Interesting. That's not the case with US-based Catholics, or other Catholics I've met from Western or Southern Europe and the Americas. But while I know a few Eastern Orthodox folks I haven't really compared the specifics of the traditions.

Aquinas held that eggs shouldn't be eaten during Lent:

http://www.newadvent.org/summa/3147.htm

I don't know when/how the tradition changed.

I'd also add that "pancake day" (aka Shrove Tuesday) only makes sense if eggs are one of the prohibited foods: https://simple.wikipedia.org/wiki/Shrove_Tuesday

Most Catholics from those areas are Western Catholics (a.k.a. Latin Rite Catholics or Roman Catholics).

See: https://en.wikipedia.org/wiki/Catholic_particular_churches_a...