Why do the bride and groom fast on their wedding day?

Since on the day of one's wedding G-d forgives the bride and groom of all their previous transgressions, it is seen as a private Yom Kippur for the couple. They fast until the ceremony, add Yom Kippur confessions to their afternoon prayers, recite the Book of Psalms, and ask for forgiveness for the wrongdoings of their youth, committed knowingly or unknowingly, before starting their new life together.