9 In saying this, I do not of course condemn food which God created to be enjoyed with thanksgiving, but I seek to remove from youths and girls what are incentives to sensual pleasure. Neither the fiery Etna nor the country of Vulcan, nor Vesuvius, nor Olympus, burns with such violent heat as the youthful marrow of those who are flushed with wine and filled with food. Many trample covetousness under foot, and lay it down as readily as they lay down their purse. An enforced silence serves to make amends for a railing tongue. The outward appearance and the mode of dress can be changed in a single hour. All other sins are external, and what is external can easily be cast away. Desire alone, implanted in men by God to lead them to procreate children, is internal; and this, if it once oversteps its own bounds, becomes a sin, and by a law of nature cries out for sexual intercourse. It is therefore a work of great merit, and one which requires unremitting diligence to overcome that which is innate in you; while living in the flesh not to live after the flesh; to strive with yourself day by day and to watch the foe shut up within you with the hundred eyes of the fabled Argus. This is what the apostle says in other words: “Every sin that a man does is without the body; but he that commits fornication sins against his own body.” Physicians and others who have written on the nature of the human body, and particularly Galen in his books entitled On matters of health, say that the bodies of boys and of young men and of full grown men and women glow with an interior heat and consequently that for persons of these ages all food is injurious which tends to promote this heat: while on the other hand it is highly conducive to health in eating and in drinking to take things cold and cooling. Contrariwise they tell us that warm food and old wine are good for the old who suffer from humours and from chilliness. Hence it is that the Saviour says “Take heed to yourselves lest at any time your hearts be overcharged with surfeiting and drunkenness, and cares of this life.” So too speaks the apostle: “Be not drunk with wine, wherein is excess.” No wonder that the potter spoke thus of the vessel which He had made when even the comic poet whose only object is to know and to describe the ways of men tells us that
Where Ceres fails and Liber, Venus droops.
Source: Letters (New Advent)