Knowing how much physical activity is needed to burn off the calories in a bottle of juice or soda may deter teens from buying sugary beverages, according to a recent study.

Researchers from the John Hopkins Bloomberg School of Public Health found that adolescents who saw printed signs explaining that they would need to run for about 50 minutes to burn off the calories in a sugary drink were more likely to leave the store with a lower calorie beverage, a healthier beverage or a smaller size beverage.

And those healthier choices persisted weeks after the signs came down.

The findings add to the growing evidence suggesting that simply showing calorie counts on products and menus isn't enough to break people from their bad eating habits. With calorie counts expected on menus in chain restaurants with more than 20 outlets by early next year the Affordable Care Act, policymakers may need to rethink how that information is communicated.

"People don't really understand what it means to say a typical soda has 250 calories," Sara N. Bleich, who led the study, said in a statement. "If you're going to give people calorie information, there's probably a better way to do it. 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."

For the study, Bleich and her colleagues installed signs in six corner stores in low-income, predominately black Baltimore neighborhoods for six-week stretches between August 2012 and June 2013. The signs, four in all, presented a key fact about the number of calories in a 20 oz. bottle of soda, sports drink or fruit juice: that each bottle contained 250 calories, had 16 teaspoons of sugar, would take 50 minutes of running to work off those calories or would take five miles to walk the calories off.

The research team observed more than 3,000 drink purchases in the stores by black adolescents between the ages of 12 and 18 and interviewed 25 percent of them after leaving the store about whether they saw and understood the signs. Of the 35 percent of kids who said they saw the signs, 59 percent said they believed them and 40 percent said they changed their behavior as a result.

Overall, the number of sugary drink calories purchased went from 203 calories before the miles of walking sign to 179 after. The size of the purchases also fell from 54 percent buying more than 16 oz. to 37 percent.

"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," Bleich said.

The findings were published in the American Journal of Public Health.