Nov 04, 2015 12:40 AM EST By J Dionne, UniversityHerald Reporter

Restaurants that voluntarily list calorie counts on their menus sell items that average nearly 140 fewer calories those that do not post the information, Pioneer News reported.

The findings, conducted by a Johns Hopkins Bloomberg School of Public Health-led research group, come as large U.S.-based chain restaurants will be required to post calories on their menus beginning in December 2016. This means American chain restaurants with more than 20 outlets and many other establishments that serve food, including ice cream shops and movie theaters,

Calorie labeling, required as part of the Affordable Care Act, was put in place with the goal of steering people towards lower calorie choices, which could, in turn, help Americans eat more healthfully.

"The menu items in restaurants with voluntary labeling have fewer average calories than restaurants without labeling," study co-author Julia A. Wolfson said in a statement. "If other chain restaurants follow this same trend once mandatory menu labeling goes into effect, it could significantly improve the restaurant environment for consumers. This could get consumers to eat healthier without having to change their behavior, something that is a very difficult thing to do and sustain."

For the study, researchers analyzed data from 2012 to 2014 in MenuStat, a data set of menu items at 66 of the 100 largest U.S. chain restaurants, based on sales, Daily RX News reported.

They found that the chains with voluntary labeling averaged nearly 140 fewer calories per item than those that do not post the calorie counts on menus, with much of that difference attributed to lower-calorie food rather than beverage items. In 2012, the average item at the restaurants posting their calories on their menus contained 260 calories, while the average was 399 calories at those that didn't post calorie counts. In 2014, the average was 263 at those with voluntary labeling and 402 at those without.

The researchers also found similar results when they compared restaurants with voluntary labeling to competitors with similar menu offerings that did not have menu labeling; for example, Chick-fil-A to other chicken restaurants, or McDonald's to other burger restaurants.

While the requirements won't go into effect for another year, five of the 66 largest U.S. restaurant chains have already introduced voluntary calorie counts on menus in all their outlets: Panera and Jamba Juice since 2010, McDonald's since 2012 and Chick-fil-A and Starbucks since 2013.

Researchers say it isn't clear whether the chains with calorie counts on their menus were already serving lower-calorie foods before they decided to go public with their calorie counts, whether calorie counts were lowered in anticipation of the move or whether these chains just happened to have lower calorie counts all along.

The findings are detailed in the journal Health Affairs.

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