Burgers are making big bucks these days. As the New York Post reports, fast-food chains McDonald's, Burger King, and Wendy's each saw same-store sales increases of more than three percent this quarter. While that may not sound like a whopper of an increase—excuse the pun—it actually is when you compare it to the U.S. economy which, as a whole, only rose by a slim 2.6 percent in the latest quarter.

In fact, the Post reports, the U.S. economy hasn't jumped by more than three percent a year in the last 10 years. By comparison, the burger business is seriously booming. McDonald's and Burger King enjoyed same-store sales of 3.9 percent this recent quarter, while Wendy's reported a 3.2 percent same-store sales jump.

So what's behind the spike in these three chains' sales? Industry experts who spoke to the newspaper say diners are choosing fast-food options now more than ever.

"When people spend less at higher-priced restaurants and more [money] at fast food, it means they are spending their money more cautiously," Mark Kalinowski, a Nomura Instinet analyst, told the Post. But, "on the whole, the restaurant industry is going through hard times," he added, a statement that seems to contradict another recent report that showed jobs throughout the restaurant industry are on the uptick.

The food and beverage industry regularly gives the U.S. economy a boost. Take the beer industry, for example: a June 2015 report shows the beer industry accounts for nearly $253 billion in economic activity—plus it provides 1.75 million jobs and contributes $48.5 billion in tax revenue to the country. Pizza also contributes to the GDP: a June report revealed that 41 million Americans eat a slice on any given day. According to the report, that's enough in sales to make the pizza industry a top 100 country in the world based on GDP.