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 7th. 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 week day.