In the combox at another blog a fellow by the name of Richard A Imgrund wrote the follwoing:
Besides, the DRB gives us, in Matthew’s rendering of the Lord’s Prayer, “give us this day our supersubstantial bread”, which is a literal rendering of the Latin which is a literal rendering of the Greek. Not “daily” bread, which makes it pretty clear Christ was talking about the Eucharist.
I planned on answering hin there, but thought it would be interesting to take it up on my own blog.
No, I wouldn’t say that Matt 6:11 is ‘really’ about the Eucharist. That rests on a misunderstanding of the latin word supersubstantialis. One assumes, because of the substantialis, that St. Jerome (who made the Vulgate translation) had the Eucharist in mind. And that might be right, but that is another matter entirely.
I agree that on some level this is a reference to the Eucharist, since it is talking about bread. (This would be a spiritual reading of the text.) But neither the latin supersubstantialis nor the greek ἐπιούσιος is a reference to transubstantiation. According to BDAG there is some doubt as to what ἐπιούσιος means, but the three most probable possibilities is these: (1) [bread] that is necessary for existence; (2) [bread] for the current day, for today; or (3) [bread] for the next day.
I think that the first reading is the best one, seeing the greek adjective ἐπιούσιος as derived from the preposition ἐπί (’at, over, to,’ etc.) + the noun οὐσία (‘being, existence’). This is reflected in the Vulgate’s panis supersubstantialis. That doesn’t, however, have anything to do with transubstantiation. It just means the bread needed for existence; needed to uphold one’s ‘substance.’ In one of the shows at Catholic Answers Live, Jimmy Akin said that supersubstantialis had nothing to do with transubstantiation, and that the best rendition of it in english was ‘life-sustaining.’
So a good translation might go something like this: “Give us this day our life-sustaining bread.”
That doesn’t mean, however, that one cannot interpret ‘give us this day our daily bread’ in a spiritual way, referring to the Eucharist, in addition to a literal reading. But that is a spiritual reading of the text, a reading that should not trump a literal reading.
 DRB = Douay-Rheims Bible, a Catholic english translation of the Vulgate.