The Nativity Fast is a period of abstinence in preparation for the Nativity of Jesus, (December 25). The Eastern fast runs for 40 days and thematically focuses on proclamation and glorification of the Incarnation of God. The fast is observed from November 15 to December 24. For the faithful, it is a time to purify both soul and body to enter properly into and partake of the great spiritual reality of Christ’s Coming, much like the preparation for the fast of the Lord’s Resurrection.
Through the discipline of fasting, practiced with humility and repentance, it is believed that by learning to temper the body’s primary desire for food, that other worldly desires can be more easily tempered as well. Through this practice one is better enabled to draw closer to God in the hope of becoming more Christ-like. While the fast influences the body, it is important to note that emphasis is placed on the spiritual facet of the fast rather than mere physical deprivation. Orthodox theology sees a synthesis between the body and the soul, so what happens to one affects the other. The church teaches that it is not enough to fast from food; one must also fast from anger, greed and covetousness. In addition to fasting, almsgiving is also emphasized.
In the Eastern Orthodox Church, the fast traditionally entails fasting from red meat, poultry, meat products, eggs, dairy products, fish, oil, and wine. Fish, wine and oil are allowed on Saturdays and Sundays, and oil and wine are allowed on Tuesdays and Thursdays.
The fasting rules permit fish, and/or wine and oil on certain feast days that occur during the course of the fast: Evangelist Matthew (November 16), Apostle Andrew (November 30), Great-martyr Barbara (December 4), St. Nicholas (December 6), St. Spiridon and St. Herman (December 12), St. Ignatius (December 20), etc. The Nativity Fast is not as severe as Great Lent or the Dormition Fast.
As is always the case with Orthodox fasting rules, persons who are ill, the very young or elderly, and nursing mothers are exempt from fasting. Each individual is expected to confer with their confessor regarding any exemptions from the fasting rules, but should never place themselves in physical danger.
There has been some ambiguity about the restriction of fish, whether it means the allowance of invertebrate fish or all fish. Often, even on days when fish is not allowed, shellfish may be consumed. More detailed guidelines vary by jurisdiction.