Oh, That Hamburger Is 900 Calories? Yes, Please

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Let's say you're in a fast-food restaurant, and you're informed that the hamburger you're about to order has 900 calories. Will that knowledge influence your decision to order something with fewer calories?

Dan Ariely, professor of psychology and behavioral economics at Duke University and author of The Upside of Irrationality, says most likely not. You'll probably stick with that hamburger.

"You would expect that the moment you give people information ... people would stop consuming high-caloric stuff," Ariely tells NPR's Robert Siegel. "But the reality is that the evidence is just not there."

Ariely cites studies conducted in New York City after the city passed legislation forcing fast-food restaurants to post caloric information for consumers to see. The studies looked at the effect the information had on fast-food consumption.

"They saw no effect," he says. "In one study, it actually went the other way around. People said, 'Hey, only 800 calories! Give me fries with that.' "

Ariely says Duke University also conducted a similar study. He says they posted caloric labels at "the Duke version of Panda Express," a fast-food version of Chinese food. And they saw "absolutely no difference" in caloric consumption.

But then they took it a step further and said: "What else could we do? What other inventions?"

People eat everything you give them. But if you give people a mechanism to limit what they're going to have for food later on, people actually eat less as a consequence.

They decided to give people an option of receiving less of the main dish -- for example, the orange chicken. People said, "No," according to Ariely. So then they asked people if they wanted less of the side dish. They asked people, "What about we give you half a portion of fries -- that would save you 250 calories. Are you interested in that?" Ariely says that more than 40 percent of the people said, "Yes."

"What happened in eating is that no matter how much people give you to eat, you'll eat the whole thing," Ariely says. "So it's really a question of how much you start with. Because we've also tested this -- we looked at what people end up with and how much they throw away. People eat everything you give them. But if you give people a mechanism to limit what they're going to have for food later on, people actually eat less as a consequence."

Ariely concludes that offering a smaller portion of the "secondary event" is more successful than trying to reduce the "main event."

"It cuts calories and lets people execute something that's good for them," he says.

But Ariely noticed something surprising. When they stopped the promotion and studied what happened the next day, they found that people did not keep asking for it. They did not say, "Hey, I was here yesterday, they offered me a half a portion of fries, can I do it again?"

"When you offer it [to] people, they understand it's a good offer and they cut down on the calories," Ariely says. "But when you don't offer it to people, they're not doing it for their own self. So we have to think about not just what information we give to people, but how we get them to think about different paths of saving caloric consumption."