένων ἐνδείᾳ καὶ φθορᾷ τῆς ἐξ ὧν ἐτρέφετο χρείας. ἔπειτ' εἰ καὶ μέχρι σαρκὸς φθάνειν τὴν ἐκ τῆς τοιαύτης τροφῆς μεταβολὴν ὑποθοῖτό τις, οὐδ' οὕτως ἀνάγκη τις ἔσται τὴν νεωστὶ μεταβληθεῖσαν ἐκ τῆς τοιᾶσδε τροφῆς σάρκα προσπελάσασαν ἑτέρου τινὸς ἀνθρώπου σώματι πάλιν ὡς μέρος εἰς τὴν ἐκείνου τελεῖν συμπλήρωσιν, τῷ μήτε αὐτὴν τὴν προσλαμβάνουσαν σάρκα πάντοτε φυλάττειν ἣν προσείληφεν, μήτε τὴν ἑνωθεῖσαν ταύτην μόνιμον εἶναι καὶ παραμένειν παραμένειν τοῖς μέρεσιν ἃ συνδεῖν ἢ στέγειν ἢ θάλπειν πέφυκεν τὴν ὑπὸ τῆς φύσεως ἐξειλεγμένην καὶ τούτοις προσπεφυκυῖαν οἷς τὴν κατὰ φύσιν συνεξέπλησε ζωὴν καὶ τοὺς ἐν τῇ ζωῇ πόνους. Ἀλλ᾿ οὔτε γὰρ καθ᾿ ὃ δεῖ κρινομένων τῶν ἔναγχος ἐξητασμένων, οὔτε κατὰ συγχώρησιν παραδεχθέντων τῶν ἐπ᾿ ἐκείνοις γεγυμνασμένων, ἀληθὲς δεικνύναι δυνατὸν τὸ πρὸς αὐτῶν λεγόμενον, οὔτ᾿ ἂν συγκραθείη ποτὲ τὰ τῶν ἀνθρώπων σώματα τοῖς τῆς αὐτῆς οὖσι φύσεως, κἂν ὑπ᾿ ἀγνοίας ποτὲ κλαπῶσι τὴν αἴσθησιν δι᾿ ἑτέρου τινὸς μετασχόντες τοιούτου σώματος, κἂν αὐτόθεν ὑπ᾿ ἐνδείας ἢ μανίας ὁμοειδοῦς τινος μιανθῶσι σώματι· εἴ γε μὴ λελήθασιν ἡμᾶς ἀνθρωποειδεῖς τινες ὄντες θῆρες, ἢ μικτὴν ἔχοντες φύσιν ἐξ ἀνθρώπων καὶ θηρίων, οἵους πλάττειν εἰώθασιν οἱ τολμηρότεροι τῶν ποιητῶν.