Not eating is a way of glorifying God just as much as feasting can be. This also provides an interesting symmetry where the Fall, caused by eating, is reversed through fasting. Fasting is necessary for feasting to have meaning; if we feast every day, then feasting no longer celebrates the Lord.
There are two types of fasts in our Church. The first type of fast is a total fast, where we abstain from food and drink entirely. This type of fast is most familiar to us on Sundays, where we fast before receiving the Eucharist. The second type of fast is an “ascetical fast,” where we refrain from eating certain foods. In the Byzantine tradition, the foods forewent usually include meat, fish, dairy, oil, and wine. While a total fast can only be observed for short periods, ascetical fasting can be maintained over longer periods of time. Monks, for instance, often perpetually fast from meat. The purpose of ascetical fasting is to teach us that we are not bound to certain foods but to Christ alone, who sustains us.
In our tradition, we fast on every Wednesday and Friday (except for the weeks immediately following Pascha, Christmas, Theophany, the Sunday of the Pharisee and the Publican, and Pentecost--fasting is forbidden on these days), the Great Fast (the 40 days before Holy Week), the Christmas Fast (November 15 til December 24), the Fast of the Theotokos (August 1 to August 14), and the Fast of Peter and Paul (All Saints Sunday to June 28).
Three suggested “levels” of fasting are as follows:
Beginning: On Wednesday and Friday do not eat any meat, and increase the amount of prayer one does throughout the day. During fasting periods, attend at least one service a week.
Intermediate: On fasting days, do not eat anything before noon and no meat whatsoever. Keep additional fasting days throughout fasting seasons. During the Great Fast, abstain from dairy products as well. Attend two Lenten services a week.
Advanced: In addition to the intermediate level, keep each day in fasting seasons as a fasting day. Attend all services. Replace entertainment with spiritual reading and acts of sharing.
Fasting is counterproductive to spiritual growth unless one also participates in prayer and almsgiving. Increasing your religious activity can take the form of attending services more frequently, reading, using religious video or audio, or devoting time to charitable concerns.