Sara Bleich, an associate professor of public health at Johns Hopkins University, found that only 30 percent of patrons even noticed calorie listings in restaurants. And in a 2013 study in the American Journal of Public Health, researchers at two New York City McDonald's locations handed some customers pieces of paper with recommendations for how many calories they should eat per meal or throughout a day. But customers with this information did not eat fewer calories than those given nothing.

This isn't entirely surprising. Obviously, not everyone who eats at large chain restaurants is making a conscious effort to eat well. And even those who wish to make healthy choices sometimes lack an understanding of what, say, "1,000 calories" means. A study at the Johns Hopkins School of Public Health found that restaurant customers in Baltimore made little attempt to eat healthily when shown calorie listings. But when food calories were matched with an equivalent amount of exercise, they made more of an attempt to eat less.

Should restaurants just abandon calorie listings altogether? There is evidence that, in the aggregate, including the information produces positive outcomes. Researchers at Stanford found that Starbucks locations listing calories on their menu experienced a 6 percent reduction in total calories consumed per transaction. A study has also found that companies that list calories have introduced healthier items to their menus.

Extensive calorie listings alone won't curb obesity. But that doesn't mean arming customers with more information—even if some of them don't even notice it—is a waste of time.

"When it comes to human food choice, no one would expect that this strategy would work for everyone," says Madelyn Fernstrom, health editor of NBC News. "But it certainly can’t hurt."

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