During Lent, millions of Christians are encouraged to give up indulgences like sweets, alcohol, and processed food, with Catholics being expected to forgo eating meat on Fridays.

While dining at hamburger joints like McDonald’s may seem unconventional during Lent, the Filet-o-Fish offers a viable protein alternative for those observing the Lenten season.

For some cultural reasons, fish isn’t generally considered meat by religious folks in the same way pork, chicken, and beef are. Hence, it booms in popularity during Lent.

As of 2023, McDonald’s sells about 300 million Filet-o-Fish annually (per USA Today), around 75 million of which are sold during Lent. That’s over 1.8 million sandwiches per day.

Before Filet-o-Fish’s inception, McDonald’s only sold burgers and fries. Since eating fish on Fridays was a year-long practice for Catholics even back then, the business suffered.

To address this issue, Ohio McDonald’s operator, Lou Groen developed a sandwich with tartar sauce and flaky fried fish in 1962, that blew the competition out of the water.

After showing the recipe to the higher-ups at McDonald’s, Groen swapped the halibut for Atlantic cod and included a slice of American cheese, adding the Filet-o-Fish to the menu.