Eastern rite Christians begin the Nativity Fast today, on November 28, this is the last fast of the year.
Fasting begins on November 28 according to the new calendar style, and ends on January 7. It lasts 40 days, and therefore in the church statute, it is also called “Great 40 Days.’
Originally, Advent lasted seven days for some Christians, while for others - a bit more. In the cathedral in 1166 when the Patriarch of Constantinople Luque and the Byzantine emperor Manuel all Christians were supposed to fast for forty days.
Advent is considered lax. You cannot eat the food of animal origin: meat, eggs and dairy products. Other limitations change depending on the weekday.
Sometimes the fast is called Philip's Fast (or the Philippian Fast), as it traditionally begins on the day following the Feast of St. Philip the Apostle.
Nativity Fast or Advent is not a strict fast but has its peculiarities.
The days of the fast differ from holidays and working days. On feast days the Church calls us to thank God and the saints for God's great works; and during the fasts, to be reconciled with God and to take part in the life, sufferings and the death of the Saviour and the saints. Feasts make us disposed to spiritual joy and hope, and fasts, to contrition and tears. On feast days, out of spiritual joy, the Church blesses hearty meals; but during fasts, it prescribes frugal ones, lenten fare.
Everything is strictly calculated to weaken carnal desires, which are excited by hearty and sweet meals. It is not designed to greatly weaken our flesh, but rather to make it light, strong, and more submissive to our spiritual will, and to preserve it vigorously to fulfill the demands of the spirit.
During fasts, we must abstain from eating meat, cheese, butter, eggs, milk and sometimes fish, according to different fasts.