Thanks to the rise of food delivery services like Grubhub and Eat24, it's getting easier to order meals online.

And when the Food and Drug Administration's new calorie labeling regulations go into effect next spring, it'll also be easier to see exactly how many calories we're ordering with each click. Some companies like Starbucks and Panera already offer up calorie counts on their online menus.

But will knowing the calorie count have any effect on whether you add the hamburger or hummus wrap to your cart?

A new study from researchers at Carnegie Mellon University and the University of Pennsylvania suggests the answer is yes.

"Calorie labels can be really helpful," explains lead author Eric VanEpps. "We have what we think of as healthy categories like salad. But not every salad is healthier than every sandwich."

VanEpps, then a graduate student at Carnegie Mellon, wanted to know whether people would make more healthful online food choices if they had information about the calories in each menu item.

He already knew that in some restaurant settings, people made better choices when "traffic light" color-coded labels helped them distinguish between healthful (green), less healthful (yellow) and not-so-healthful (red) meals.

He wondered whether the same would be true for people placing online orders.

To find out, VanEpps and his team worked with a large health insurance company in Louisville, Ky., to create a new online lunch-ordering system for employees. Over the course of the six-week study, people could select food on a website and then pick it up, skipping the line at the office cafeteria. Each of the nearly 250 website users saw online menus with either "traffic light" coding, exact calorie counts, both food label types, or no labels.

It turned out that employees who saw online menus with any indication of a meal's caloric content — either the exact calorie counts or the more indirect traffic light coding — ordered about 10 percent fewer calories than people who didn't have access to health information.

Brenna Ellison, a food economist at the University of Illinois, Urbana-Champaign, conducted a similar study in a restaurant setting. Unlike VanEpps, she found that traffic light labels could help people make more healthful choices, but actual calorie counts had little influence.

"I do think this new study is an improvement on our knowledge, which is great," she says. "Maybe when people [ordering online] have the time to sit down and think about it, they are attentive to the calorie information."

Dr. Anne Thorndike, a primary care and cardiovascular disease specialist at Harvard Medical School who has also studied the "traffic light" system, says that dropping 10 percent of your lunchtime calories on the occasions that you happen to eat from the office cafeteria isn't likely to improve your overall health.

"But," she adds, "if you start also seeing these labels in restaurants, and cafeterias, and your local supermarket, if as a society it becomes more of a cultural change, then yes, we'd see health benefits."

Do people really want to know how many calories come with their online orders? Richard Banfield, CEO of a Boston-based digital product design company, says that he certainly does. Banfield regularly orders from Starbucks online. He first noticed calorie counts on the in-store menu and then saw them pop up on his phone. The result: no more Frappuccinos for him.

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