In the Eucharist, the baptized person receives Christ Who, in His Body and Blood, gives Himself entirely, not just as man, but also as God, since "in Him dwells all the fullness of the Godhead.." ( Colossians2:9)
Dr. Jean Claude Larchet
Though it is Christ's Body that the faithful receives as food, it is His whole Being (body, soul, and spirit) that they assimilate. Christ's Body spreads to all the bodily members of the communicant and also to all the faculties of the soul, mingling intimately with them. Thus the communicant becomes a "Christ-Bearer", for through communion there is an indwelling of Christ in the Christian and of the Christian in Christ: "He who eats My Flesh and drinks My Blood abides in Me, and I in him." John 6:56 By this sacrament, notes St. Gregory of Nyssa, God infused Himself into perishable humanity for this purpose, namely that by this communion with Deity mankind might at the same time be deified.
But even before that stage is reached, this spiritual food nourishes, purifies, sustains, fortifies, strengthens, and protects both body and soul against all evil.
Though absorbed by the body and bringing into play its digestive functions, it is nonetheless very different from ordinary food, and it is in quite another way that, for the recipient, it is a source of life. As St. Nicholas Cabasilas explains,
Man lives because of food, but not in the same way in this sacred rite. Since natural food is not itself living it does not of itself infuse life into us... but the Bread of Life is Himself living, and through Him those to who He imparts Himself truly live. While natural food is changed into him who feeds on it...here it is entirely opposite. The Bread of Life Himself changes him who feeds on Him and transforms and assimilates him into Himself.