Observe then, O thou [disciple], very carefully and with discerning knowledge, that not all hunger is the hunger of nature, and that not all meat is the meat which satisfieth want, and observe the different kinds of hunger, and distinguish and select with knowledge thine own hunger from among them. One kind of hunger belongeth to youth, and another ariseth from weakness, and another from excessive emptiness, and another from habit, and another from idleness of the thoughts which have nothing wherewith to occupy themselves, and another from the feebleness of the thoughts, and another from the daily cutting off which happeneth unto the body, and another from the coldness of the body which seeketh to be made warm [p. by meat, and another which excessive labour produceth; these and such like things are the causes of hunger, besides there being some men also whose hunger is not a healthy hunger. Therefore many men are able to bear hunger from the beginning of the day, and some are an hungered at the second hour, and others at the fourth, and others at the sixth, and others at the ninth, and others in the evening, and others can endure the hunger of the close of the day until the vigil of the night, and others continue to fast until the third hour; and when they have arrived at the number of a double vigil their natural hunger hath entirely ceased in them, because the natural heat which is stirred up in the body taketh the place of meat to them. And when from these things thou dost understand the varieties of hunger which are born in thee, thou must distinguish and select from them all the hunger which cometh of thy need, but thou must from time to time restrain even this, in order that the endurance of thy affliction may be the more made manifest, by which thy love unto God is made known. Take heed then that the hunger of lust lead thee not astray and thou imagine it to be the hunger of nature. Now the real hunger of nature is not the want of food in the stomach, but the want of the power of the food in all the members, for when the members have put off the power of food, and have put on in its stead weakness, and although thou callest unto them they respond not with whatever service thou wishest, this is natural hunger; and thou must therefore take carefully such food as will restore the power to the members, being watchful of thy thought that it be not mingled with the body in the meat, and thou must make the lust which is in thee to sleep, lest it be roused up and the lust for food be excited by thee instead of by want; and if this happeneth thy meal is one to be blamed, even though thou takest food because of hunger, and eatest sparingly.
Philoxenus, Ascetic Discourses (1894) pp.403-471. Discourse 11 — On Abstinence