From the beginnings of Christianity, both the Western and Eastern Churches observed Fridays as a special fast day in observance of the ultimate sacrifice Christ made for us on Good Friday. For some this meant giving up meat, and for others it meant giving up meat plus any dairy products.
Why is fasting important? The apostles and our forefathers knew that in order to say yes to Jesus, we have to practice saying no to ourselves. Fasting helps us to deny ourselves and keeps us from making pleasure, honor and glory the center of our thoughts instead of Christ and His will for us.