Ah, finding the compass to navigate, amidst the fog, the moral life.
I don’t remember ever having read anything authoritative, or anything that would give certain direction from the Church, on the subject. I have, however, recently read an article that bravely attempts to tackle the dilemma. The article is called “To Cheat or Not to Cheat; That Is My Question” by Tommy Tighe on a website called “Aleteia”.
The author points out that:
Catholics line up on both sides of the issue... On one side you have the folks who consider making a sacrifice for just six days of the week to be “wimping out.” They feel that you should maintain your sacrifice for the entirety of Lent if you want it to have full spiritual value.
On the other side, you have the folks who insist upon the fact that Sunday is not a penitential day. They don’t feel that fasting or abstinence have any place on the Lord’s Day and often use Matthew 9:15 as the defense for their position: “How can the guests of the Bridegroom mourn while he is with them? The time will come when the Bridegroom will be taken from them; then they will fast.”
He also dug up a statement from the website of the United States Conference of Catholic Bishops which advised:
(Our Lenten sacrifices) are disciplinary in nature and often more effective if they are continuous, i.e., kept on Sundays as well. That being said, such practices are not regulated by the Church, but by individual conscience.
So the author concludes that we are left to look into our hearts and to discern the reasons by which we are motivated. In other words, it’s up to you – but be sure you are acting in good conscience. So there. Whether feasting or fasting – be prayerful and faith-filled.