Buried deep in the health care legislation that President Obama signed on Tuesday is a new requirement that will affect any American who walks into a McDonald’s, Starbucks or Burger King. Every big restaurant chain in the nation will now be required to put calorie information on their menus and drive-through signs.

In other words, as soon as 2011 it will be impossible to chomp down on a Big Mac without knowing that it contains over 500 calories, more than a quarter of the Agriculture Department’s 2,000-calorie daily guideline.

The legislation also requires labels on food items in vending machines, meaning that anybody tempted by a king-size Snickers bar will know up front that it packs 440 calories.

The measure is intended to create a national policy modeled on a requirement that has already taken effect in New York City and was to go into effect in 2011 in places like California and Oregon. The new federal law requires restaurant chains with 20 or more outlets to disclose calorie counts on their food items and supply information on how many calories a healthy person should eat in a day.