Calorie counts on food menus don't work. That's because they require a lot of mental math. Ambling into a Starbucks, how many customers have a solid sense of how many calories they have already consumed that day? Do they know how many more they intend to eat? Can they make a decision on how a 380-calorie grande Pumpkin Spice Latte fits into that calculus, especially considering the uncaffeinated mob of customers impatiently waiting in line behind them?

It's complicated thinking. And without the context of where that item of food fits into their daily intake, it's hard to make an on-the-spot nutrition decision. That's why earlier this year the Food and Drug Administration redesigned nutrition-fact labels for supermarket goods to make them more easily scannable.

Researchers at Johns Hopkins University recently tried to figure out whether they could add greater nutritional context to these on-the-spot purchasing decisions. In their study, published in the American Journal of Public Health, they targeted one of America's most at-risk populations when it comes to health and nutrition: black teens. As a group, black teens consume twice the recommended amount of sugary drinks for their age group. These dietary habits have long-term consequences, as African-Americans contract diabetes at a rate nearly double that of white Americans. Thirty-five percent of black children age 2 to 19 are overweight or obese (compared with 30.1 percent of all children 2-19 who are obese).

The scientists staged their experiment at six convenience stores in predominantly black Baltimore neighborhoods. In the soda section of the stores, the neighborhood teens saw on display one of the following four messages:

 

+ (American Journal of Public Health)

The researchers recorded four weeks' worth of purchasing data (for a total of 4,516 purchases), and then compared that data with a baseline period during which no signs were hung in stores.

So what worked?

"Our results showed that providing information in the form of miles of walking to burn off a 20 ounce bottle of soda or fruit juice had a modest, but significant, effect on reducing the number of calories compared with other relative information in the form of minutes of running or teaspoons of sugar," the researchers state in their conclusion. The teens made significantly fewer soda and sports-drink purchases, more water purchases, and more purchases that didn't include any beverage at all. So the kids were either making a healthier decision, or opting out of buying a soda when they saw the sign.

While the walking sign was most effective, across all the interventions, average calories purchased fell from 149 calories during the baseline period to 121 calories during the period the signs were posted. And the effect persisted to a significant degree even six weeks after the signs were removed from the stores.

Numbers without context are just that—numbers. To show how those numbers translate into our lives is an entirely different task, but potentially much more useful.

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