Λέγεται δὲ καὶ πρῶτος κρέασιν ἀσκῆσαι ἀθλητάς, καὶ πρῶτόν γ’ Εὐρυμένην, καθά φησι Φαβωρῖνος ἐν τρίτῳ τῶν Ἀπομνημονευμάτων, τῶν πρότερον ἰσχάσι ξηραῖς καὶ τυροῖς ὑγροῖς, ἀλλὰ καὶ πυροῖς σωμασκούντων αὐτούς, καθάπερ ὁ αὐτὸς Φαβωρῖνος ἐν ὀγδόῃ Παντοδαπῆς ἱστορίας φησίν. οἱ δὲ Πυθαγόραν ἀλείπτην τινὰ τοῦτον σιτίσαι τὸν τρόπον, μὴ τοῦτον. τοῦτον γὰρ καὶ τὸ φονεύειν ἀπαγορεύειν, μὴ ὅτι γε ἅπτεσθαι τῶν ζῴων κοινὸν δίκαιον ἡμῖν ἐχόντων ψυχῆς. καὶ τόδε μὲν ἦν τὸ πρόσχημα· τὸ δ’ ἀληθὲς τῶν ἐμψύχων ἀπηγόρευεν ἅπτεσθαι συνασκῶν καὶ συνεθίζων εἰς εὐκολίαν βίου τοὺς ἀνθρώπους, ὥστε εὐπορίστους αὐτοῖς εἶναι τὰς τροφὰς ἄπυρα προσφερομένοις καὶ λιτὸν ὕδωρ πίνουσιν· ἐντεῦθεν γὰρ καὶ σώματος ὑγίειαν καὶ ψυχῆς ὀξύτητα περιγίνεσθαι. ἀμέλει καὶ βωμὸν προσκυνῆσαι μόνον ἐν Δήλῳ τὸν Ἀπόλλωνος τοῦ γενέτορος, ὅς ἐστιν ὄπισθεν τοῦ Κερατίνου, διὰ τὸ πυροὺς καὶ κριθὰς καὶ πόπανα μόνα τίθεσθαι ἐπ’ αὐτοῦ ἄνευ πυρός, ἱερεῖον δὲ μηδέν, ὥς φησιν Ἀριστοτέλης ἐν Δηλίων πολιτείᾳ.
(Diogenes Laertius, Bioi kai Gnōmai 8.12-13)
He is also said to have been the first to diet athletes on meat, trying first with Eurymenes—so we learn from Favorinus in the third book of his Memorabilia—whereas in former times they had trained on dried figs, on butter, and even on wheat-meal, as we are told by the same Favorinus in the eighth book of his Miscellaneous History. Some say it was a certain trainer named Pythagoras who instituted this diet, and not our Pythagoras, who forbade even the killing, let alone the eating, of animals which share with us the privilege of having a soul. This was the excuse put forward; but his real reason for forbidding animal diet was to practise people and accustom them to simplicity of life, so that they could live on things easily procurable, spreading their tables with uncooked foods and drinking pure water only, for this was the way to a healthy body and a keen mind. Of course the only altar at which he worshipped was that of Apollo the Giver of Life, behind the Altar of Horns at Delos, for thereon were occurred flour and meal and cakes, without the use of fire, and there was no animal victim, as we are told by Aristotle in his Constitution of Delos. (tr. Robert Drew Hicks)