No Single Rule of Fasting

So in the matter of fasting a single rule cannot easily be kept, because not everyone has the same strength; nor is fasting, like the other virtues, acquired by steadiness of mind alone. Since it does not depend only on firmness of mind, but has to do with what the body can bear, we have received this explanation of it, which has been handed down to us: the time, manner and kind of meal differ according to the differing condition of the body, the age and the sex; but there is one and the same rule of restraint for everyone as regards self-control of mind and the virtue of the spirit. [a]

For not everyone can extend his fast for a week, or put off eating through a fast of two or three days. Many who are worn out with sickness, and especially with old age, cannot bear a fast even until sunset without suffering. The poor food of soaked beans does not agree with everybody; a sparing diet of fresh vegetables does not suit everyone; nor is a scanty meal of dry bread allowed to all alike. One man is not satisfied with about a pound and a half; for another a meal of three-quarters of a pound, or about six ounces, is too much. But in all these cases there is one aim and object of self-control: that no one should overload himself through gluttony beyond the measure of his appetite. For it is not only the kind but also the quantity of food taken that dulls the keenness of the mind, and when the soul as well as the flesh is glutted, it kindles the deadly, fiery spur to vice.