Here is a famous finding from social psychology. If you want to encourage people to get vaccinated against some disease, it helps to educate them about the benefits of vaccination. But you’ll have a much bigger impact if you give people a map, showing them exactly where to go to get a shot.

Elementary though it is, this finding is important, because it demonstrates that when people don’t respond to a suggestion, it may be because they need some help in identifying the specific steps they are being asked to take. People pay a lot more attention if they are given something like a map.

In its efforts to promote healthy eating, SmartReceipt Inc. is taking this idea seriously. The company’s Nutricate receipt provides people with the standard information about the meal they just bought, but with a few significant twists. The receipt contains a panel with personalized information about the total calories, fats, carbohydrates and protein in the particular foods customers chose.

You also receive some simple “Did you know?” messages, specifically tailored to your own choices. You might read, “Holding the mayo on your sandwich will save you 150 calories and 10 grams of fat,” or “Low-fat milk is a great source of calcium, and you just had over 35 percent of your daily calcium requirement.”

To be sure, the Nutricate receipt isn’t likely to prove appealing to all people and all restaurants. Some customers might find it intrusive or annoying. But other customers, and many restaurants, would undoubtedly find it useful. A big question is: Will people pay any attention to it?

Restaurant Choices

Kelly Bedard and Peter Kuhn, economists at the University of California at Santa Barbara, have just answered that question. Their report, issued this month, explores the implementation of Nutricate at Burgerville, a restaurant chain in the Pacific Northwest. The study spans a period of more than two years (125 weeks) and involves sales data from 39 Burgervilles.

Bedard and Kuhn found that the Nutricate receipt significantly changed people’s choices. Responding to the most frequent suggestions on the receipt, Burgerville’s customers became more likely to purchase kids’ meals with apples instead of fries, to select breakfast sandwiches without sausages, and to request main-course items without cheese or sauce. The Nutricate receipt also produced a 2.1 percent reduction in the average amount of cholesterol per transaction.

Bedard and Kuhn found that a lot of customers used their personalized ordering suggestions when they returned to Burgerville restaurants. They found no evidence that use of the Nutricate receipt reduced total sales.

Why does Nutricate work? One reason might be salience. Every day, people receive a lot of information, and the receipt makes certain recent choices, and healthier options, more salient than they would otherwise be.

Bedard and Kuhn prefer another explanation, which is that the Nutricate receipts combine personally relevant information with specific suggestions for action. In these respects, the receipts belong in the same family with recommendations from Netflix Inc. and Amazon.com Inc., which similarly offer personalized suggestions, based directly on people’s past choices.

Of course Netflix and Amazon try to track people’s preferences, not to alter them in any way. But because Nutricate offers pretty modest suggestions (“hold the mayo”), it is essentially providing a personalized map, which people are free to disregard if they like.

We shouldn’t exaggerate the study’s findings. Bedard and Kuhn find no statistically significant effect on total calories per transaction, apparently because customers ended up purchasing more high-calorie main dishes.

Potential Benefits

Nonetheless, the movements in the direction of healthier items (such as grilled chicken for fried chicken and frozen yogurt for ice cream) and the long-lasting reduction in cholesterol per transaction suggest that the approach has real potential.

When we get lost on the highway, we can consult a GPS, which tells us how to get from where we are to where we want to go. The Nutricate receipt isn’t exactly a GPS, but it offers a valuable lesson for this holiday season: Modern technologies are going to make it increasingly easy for consumers to obtain simple, personalized information, and to use that information to make better choices in the future.

(Cass R. Sunstein, the Robert Walmsley University professor at Harvard Law School, is a Bloomberg View columnist. He is a former administrator of the White House Office of Information and Regulatory Affairs, the co-author of “Nudge” and author of “Simpler: The Future of Government.”)

To contact the writer of this article: Cass R. Sunstein at csunstei@law.harvard.edu.

To contact the editor responsible for this article: Katy Roberts at kroberts29@bloomberg.net.