In the last several years, Panera, Jamba Juice, McDonald's, Chick-fil-A and Starbucks started voluntarily posting calorie information. Menu items at these restaurants were lower in calories, on average, than at 61 large U.S. chain restaurants that did not post calories in 2012, 2013 and 2014, the study found.
The average food item at chains that post calories in 2014 had 373 calories. At competitor chains, it was 521 calories.
But does posting calorie counts motivate chains to reduce the calories in menu items? Probably not, the study's authors said. Instead, they surmised that those chains were motivated to post because they already had lower-calorie menus than their competitors.
"What (chains) might be saying is, 'We are pretty good compared with our competitors, so we should publicize this,' " said Dr. Jason P. Block, an assistant professor in the Department of Population Medicine at Harvard Medical School, who led the study.
"There seems to be a growing demand for healthier food in general, and restaurants are responding to that."
The researchers used data from MenuStat
, created by the New York City Department of Health and Mental Hygiene, which has been gathering nutritional information from national restaurant chains every year since 2012. The study was published Monday in the journal Health Affairs.
Chick-fil-A said that it did not reduce calories in its menu items because it decided to start posting them. "We have always been focused on providing a wide variety of menu options our customers can feel good about ordering and eating. ... We added calorie counts to our menu boards because it was the right thing to do. Chick-fil-A believes in making it easier for our guests to make informed choices," said Carrie Kurlander, vice president of public relations and public affairs at Chick-fil-A.
Panera "rarely" reduces calories in reaction to its voluntarily menu labeling, and instead its menu is driven by what chefs and bakers think are the highest-quality ingredients, said Sara Burnett, director of wellness and food policy at the company.
In an emailed statement, a Starbucks representative said the company allows customers to customize beverages and provides nutritional information on its mobile app and website, but it did not address whether it has reduced calories in menu items since it began posting the calorie counts.
Jamba Juice and McDonald's did not respond to CNN's requests for comment.
Creating a chance to eat healthier
However, there are hints from research on local laws that restaurants might cut calories when they have to post them in their menus. One study
found that the number of calories in an average entree at 37 chain restaurants in King County, Washington, dropped from 818 to 777 after a county law went into effect in 2009 requiring menu labeling. (The amount of sodium and saturated fat in entrees, which also has to be posted, went down, too.)
In the United States, six counties, three cities -- New York, Nashville and Philadelphia -- and four states -- California, Maine, Massachusetts and Oregon -- require calorie posting at chain restaurants.
The federal law that will go into effect on December 1, 2016, will require the restaurants and any business that sells ready-to-eat or prepared foods -- including convenience stores, take-out restaurants, big-box stores and movie theaters -- to display calories on their menus. They must also post that information about sodium, fat, carbohydrates and other nutritional information is available upon request.
"Chain restaurants are very formulaic and don't often have individual recipes at the local level. Which is why national menu labeling is such a great opportunity and could have a greater effect than local laws, because it's easier for these corporations to make changes at the national level," said Julia A. Wolfson, a doctoral student in the Department of Health Policy and Management at the Johns Hopkins Bloomberg School of Public Health and a Lerner Fellow in the Johns Hopkins Center for a Livable Future. Wolfson is one of the authors of the current study.
has suggested that just listing calories on a menu doesn't change what customers order. Another study
published Monday found that customers at chain restaurants in New York City ordered about the same number of calories in 2013 and 2014 as they did in 2008, when the city first started to require menu labeling. It also found that the number of customers who noticed the calorie listing on menus diminished over those years.
Still, the federal menu labeling law could help diners consume fewer calories. There is also some indication in the Health Affairs study that even chains that are not posting calories yet could already be making their menus healthier. The researchers found that these restaurants reduced the calories in their new menu items from 519 in 2012 to 419 in 2014.
"It makes it easier if (all) the menu items have fewer calories, then people will automatically order fewer calories," said Block, the assistant professor who led the study.
Surprisingly, new menu items in the chains that voluntarily post rose from 232 in 2012 to 309 in 2014. "It may be a floor that (these restaurants) can only reduce calories so much and they feel they already have it. They also have to compete in the marketplace for people that are looking for tasty items," Block said.