NEW YORK - McDonald's restaurants in the U.S. 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 notes 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."

The chain also plans to announce that its restaurants in Latin America, which are owned by a franchisee, will start providing calorie information on menus this spring.

McDonald's, based in Oak Brook, Ill., already posts calorie information in Australia, South Korea and the United Kingdom.

The decision to post calorie information in the U.S. 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.

Corporate Accountability International, which has urged McDonald's to stop marketing its food to children, notes that the chain has fought efforts to institute menu labeling in local jurisdictions in the past and said its latest move was "certainly not voluntary."

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.

Joe Finn, a sales manager from Oconomowoc, Wis., said he was surprised at the calorie information posted at a hamburger restaurant when he flew out to California earlier this year for the Rose Bowl.

"All the calories were up there, and I thought, well, I'm not going to order that," said Finn, 51, who's trying to watch what he eats. He ended up picking the most basic burger, without cheese. Back at home, he tries to stick to options where he knows the calorie information, such as Subway sandwiches.

"Otherwise you could be ordering a gut bomb," he said.

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

The Wendy's Co. did not immediately respond to requests for comment. Representatives for Burger King Worldwide Inc. and Yum Brands Inc, which owns Taco Bell and KFC, said they're waiting for further guidance from regulators before updating their menus.

McDonald's is also testing healthier options for next year, such as an Egg McMuffin made with egg whites and a whole grain muffin. The 260-calorie sandwich has Canadian bacon and white cheddar cheese. It will be called the Egg White Delight.

The chain is also testing versions of the McWrap, a bigger version of its chicken Snack Wrap that is already sold in Europe. The wraps have sliced cucumbers and range from 350 to 580 calories.

The moves reflect the pressures McDonald's and other fast-food chains are facing amid growing concerns about obesity.

A meal consisting of a Big Mac and medium fries, for example, has 920 calories. Add a 16-ounce Coca-Cola, and the count rises to 1,140 calories.

As for the company's move earlier this year to automatically include apple slices in its Happy Meals, Sara Deon of Corporate Accountability said it amounted to a "PR scheme designed to drive traffic to stores to sell burgers and fries."

McDonald's also faces competition from chains such as Subway, which positions itself as a healthy alternative to traditional hamburger chains.

McDonald's, which has 14,000 locations in the U.S., doesn't plan to advertise the posting of the calorie information. Fields said it's something the chain is doing as a "customer convenience."