As calories count the most in the struggle against obesity, a new rule demanding New York chain restaurants to put calorie information right on their menus took effect on Friday, thus marking a first for a U.S. city.

As part of a campaign against obesity, the regulation requires restaurants that have 15 or more outlets across the country to put calorie counts next to their prices and it concerns more than 2,000 restaurants or 10 percent of the total in the city. Among them are such restaurants as McDonald's, Burger King, Applebee's — operated by DineEquity Inc — Dunkin Donuts, Starbucks and Subway.

Starting on Saturday, NYC health inspectors can issue fines ranging from $200 to $2,000 to fast food and casual-dining chains if calorie counts are not shown on their menus in the same font and format as the name or price of food items.

New York residents seemed undisturbed by the rule, and some said they would not be discouraged from getting a 540-calorie Big Mac at McDonald's or a 440-calorie Iced Lemon Loaf at Starbucks.

Although analysts anticipate the decision not to have much impact on consumer habits, officials say it could prevent at least 150,000 New York inhabitants from becoming obese and stop at least 30,000 from developing diabetes over the next five years.

A city study conducted last year revealed that 30 percent of New Yorkers were swallowing more than 1,000 calories at lunchtime.

The health code stipulation, which interferes with businesses of at least 15 establishments nationwide, was postponed when the New York State Restaurant Association went to court. In April, a higher court rejected to delay the rule further after the restaurant association appealed because of a federal judge upholding the rule.