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 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., 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."

Danya Proud, a spokeswoman for McDonald's, says the company didn't suport local efforts to reuqire menu labeling because it wanted a national standard.

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.