The calories in a can of soda seem pretty inconsequential when you are downing one on a hot day or as you watch television. They certainly are refreshing. Even for those of us who pay attention to calorie counts on food packages, the 250 calories in a soda probably don't seem so bad, really.

But if you realize how long it will take you to walk or run those calories off, the 250 calories begin to seem quite different. A new study finds that when people know what the calories in that bottle of soda actually “cost,” they start running for water instead.

The most effective poster was the one saying it would take five miles to walk off a soda.

“People don't really understand what it means to say a typical soda has 250 calories,” study leader Sara N. Bleich said in a news release. “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.”

She and her team put one of four small posters up in convenience stores in predominantly black Baltimore neighborhoods. One poster said that each bottle contained 250 calories; another that the soda had 16 teaspoons of sugar; another that it would take 50 minutes of running to work off those calories; and the last said it would take five miles to walk off the calories in the soda.

The team tracked the purchases of almost 3,100 people between the ages of 12 and 18 before and after the signs were put up. Before the posters, 98% of purchases were sodas; and after, soda purchases fell to 89%. Water purchases rose from 1% to 4%. And the purchases of large-size drinks — over 16 oz. — fell from 54% to 37%.

The most effective poster was the one saying it would take five miles to walk off a soda.

Polling some of the participants as they left the stores, the team learned that about 35% had seen the signs. And of these, 59% said they believed the information on them, and 40% said that they’d made a different drink choice as a result.

“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 says.

“Black adolescents are one of the groups at highest risk for obesity and one of the largest consumers of sugary beverages. And there is a strong scientific link between consumption of sugary beverages and obesity. Using these easy-to-understand and easy-to-install signs may help promote obesity prevention or weight loss.”

The signs will likely work with other groups as well. But more research will be needed to find the most effective messages, sizes, and locations for the signs — and perhaps how the store owners feel about the signage, and whether it takes away business.

And even if signs don’t show up in stores for a while, just remembering that it takes five miles to walk off a soda — or a 50 minutes of running — will hopefully steer you away from that sugary soda, and towards a healthier choice.

The study was carried out at Johns Hopkins University and published in American Journal of Public Health.