The Bite National Doughnut Day: The surprising origins of America's most American holiday (+video)

Shops all over the country are giving away free doughnuts on Friday in honor of National Doughnut Day. But the holiday celebrates more than just America's sweet tooth. 

Doughnut lovers, rejoice: Friday marks National Doughnut Day. America's doughnut makers are celebrating with giveaways, with Krispy Kreme giving a free doughnut to every customer, Dunkin' Donuts offering a free-doughnut-with-the-purchase-of-a-beverage deal, and smaller shops and bakeries holding promotions of their own.