I think you can answer this by reading this piece by Benedict XVI on fasting as a spiritual practice:
Part I of II
MESSAGE OF HIS HOLINESS
BENEDICT XVI
FOR LENT 2009
“He fasted for forty days and forty nights,
and afterwards he was hungry” (Mt 4,1-2)
Dear Brothers and Sisters!
At the beginning of Lent, which constitutes an itinerary of more intense spiritual training, the Liturgy sets before us again three penitential practices that are very dear to the biblical and Christian tradition – prayer, almsgiving, fasting – to prepare us to better celebrate Easter and thus experience God’s power that, as we shall hear in the Paschal Vigil, “dispels all evil, washes guilt away, restores lost innocence, brings mourners joy, casts out hatred, brings us peace and humbles earthly pride” (Paschal Præconium). For this year’s Lenten Message, I wish to focus my reflections especially on the value and meaning of fasting. Indeed, Lent recalls the forty days of our Lord’s fasting in the desert, which He undertook before entering into His public ministry. We read in the Gospel: “Jesus was led up by the Spirit into the wilderness to be tempted by the devil. He fasted for forty days and forty nights, and afterwards he was hungry” (Mt 4,1-2). Like Moses, who fasted before receiving the tablets of the Law (cf. Ex 34,28) and Elijah’s fast before meeting the Lord on Mount Horeb (cf. 1 Kings 19,8), Jesus, too, through prayer and fasting, prepared Himself for the mission that lay before Him, marked at the start by a serious battle with the tempter.
We might wonder what value and meaning there is for us Christians in depriving ourselves of something that in itself is good and useful for our bodily sustenance. The Sacred Scriptures and the entire Christian tradition teach that fasting is a great help to avoid sin and all that leads to it. For this reason, the history of salvation is replete with occasions that invite fasting. In the very first pages of Sacred Scripture, the Lord commands man to abstain from partaking of the prohibited fruit: “You may freely eat of every tree of the garden; but of the tree of the knowledge of good and evil you shall not eat, for in the day that you eat of it you shall die” (Gn 2, 16-17). Commenting on the divine injunction, Saint Basil observes that “fasting was ordained in Paradise,” and “the first commandment in this sense was delivered to Adam.” He thus concludes: “ ‘You shall not eat’ is a law of fasting and abstinence” (cf. Sermo de jejunio: PG 31, 163, 98). Since all of us are weighed down by sin and its consequences, fasting is proposed to us as an instrument to restore friendship with God. Such was the case with Ezra, who, in preparation for the journey from exile back to the Promised Land, calls upon the assembled people to fast so that “we might humble ourselves before our God” (8,21). The Almighty heard their prayer and assured them of His favor and protection. In the same way, the people of Nineveh, responding to Jonah’s call to repentance, proclaimed a fast, as a sign of their sincerity, saying: “Who knows, God may yet repent and turn from his fierce anger, so that we perish not?” (3,9). In this instance, too, God saw their works and spared them.
In the New Testament, Jesus brings to light the profound motive for fasting, condemning the attitude of the Pharisees, who scrupulously observed the prescriptions of the law, but whose hearts were far from God. True fasting, as the divine Master repeats elsewhere, is rather to do the will of the Heavenly Father, who “sees in secret, and will reward you” (Mt 6,18). He Himself sets the example, answering Satan, at the end of the forty days spent in the desert that “man shall not live by bread alone, but by every word that proceeds from the mouth of God” (Mt 4,4). The true fast is thus directed to eating the “true food,” which is to do the Father’s will (cf. Jn 4,34). If, therefore, Adam disobeyed the Lord’s command “of the tree of the knowledge of good and evil you shall not eat,” the believer, through fasting, intends to submit himself humbly to God, trusting in His goodness and mercy.
The practice of fasting is very present in the first Christian community (cf. Acts 13,3; 14,22; 27,21; 2 Cor 6,5). The Church Fathers, too, speak of the force of fasting to bridle sin, especially the lusts of the “old Adam,” and open in the heart of the believer a path to God. Moreover, fasting is a practice that is encountered frequently and recommended by the saints of every age. Saint Peter Chrysologus writes: “Fasting is the soul of prayer, mercy is the lifeblood of fasting. So if you pray, fast; if you fast, show mercy; if you want your petition to be heard, hear the petition of others. If you do not close your ear to others, you open God’s ear to yourself” (Sermo 43: PL 52, 320. 322).
