The Associated Press

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.

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

To celebrate the burger's anniversary, Delligatti, 89, and his family opened a Big Mac Museum Restaurant this week in North Huntingdon, Penn., that is full of memorabilia, celebratory exhibits and the world's largest Big Mac statue.

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 magazine.

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

"The Big Mac is certainly one of our most popular sandwiches," said spokeswoman Danya Proud. "There is only one Big Mac and there will only ever be one Big Mac."

McDonald's estimates 550 million Big Macs are sold each year in the United States. Do the math and that's about 17 a second. Weighing in at about 225 grams, with 540 calories and 29 grams of fat each, that's enough to make nutritionists cringe.

"When it was eaten once in a while, there wasn't anything wrong with it," said Marion Nestle, professor of nutrition and food studies at New York University's Steinhardt School of Culture, Education and Human Development.

Love it or hate it, the Big Mac has grown from its humble beginnings to become a cultural unifier, said pop culture expert and author Rachel Weingarten.

"You can live in Beijing or Brooklyn and you can enjoy as your favourite snack a Big Mac attack," she said.

"Maybe you didn't grow up watching the same cartoons, maybe you didn't grow up speaking the same language, maybe you grew up next door to each other and never said hello, but you suddenly have a point of reference - this warm, yummy, bad-for-you, sometimes-naughty thing."