15 So far I have dealt with the arguments and examples of philosophers. Now I will pass on to the beginning of the human race, that is, to the sphere which belongs to us. I will first point out that Adam received a command in paradise to abstain from one tree though he might eat the other fruit. The blessedness of paradise could not be consecrated without abstinence from food. So long as he fasted, he remained in paradise; he ate, and was cast out; he was no sooner cast out than he married a wife.
While he fasted in paradise he continued a virgin: when he filled himself with food in the earth, he bound himself with the tie of marriage. And yet though cast out he did not immediately receive permission to eat flesh; but only the fruits of trees and the produce of the crops, and herbs and vegetables were given him for food, that even when an exile from paradise he might feed not upon flesh which was not to be found in paradise, but upon grain and fruit like that of paradise.
But afterwards when God saw that the heart of man from his youth was set on wickedness continually, and that His Spirit could not remain in them because they were flesh, He by the deluge passed sentence on the works of the flesh, and, taking note of the extreme greediness of men, gave them liberty to eat flesh: so that while understanding that all things were lawful for them, they might not greatly desire that which was allowed, lest they should turn a commandment into a cause of transgression.
And yet even then, fasting was in part commanded. For, seeing that some animals are called clean, some unclean, and the unclean animals were taken into Noah's ark by pairs, the clean in uneven numbers (and of course the eating of the unclean was forbidden, otherwise the term unclean would be unmeaning), fasting was in part consecrated: restraint in the use of all was taught by the prohibition of some. Why did Esau lose his birthright? Was it not on account of food? And he could not atone with tears for the impatience of his appetite.
The people of Israel cast out from Egypt and on their way to the land of promise, the land flowing with milk and honey, longed for the flesh of Egypt, and the melons and garlic, saying: “Would that we had died by the hand of the Lord in the land of Egypt, when we sat by the flesh pots.” And again, “Who shall give us flesh to eat? We remember the fish which we did eat in Egypt for nought; the cucumbers, and the melons, and the leeks, and the onions, and the garlic: but now our soul is dried away: we have nought save this manna to look to.”
Source: Against Jovinianus (New Advent)