The national calorie disclosure rule is part of the Affordable Care Act of 2010, also known as Obamacare and aims to help consumers battle the bulge since Americans eat and drink about one-third of their calories away from home.

The regulation requires calories to be listed on menus and menu boards at restaurants and other food retail establishments with 20 or more locations. In most cases, they also apply to vending machine operators with 20 or more units.

The postponement from the previous Dec. 1 deadline was contained in final guidance from the Food and Drug Administration released on May 5.

The rule's start date has been so delayed that early critics, such as McDonald's Corp, have been displaying such information for years in compliance with rules set by California, New York City and other jurisdictions.

"I'm hopeful that the date will stick," said Margo Wootan, director of nutrition policy at the Center for Science in the Public Interest, a long-time proponent.

Lobbyists for Domino's Pizza Inc, convenience stores and supermarkets helped push back the previous federal deadline, and the U.S. House of Representatives in February passed legislation aimed at the weakening rule.

Tackling the American obesity epidemic has been a signature issue for the White House and first lady Michelle Obama.

The White House publicly opposed the House bill saying it "would undercut the objective of providing clear, consistent calorie information to consumers." But, it stopped short of issuing a formal veto threat.

Wootan and other experts said that the Senate version of the opposition bill is expected to stall.