Objection 1. It would seem that in the state of innocence man did not require food. For food is necessary for man to restore what he has lost. But Adam's body suffered no loss, as being incorruptible. Therefore he had no need of food.
Objection 2. Further, food is needed for nourishment. But nourishment involves passibility. Since, then, man's body was impassible; it does not appear how food could be needful to him.
Objection 3. Further, we need food for the preservation of life. But Adam could preserve his life otherwise; for had he not sinned, he would not have died. Therefore he did not require food.
Objection 4. Further, the consumption of food involves voiding of the surplus, which seems unsuitable to the state of innocence. Therefore it seems that man did not take food in the primitive state.
On the contrary, It is written (Genesis 2:16): "Of every tree in paradise ye shall [Vulgate 'thou shalt'] eat."
I answer that, In the state of innocence man had an animal life requiring food; but after the resurrection he will have a spiritual life needing no food. In order to make this clear, we must observe that the rational soul is both soul and spirit. It is called a soul by reason of what it possesses in common with other souls--that is, as giving life to the body; whence it is written (Genesis 2:7): "Man was made into a living soul"; that is, a soul giving life to the body. But the soul is called a spirit according to what properly belongs to itself, and not to other souls, as possessing an intellectual immaterial power.
Thus in the primitive state, the rational soul communicated to the body what belonged to itself as a soul; and so the body was called "animal" [From 'anima', a soul; Cf. 1 Corinthians 15:44 seqq.], through having its life from the soul. Now the first principle of life in these inferior creatures as the Philosopher says (De Anima ii, 4) is the vegetative soul: the operations of which are the use of food, generation, and growth. Wherefore such operations befitted man in the state of innocence. But in the final state, after the resurrection, the soul will, to a certain extent, communicate to the body what properly belongs to itself as a spirit; immortality to everyone; impassibility, glory, and power to the good, whose bodies will be called "spiritual." So, after the resurrection, man will not require food; whereas he required it in the state of innocence.
Reply to Objection 1. As Augustine says (QQ. Vet. et Nov. Test. qu. 19 [Works of an anonymous author, among the supposititious works of St. Augustine): "How could man have an immortal body, which was sustained by food? Since an immortal being needs neither food nor drink." For we have explained (1) that the immortality of the primitive state was based on a supernatural force in the soul, and not on any intrinsic disposition of the body: so that by the action of heat, the body might lose part of its humid qualities; and to prevent the entire consumption of the humor, man was obliged to take food.
Reply to Objection 2. A certain passion and alteration attends nutriment, on the part of the food changed into the substance of the thing nourished. So we cannot thence conclude that man's body was passible, but that the food taken was passible; although this kind of passion conduced to the perfection of the nature.
Reply to Objection 3. If man had not taken food he would have sinned; as he also sinned by taking the forbidden fruit. For he was told at the same time, to abstain from the tree of knowledge of good and evil, and to eat of every other tree of Paradise.
Reply to Objection 4. Some say that in the state of innocence man would not have taken more than necessary food, so that there would have been nothing superfluous; which, however, is unreasonable to suppose, as implying that there would have been no faecal matter. Wherefore there was need for voiding the surplus, yet so disposed by God as to be decorous and suitable to the state.
Source: Summa Theologica (New Advent)