Get Good at Fasting
Eating and drinking are not to be done without a reasonable object. The objects to which these actions are ordered, that is the reason they were created, are the health of the body (for growth, energy, medicine, etc.) and mutual association and concourse with our fellow man. Eating for the pleasure of the palate alone is disordered, is not why food was made by God, and is the sin of gluttony. As we will see, this sin, if not resisted can not only become mortal, but can also lead to the mortal sins of lust and forgetfulness of God.
Decree of the Holy Office under Pope Innocent XI, March 4, 1679: "Eating and drinking even to satiety for pleasure only, are not sinful, provided this does not stand in the way of health, since any natural appetite can licitly enjoy its own actions." - CONDEMNED (Denzinger 1158)
St. Francis de Sales, Introduction into the Devout Life, Third Part, Ch. 39: "Just as eating not merely for the preservation of life but to maintain the mutual association and consideration we owe one another is an extremely just and virtuous act, so also mutual, lawful satisfaction of both parties in holy matrimony is called a debt by St. Paul."
Gluttony, rooted in the desire, carried out in the deed
St. Thomas Aquinas, Summa Theologica, Secunda Secundae Partis, Q. 148, Art. 1: "Gluttony denotes, not any desire of eating and drinking, but an inordinate desire. Now desire is said to be inordinate through leaving the order of reason, wherein the good of moral virtue consists: and a thing is said to be a sin through being contrary to virtue. Wherefore it is evident that gluttony is a sin.
"That which goes into man by way of food, by reason of its substance and nature, does not defile a man spiritually. But the Jews, against whom our Lord is speaking, and the Manichees deemed certain foods to make a man unclean, not on account of their signification, but by reason of their nature [Cf. I-II, 102, 6, ad 1]. It is the inordinate desire of food that defiles a man spiritually.
"As stated above, the vice of gluttony does not regard the substance of food, but in the desire thereof not being regulated by reason. Wherefore if a man exceed in quantity of food, not from desire of food, but through deeming it necessary to him, this pertains, not to gluttony, but to some kind of inexperience. It is a case of gluttony only when a man knowingly exceeds the measure in eating, from a desire for the pleasures of the palate."
Gluttony is serious enough to lead man away from God:
St. Thomas Aquinas, Summa Theologica, Secunda Secundae Partis, Q. 148, Art. 2: "In so far as it turns man away from his last end, gluttony is opposed to the love of God, who is to be loved, as our last end, above all things: and only in this respect is gluttony a mortal sin.
"Gluttony is said to bring virtue to naught, not so much on its own account, as on account of the vices which arise from it. For Gregory says (Pastor. iii, 19): "When the belly is distended by gluttony, the virtues of the soul are destroyed by lust.""
Gluttony leads to mortal sins of the flesh:
St. Thomas Aquinas, Summa Theologica, Secunda Secundae Partis, Q. 148, Art. 6: "Further, the uncleanness which is particularly the result of gluttony ..."
"On the part of the body, mention is made of "uncleanness," which may refer either to the inordinate emission of any kind of superfluities, or especially to the emission of the semen. Hence a gloss on Ephesians 5:3, "But fornication and all uncleanness," says: "That is, any kind of incontinence that has reference to lust."
Avoid gluttony, lest you be an enemy of Christ, ending in destruction
Philippians 3:18-19: "For many walk, of whom I have told you often (and now tell you weeping), that they are enemies of the cross of Christ; Whose end is destruction; whose God is their belly; and whose glory is in their shame; who mind earthly things."
The Revelations of St. Birgitta of Sweden, Book 4, Chapter 89: "The knight's coat of mail represents abstinence. Just as a coat of mail consists of many small rings of chain, so too abstinence consists of many virtues, for example, abstinence from immoral sights or things affecting the other senses, from gluttony and lust and superfluity, and from many other things that St. Benedict laid down as forbidden. One cannot put this coat of mail on alone without another's help. Therefore, my Mother, the Virgin Mary, should be invoked and venerated, for every good example and type of virtue are to be found in her. If she is steadfastly invoked, she will indicate to your spirit all the perfect types of abstinence."