Cassian’s teacher at Constantinople has been John Chrysostom. Although he does not lay down guidelines for monastic formation in the same systematic way, Chrysostom promotes a similar spirit of moderation, which appears to have had an effect on his pupil. He writes:
Fasting is a medicine; but a medicine, though it be never so profitable, becomes frequently useless owing to the unskilfulness of him who employs it. For it is necessary to know, moreover, the time when it should be applied, and the requisite quantity of it; and the temperament of body that admits it; and the nature of the country, and the season of the year; and the corresponding diet; as well as various other particulars; any of which, if one overlooks, he will mar all the rest that have been named.
By characterizing fasting as a medicine, Chrysostom makes clear that it exists to remedy human weakness.
Theology on the Menu: Asceticism, Meat and Christian Diet
by David Grumett, Rachel Muers