“Did you know that working off a bottle of soda or fruit juice takes about 50 minutes of running?” If you saw a sign saying that on the vending machine or a convenience store cooler, would you still buy the drink?

According to a new study from the Johns Hopkins University Bloomberg School of Public Health, teens were less likely to buy sugary drinks after seeing such signs signs–saying how far they’d have to walk to burn off the calories.

Results published online Oct. 16 in the American Journal of Public Health showed teens chose healthier options, bought lower calorie drinks or opted for a smaller size of the sugary beverage after seeing the signs.

The impact was lasting. The teens continued to make healthy choices during the six weeks purchases were monitored after the signs were removed.

“This is a very low-cost way to get children old enough to make their own purchases to drink fewer sugar-sweetened beverages and they appear to be effective even after they are removed,” lead researcher Sara N. Bleich said in a press release.

The signs were installed in six corner stores located in predominantly black, low-income Baltimore neighborhoods.

On colorful 8.5 by 11 inch paper, each sign was displayed for two weeks in each store between August 2012 and June 2013. There were four signs in all, each with a key fact about the calories in a 20 ounce bottle of soda, sports drink or fruit juice:

(1) “Did you know that a bottle of soda or fruit juice has about 250 calories?”

(2) “Did you know that a bottle of soda or fruit juice has about 16 teaspoons of sugar?”

(3) “Did you know that working off a bottle of soda or fruit juice takes about 50 minutes of running?”

(4)“Did you know that working off a bottle of soda or fruit juice takes about 5 miles of walking?

Researchers recorded 3,098 drink purchases by black teens – a group at high risk for obesity – who appeared to be between 12 and 18 years of age. They asked a quarter of the teens as they were leaving the store whether they saw and understood the signs. Only 35 percent said they saw the signs. Of those, 59 percent said they believed them and 40 percent changed their drink choice as a result.

Sugary drinks made up 97 percent of the beverage purchases in the stores before the signs went up and 89 percent after they went down. Regardless of which sign teens saw, the number that chose not to buy any drink rose from 27 to 33 percent during the period of the study. Water purchases jumped from one to four percent.

Adolescent beverage purchases averaged 149 calories before the signs went up and fell to 121 calories on average no matter what sign they were shown.

The most effective sign was the one that warned shoppers they’d have to walk five miles to burn off the drink.

The results suggest that doing the calorie/exercise equation for consumers could motivate people to improve their eating habits more than simply displaying calorie content on food labels.

Under Obamacare, chain restaurants with more than 20 locations have to put calorie information on their menus. “People don’t really understand what it means to say a typical soda has 250 calories,” Bleich said. “What our research found is that when you explain calories in an easily understandable way such as how many miles of walking needed to burn them off, you can encourage behavior change.”

A few caveats: the study was limited to one socio-economic demographic in one city and included only six corner stores. It’s also possible that teens who visited the stores did so more than once.