It’s the norm for all Fridays to be meatless but the U.S. bishops have received since I believe 1965 an indult for U.S. Catholics such that only LENTEN Fridays are meatless; for the other Fridays of the year a penitential practice is highly to be recommended. I find it easiest myself to just keep all Fridays meatless, and it is very penitential for me because I loathe fish and I’ve also been very anemic much of my life, and absorb iron very poorly except from red meat sources.
Our brothers and sisters the Orthodox also have many days that are meatless, and indeed even stricter fasting. I believe some Orthodox are, or are just about, to start their Christmas fast. And their Lenten fast is very strict; no meat, no eggs, no dairy.
Why do we fast? It’s been a long, long practice. Rooted of course in Jewish history, and Jesus Himself we know fasted and prayed. We fast and abstain on Friday in commemoration of His death on the cross on that Good Friday. Christians in the early Middle Ages in Britain fasted on Wednesdays, Fridays, and Saturdays as a general rule, plus having the Advent fast from Martinmas (Nov. 11) to Christmas, Lent (Ash Wednesday to the Triduum), fasting on ember and rogation days, etc. It’s a mortification of our bodies (as St. Paul often commends), a remembrance of His suffering, a wish to join with Him, etc.
But it’s in no way a nasty kind of thing where we say that ‘flesh’ is evil, for example, or that we NEVER eat meat. We simply abstain from a GOOD thing, and offer up that abstention as a kind of gift.
It’s a type of prayer. . .a prayer of sacrifice, made voluntarily, made always with God in mind, made in thanksgiving of His gifts and voluntarily ‘refraining’ from them for a temporary period (like a Friday) as a sign that like Jesus we wish to ‘give up’ even something we like as a sign of willing obedience to the Father.
After all, Jesus’ life on earth was a good thing. He gave up that life of His willingly, even though He did not HAVE to do so, and He offered that sacrifice for us. Surely we can offer up a few sacrifices ourselves and offer them to HIM, and that’s what we do.