McDonald's restaurants in the United States will soon get a new menu addition: the number of calories in the chain's burgers and fries.

The world's biggest hamburger chain said Wednesday that it will post calorie information on restaurant and drive-thru menus nationwide starting Monday. The move comes ahead of a regulation that could require major chains to post the information as early as next year.

"We want to voluntarily do this," said Jan Fields, president of McDonald's USA. "We believe it will help educate customers."

In cities such as New York and Philadelphia where posting calorie information is already required, however, Fields noted that the information has not changed what customers choose to order.

"When it's all said and done, the menu mix doesn't change," she said. "But I do think people feel better knowing this information."

A meal consisting of a Big Mac and medium fries, for example, has 930 calories. Add a medium Coca-Cola, and the count rises to 1,140 calories.

The decision to post calorie information follows the Supreme Court's decision this summer to uphold President Barack Obama's health care overhaul, which includes a regulation that would require restaurant chains with more than 20 locations to post calorie information. The timetable for carrying out that requirement is being worked out.

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The posting of calorie information isn't a magic bullet in fighting obesity but could have a big effect over time, says Margo Wootan, director of nutrition at the Center for Science in the Public Interest, which advocates on nutrition and food safety issues.

"Obesity isn't the kind of thing where one day you wake up and you're fat. We gradually and slowly gain weight over time," she said. So even if only some people are swayed to make slightly better choices, Wootan thinks there's a big benefit to providing calorie information.

Another upside is that companies tend to work harder to provide healthier options when they're forced to display calorie information.

"It can be embarrassing, or shocking, so they end up changing the way the product is made," Wootan said.

The move by McDonald's could spur other restaurant chains to move ahead of the federal regulation.

McDonald's Corp. will post calorie counts on its menus nationwide starting next week. A sampling:

Big Mac: 550

Double Cheeseburger: 440

Filet-O-Fish: 380

Angus Deluxe: 750

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Chicken McNuggets (6-piece): 280

Medium fries: 380

Medium Coke: 210

Medium Iced Latte: 100

Baked Apple Pie: 250

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Strawberry Sundae: 280