Fasting on Christmas Eve
Notes on the Observance of fasting during Dec 24-25
Christmas Eve is traditionally called Paramony (Greek: παραμονή).
Christmas Eve is observed as a strict fast day, on which those faithful who are physically able to, refrain from food until the first star is observed in the evening, when a meal with wine and oil may be taken.
On this day the Royal Hours are celebrated in the morning.
On the same day we also serve the Vesperal Divine Liturgy of St. Basil which combines Vespers with the Divine Liturgy. During the Vespers, several Old Testament lections ("parables") which prefigure or prophesy the Incarnation of Christ are read, and special antiphons are chanted.
Even if we celebrate the Vesperal Liturgy in the evening one still has to be prepared for Communion like for a regular Sunday Liturgy by prayer, regular Confession and fasting (refrain from food and drink from the night before or if not able too at least from noon on Christmas Eve)
The Lenten fast continues even after the Vesperal Liturgy on Nativity Eve, until the end of the Liturgy the next morning.
The Orthodox do not normally serve a Midnight Mass on Christmas Eve; rather, the Divine Liturgy for the Nativity of Christ is celebrated the next morning.
After the Liturgy we break the fast and we observe a fast free period until January 4.