There is an old saying: 'Excesses meet.' Too much fasting and too much eating come to the same end. Keeping too long a vigil brings the same disastrous cost as ... sluggishness... Too much self-denial brings weakness and induces the same condition as carelessness. Often I have seen men who would not be snared by gluttony fall, nevertheless, through immoderate fasting and tumble in weakness into the very urge which they had overcome. Unmeasured vigils and foolish denial of rest overcame those whom sleep could not overcome. Therefore, 'fortified to right and to left in the armor of justice,' as the apostle says (2 Cor. 6:7), life must be lived with due measure and, with discernment for a guide, the road must be traveled between the two kinds of excess so that in the end we may not allow ourselves to be diverted from the pathway of restraint which has been laid down for us nor fall through dangerous carelessness into the urgings of gluttony and self-indulgence.
-St. John Cassian, Conferences, Conference Two: On Discernment no. 16; Paulist Press pg. 76, 5th century