I’ve heard some people fast on Wednesdays and Fridays. Why Wednesdays?
The Betrayal of Our Lord, is why sometimes we fast on Wednesdays. Wednesday, is traditionally when the Sun and Moon were created.
Holy Mary, Mother of God. Pray for Us!
All Apostolic Christians used to fast on Wednesday. It was a rejection of the Tuesday & Thursday fast of the Jews. Later on other reasons were attributed as to the why, such as the answer given in the post above.