Well, Ash Wednesday and Fridays during lent.
The Orthodox include eggs, oil, butter, etc in the prohibited foods during lent. The Catholic Church included these in the prohibited food categories centuries ago, but has loosened the restricitions. That however does not exempt one from moderation at the table during lent, nor either giving something up, or doing some extra charitable acts during the season. Advent is also treated like a “Mini” Lent, and should be observed in the same basic manner in order to prepare our souls for the coming of our Lord.