...must we give up our Thanksgiving Dinner?
{This is from a Question and Answer session in my church's monthly bulletin, answered by Fr. George Lardas.}
A: No, we need not. During the Nativity Fast (Advent), which begins 40 days before Christmas (28 November), we abstain from meat, eggs, and dairy products. On Wednesdays and Fridays we also abstain from fish, wine (spirits), and oil. Two weeks before our Christmas, after Ss. Spyridon and Herman (25 December, American Christmas), the fast becomes stricter, and fish is not permitted, and wine and oil are permitted only on Saturdays and Sundays.
It is more important to obey the rules of the Church than to follow local custom, but we may adapt our celebration accordingly. Although Thanksgiving falls on the first day of the Nativity Fast (Advent), it is also preceded by a regular fast day, Wednesday. So the latest non-fasting day before Christmas is the Tuesday before Thanksgiving, 26 November. If we wish to have the Thanksgiving dinner on the day itself, we can adapt the menu: Instead of stuffed turkey we can have stuffed salmon or other large fish. Instead of milk and butter in the potatoes and yams, we can use soymilk and margarine. Many recipies can be made for fasting.
Since Thanksgiving is always followed by a fast day (Friday) it is never right to eat the turkey leftovers the day after Thanksgiving. Sometimes the fast begins on the Friday or Saturday after Thanksgiving, so there is no non-fasting day afterward. In that case all the meat must be eaten on Thanksgiving, or discarded, or given away, or frozen until Christmas.