Objection 1. It would seem that abstinence is not a special virtue. For every virtue is praiseworthy by itself. But abstinence is not praiseworthy by itself; for Gregory says (Pastor. iii, 19) that "the virtue of abstinence is praised only on account of the other virtues." Therefore abstinence is not a special virtue.
Objection 2. Further, Augustine [Fulgentius] says (De Fide ad Pet. xlii) that "the saints abstain from meat and drink, not that any creature of God is evil, but merely in order to chastise the body." Now this belongs to chastity, as its very name denotes. Therefore abstinence is not a special virtue distinct from chastity.
Objection 3. Further, as man should be content with moderate meat, so should he be satisfied with moderate clothes, according to 1 Timothy 6:8, "Having food, and wherewith to be covered, with these we should be [Vulgate: 'are'] content." Now there is no special virtue in being content with moderate clothes. Neither, therefore, is there in abstinence which moderates food.
On the contrary, Macrobius [In Somn. Scip. i, 8 reckons abstinence as a special part of temperance.
I answer that, As stated above (136, 1; 141, 3) moral virtue maintains the good of reason against the onslaught of the passions: hence whenever we find a special motive why a passion departs from the good of reason, there is need of a special virtue. Now pleasures of the table are of a nature to withdraw man from the good of reason, both because they are so great, and because food is necessary to man who needs it for the maintenance of life, which he desires above all other things. Therefore abstinence is a special virtue.
Reply to Objection 1. Virtues are of necessity connected together, as stated above (I-II, 65, 1). Wherefore one virtue receives help and commendation from another, as justice from fortitude. Accordingly in this way the virtue of abstinence receives commendation on account of the other virtues.
Reply to Objection 2. The body is chastised by means of abstinence, not only against the allurements of lust, but also against those of gluttony: since by abstaining a man gains strength for overcoming the onslaughts of gluttony, which increase in force the more he yields to them. Yet abstinence is not prevented from being a special virtue through being a help to chastity, since one virtue helps another.
Reply to Objection 3. The use of clothing was devised by art, whereas the use of food is from nature. Hence it is more necessary to have a special virtue for the moderation of food than for the moderation of clothing.
Source: Summa Theologica (New Advent)