(CNN)– Imagine you’re choosing between two different boxes of cookies at the grocery store. One has a label informing you that you could burn off the calories in a serving by jogging for 10 minutes, while the label on the other box says you would have to jog for 20 minutes. Would that help you decide which cookie to buy?

Although the idea of these types of food labels has not really picked up steam in the United States, the Royal Society for Public Health, an organization of health care professionals in the United Kingdom, is advocating these “activity equivalent” labels. They would tell consumers how many minutes they would have to engage in several types of exercise, such as walking and jogging, to expend the calories in specific food items.

“The aim is to prompt people to be more mindful of the energy they consume and how these calories relate to activities in their everyday lives, to encourage them to be more physically active,” wrote Shirley Cramer, chief executive of the Royal Society for Public Health, in an opinion article published on Wednesday in The BMJ.

It is an intriguing idea, according to experts in the United States, but there isn’t enough information about whether these labels do any good to recommend them, much less require them by law, they said. Some even worry the activity labels could have unintended effects.

“I think it’s a good idea, but I’m a believer in evidence-based policy, so we need a fair bit more evidence before we would have a good justification for moving to a law” requiring food makers to include this label on products, said James F. Sallis, professor of family and preventive medicine at University of California-San Diego.

The evidence out there

There has not been a lot of research on the effect of physical activity labels, but the studies that are out there are somewhat encouraging. One study asked more than 800 parents to look at a fast food menu online and pick which meal they would order for their child. Parents who viewed a menu that listed calories and the number of minutes or miles to walk to burn them off did not order a lower calorie meal than those who saw only calories listed. Nevertheless, parents said they would be more likely to encourage their child to exercise if they saw information about physical activity on menus.

But it’s unclear from this study whether these labels would translate to more parents talking with their kids about exercise and more kids exercising. “There is a big gap between intention and follow-through, so it is hard to say,” said Sallis, who studies the effects of the environment on levels of physical activity.

More research needs to be done to see whether these labels affect what people buy in the grocery store and order in restaurants, and also how much they exercise, Sallis said.

Another study suggested that displaying information about exercise in a store could influence shoppers’ choices. The researchers put bright signs on beverage cases in corner stores in predominantly black Baltimore neighborhoods. They found that teens bought fewer bottles of soda or fruit juice if the sign said they would have to run for 50 minutes to burn off the calories in one of those drinks. In contrast, signs that simply stated the number of calories in a sugar-sweetened beverage, along with the percentage of total daily calories, had a smaller effect.

A similar effort was rolled out in New York City in 2011, when signs on the subway alerted riders that they would have to walk 3 miles to burn off the calories in a 20-ounce soda. Health officials there said the information helped people understand how many calories were in a sugary drink.

Although a simple label — saying, for example, that it would take 45 minutes to walk off that cookie — would be easy for consumers to understand, it could also be misleading. “It will take someone who is 100 pounds twice as long to walk it off as a 200-pound person, so in fact, if there was a little more information, which of course it would be hard to put on the label, it might be more encouraging to tell people if you are already overweight it might take you less time to walk that off,” Sallis said.

Potential unintended consequences

According to Sara Haas, a spokeswoman for the Academy of Nutrition and Dietetics, “it is a nice idea in theory because some people have said it made them feel motivated when making choices” to know how much they would have to exercise.

And Haas thinks these labels may influence people to buy lower-calorie food — a good thing, if those foods are also lower in sodium and healthier overall. But she doubts they would really motivate people to exercise more.

At the same time, Haas worries that the labels could lead people to take an even more calorie-centric view of food. If you see that you would have to run 5 miles to expend the calories in a bag of jelly beans, “it gives you a pass,” Haas said. You might even think that those jelly beans are just as good a choice as a fruit salad or bowl of cereal, if those foods also contained the caloric equivalent of a 5-mile run. “(But) jelly beans don’t hold any nutritional value, and a fruit salad has vitamins and minerals and antioxidants and all these things that are going to help your body run efficiently,” Haas said.

A more useful tool for consumers will probably be the updated nutrition facts panel, Haas said. The U.S. Food and Drug Administration is currently working to redesign these labels on packaged foods in a way that is more user-friendly and highlights the level of components that you should avoid or that are good for you in the food item.

“There is a lot of process that has to happen before anything ends up on our food packaging, and right now they’re focusing on the nutrition facts panel to make them more meaningful,” Haas said.

Other ways to label foods

Instead of adding a label about exercise to food packages, it might be more useful to post that kind of information where people shop, such as in the study of Baltimore corner stores, Haas said. But to really get an idea of how much you need to work out to burn off those late-afternoon cookies, Haas encourages people to talk with a registered dietitian. He or she will take into consideration the foods you consume and help guide you in figuring out the level of physical activity you should be aiming for, she said.

A law requiring chain restaurants in the United States to list the calorie content of their menu items went into effect in December. Some studies have suggested calorie labeling on menus does not lead consumers to order lower-calorie items, but could motivate restaurants to reformulate their dishes to contain fewer calories.

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