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Does calorie information help consumers make healthier choices? Not always. But a new study finds that when calorie counts are presented in an easily understandable way, even teenagers — those experts in never listening to useful advice — can be persuaded to avoid high-sugar choices.

For the new study, published in the American Journal of Public Health, researchers from the Johns Hopkins Bloomberg School of Public Health went to corner stores in predominantly black neighborhoods of Baltimore and posted signs showing calorie information about sugary drinks (sodas, fruit drinks, energy drinks) on refrigerated beverage cases.

The researchers tested three different signs, each brightly colored, in four corner stores. One sign said that a bottle of soda or fruit drink had 250 calories. Another noted that each bottle contained 10% of a person’s recommended daily calorie intake. A third sign informed consumers that they would have to run for 50 minutes to burn off the calories in a single sugary drink.

The researchers collected data for 1,600 beverage purchases by black teens — who tend to drink more sugary beverages and to be obese — including 400 sales during a no-sign baseline period, and 400 for each of the three signs.

Overall, they found, teens were 40% less likely to buy a sugary drink after seeing any of the posted calorie counts than when they were given no information. They were even less inclined to buy a soda or a fruit drink after viewing the sign that presented the exercise equivalent, which reduced soft drink purchases by 50%.

The study did not track exactly which drinks teens substituted for the sugary ones, but the data suggest they may have tended toward some non-calorie options: while beverages like bottled water and diet soda made up only 6.7% of drink sales before the signs appeared, that percentage increased to nearly 14% after the calorie information was posted.

Previous studies on calorie counts and buying behavior have been conflicting. One study in July of fast food customers in New York City showed that posting calorie information on above-the-counter menus did little to reduce the number of calories people ordered. Also, reported Healthland’s Tara Thean at the time:

A 2009 study by NYU and Yale professors found, after checking receipts, that customers actually ordered slightly more calories than the typical customer had before the calorie count law was implemented. Two years later, an NYU School of Medicine study demonstrated that calorie labeling did not change the number of calories teenagers and parents purchased at fast food chains in the city, with teens buying a whopping 725 calories on average even after the labeling. And another analysis of one Taco Time outlet in Washington State found “basically absolutely nothing” in purchasing changes after calorie counts started popping up.

The failures may have to do with how the information was presented. Calorie information works best when it is displayed clearly and visibly alongside the items and prices listed on menus, not tucked away where it can’t easily be seen. But even then, it may not matter if consumers don’t know how to interpret it — if they don’t know, for instance, how many calories they’re supposed to eat in a day. That may help explain why so many teens tended to heed the Baltimore store posters. Not only were they easily visible, but they also helped put calorie information in context.

“This study showed that black teenagers will use calorie information, especially when presented in an easy-to-understand format, such as a physical activity equivalent, to make healthier choices when it comes to buying a drink at the local corner store,” lead researcher Sara Bleich, an assistant professor at the Johns Hopkins Bloomberg School of Public Health, said in a statement. “Most consumers underestimate the number of calories in a can of soda, and they often do not realize that such calories can add up quickly.”

With American teenagers consuming an average 300 calories per day from sugary drinks alone — a significant contributing factor to children’s overweight and obesity rates — adding calorie-information posters could help.

Meredith Melnick is a reporter at TIME. Find her on Twitter at @MeredithCM. You can also continue the discussion on TIME’s Facebook page and on Twitter at @TIME.