A message on sugar-laden soft drinks explaining just how much running or walking it would take to burn of the calories they contain could convince people to choose a low-calorie alternative, researchers suggest.

When children and teenagers were given such information they tended to purchase smaller-sized soft drinks or chose not to buy it altogether, a study found.

Analyzing some 3,000 drinks bought by children age 7 to 18 in Baltimore, Md., neighborhoods, researchers found 98 percent of them were of the sugary variety.

However, when the researchers erected colorful signs containing calorie information -- and how much exercise would be needed to burn those calories -- that dropped to 89 percent, they reported in the American Journal of Public Health.

"People don't really understand what it means to say a typical soda has 250 calories," says study leader Sara N. Bleich of the Johns Hopkins University Bloomberg School of Public Health.

"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 says.

The signs placed at six neighborhoods stores carried the information that each bottle of sugary soda had 250 calories and 16 teaspoons of sugar and that it would require a run of 50 minutes or a walk of 5 miles to work off those calories.

When the signs were displayed the size of purchases decreased, the researchers found, from 54 percent buying 16 ounces or more to 37 percent.

In addition, the percentage of children and teenagers who chose to buy no beverage at all rose from 27 percent to 33 percent.

Sodas and energy drinks with high levels of sugars and sweeteners are considered a significant factor in public health problems such as obesity that affect children and adolescents, the researchers point out.

The problem is particularly prevalent in low-income communities, where consumption of sugar-laden drinks can account for as much as 15 percent of the caloric intake in adolescents, they explain.

Black adolescents, one of the largest consumers of sugary beverages, are one of the groups at highest risk for obesity, they note.

That's why the impact of the caloric information provided and its effect of drink purchases is encouraging, Bleich says.

"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 [the signs] are removed," she says.