CHICAGO — Normally, a 40-year-old sandwich would be something to be avoided.

CHICAGO — Normally, a 40-year-old sandwich would be something to be avoided.

Unless you're one of millions who flock to McDonald's each year to chow down on a Big Mac. The triple-decker burger, which helped breed America's super-size culture and restaurants' ever-expanding jumbo meals, is turning 40.

For some fast-food junkies, that's cause for celebration.

"The flavors that come together — it's like heaven in your mouth," said April Kohlhaas, a 31-year-old Chicago resident. "It's just tradition, like American comfort food."

The Big Mac was first introduced in 1967 by Jim Delligatti, a McDonald's franchise owner in Uniontown, Pa. A year later, it became a staple of McDonald's menus nationwide.

Indeed, the sandwich has become a veritable pop culture phenomenon, spawning everything from an impossible-to-forget jingle ("Two all-beef patties, special sauce, lettuce, cheese, pickles, onions on a sesame-seed bun," anyone?) to a currency-evaluation index created by The Economist.

Along the way, more people in more than 100 countries have given in to Big Mac attacks, according to Oak Brook-based McDonald's Corp.

McDonald's estimates 550 million Big Macs are sold each year in the U.S. alone.