Thomas Aquinas, Compendium of Theology

These remarks about the integrity of risen men should be understood as referring to whatever pertains to the true state of human nature. What is not required for the reality of human nature, will not be resumed by risen man. Thus, if all the accretion of matter from the food that has been changed into flesh and blood were to be resumed, the size of risen man would exceed all bounds. The proper condition of any nature is regulated by its species and form. Accordingly all the parts that are consonant with the human species and form will be integrally present in risen man: not only organic parts, but other parts of like nature, such as flesh and sinews, which enter into the composition of the various organs. Of course, not all the matter that was ever contained in those parts during man's natural life will again be taken up, but only so much as will be enough to constitute the species of the parts in integrity.

Even though not all the material elements ever possessed by man will arise, we cannot say on this account that man will not be the same individual, or that he will not be complete. During the course of the present life, man evidently remains numerically the same from birth to death. Nevertheless the material composition of his parts does not remain the same, but undergoes gradual flux and reflux, in somewhat the way that the same fire is kept up although some logs are consumed and others are fed to the blaze. Man is whole when his species and the quantity due to his species are preserved intact.