File Photo: A competitor prepares to go in front of judges for reality television programme "Dance Your Ass Off," during which overweight or obese contestants hope to lose weight by dancing, in New York Dec. 18, 2009. (Xinhua/REUTERS)

WASHINGTON, May 7 (Xinhua) -- A U.S. regulation that went into effect Monday directs chain restaurants to label calories on their menus, in an effort to encourage people to consume in moderation.

The rule, rolled out in 2014, applies to restaurants chains with 20 or more establishments that offer similar food items.

The targeted chains must disclose the number of calories contained in standard items on menus and menu boards.

Businesses must also provide, upon request, written nutrition information for standard menu items, covering fat, sugar, sodium and protein, according to the Food and Drug Administration (FDA).

FDA Commissioner Scott Gottlieb said the new regulation is based on research which shows that when customers are presented with calorie information, they tend to choose food items that contain less energy.

"Studies suggest that access to clear and consistent information about calories in restaurant items can help reduce calorie intake, which over time could make a difference in obesity rates," he said.

Obesity has become a major health issue in the United States, leading to higher chances of heart disease. Studies show the U.S. obesity rate, which continues to grow, is the highest in the world.