Fasting Prescribed in All Religions
In English "fasting" means to abstain from food or from certain kinds of food voluntarily, as an observance of a holy day or as a token of grief, sorrow, or repentance.
This practice can be found in most of the major religions of the world. For example, in Hinduism, fasting in Sanskrit is called upavaasa. Devout Hindus observe fasting on special occasions as a mark of respect to their personal gods or as a part of their penance. Most devout Indians fast regularly or on special occasions like festivals. On such days they do not eat at all, eat once or make do with fruits or a special diet of simple food.
 For Jews, the day Yom Kippur ("Day of Atonement") is the last of the Ten Days of Repentance observed on the 10th of Tishri. It is forbidden on that day to eat, drink, wash, wear leather, or have sexual relations. In addition, prohibitions on labor similar to those on the Sabbath are in force.
 It should also be noted that Moses (peace be upon him) is recorded in the Torah to have fasted. "And he was there with the Lord 40 days and 40 nights, he neither ate bread not drank water." (Exodus 34:28) For Catholics among Christians, Lent is the major season of fasting, imitative of the forty-day fast of Jesus (peace be upon him). In the fourth century, it was observed as six weeks of fasting before Easter or before Holy Week. It was adjusted to forty days of actual fasting in most places in the seventh century.
 Jesus (peace be upon him) is recorded in the Gospels to have fasted like Moses. "And he fasted 40 days and 40 nights, and afterward he was hungry." (Matthew 4:2 & Luke 4:2)
It is in this context that God states in the Quran: "O believers! Fasting has been prescribed for you as it was prescribed for those before you in order that you become more conscious of God." (Quran 2:183)
Among the Best Righteous Deeds
Although in most religions, fasting is for expiation of sin or atonement for sin, in Islam it is primarily to bring one closer to God, as stated in the above-mentioned verse. Since, God-consciousness is the prerequisite for righteousness, great stress is placed on fasting in Islam. Thus, it is not surprising to find that when Prophet Muhammad, may the mercy and blessings of God be upon him, was asked: "Which is the best deed?" He replied, "Fasting, for there is nothing equal to it." (Al-Nasa'i) There are as many levels of fasting as there are facets to being human. Proper fasting should encompass all dimensions of human existence for it to have the divinely intended effect.
source: Dr Bilal Philips Islamic Book