At one time Lenten abstinence from meat was much stricter than it is today. In the past, Catholics did fast from meat byproducts as well as from meat. That is why there arose in some areas in the West the tradition of Fat Tuesday, the day that preceded the opening of Lent on Ash Wednesday. Catholics would clean out their pantries of meat byproducts by using them in special meals on that Tuesday before Lent. Even today in England, there is a tradition of pancake races on Fat Tuesday in honor of the one-time custom of making pancakes on this day to use up milk, eggs, and butter.
Such Lenten abstinence from meat byproducts is no longer required for Latin-rite Catholics, although it is still mandatory in Eastern churches that are in union with Rome.