As long as they have the bridegroom with them they cannot fast.But the days will come when the bridegroom is taken away from them, and then they will fast on that day.
-- Mk 2:18-22
To prepare for worthy reception of this sacrament (the Eucharist), the faithful should observe the fast required in their Church. Bodily demeanor (gestures, clothing) ought to convey the respect, solemnity, and joy of this moment when Christ becomes our guest.
-- CCC 1387