John Cassian on Fasting

I shall speak first about control of the stomach, the opposite to gluttony, and
about how to fast and what and how much to eat. I shall say nothing on my own
account, but only what I have received from the Holy Fathers. They have not
given us only a single rule for fasting or a single standard and measure for
eating, because not everyone has the same strength; age, illness or delicacy of
body create differences. But they have given us all a single goal: to avoid
over-eating and the filling of our bellies... A clear rule for self-control
handed down by the Fathers is this: stop eating while still hungry and do not
continue until you are satisfied.

John Cassian