California has become the first US state to force fast-food restaurant chains to list calories on their menus.
While New York officials introduced a similar law in April, California is the first state to impose the calorie-count in a bid to tackle obesity.
From 1 July 2009 fast-food chains with more than 20 outlets will be required to offer diners a list detailing the calorie counts and nutritional information of their menus.
From 1 January 2011 they will need to list this information on their menus and menu boards.
California governor Arnold Schwarzenegger said: "This legislation will help Californians make more informed, healthier choices by making calorie information easily accessible at thousands of restaurants throughout our state."
The California Restaurant Association, which represents 22,000 operators said it welcomed the decision.
The group's president and chief executive Jot Condie told news service Reuters it favoured a state law over a patchwork of local measures.
"I think New York was probably the closest thing to a laboratory in this regard. It hasn't impacted the bottom line to restaurants," he said.
In July, California became the first US state to ban restaurants from preparing food with trans fats, which clog arteries and raise the risk of heart disease.
While the UK's Food Standards Agency is keen to improve the information available to consumers eating out but mandatory regulations for menu labelling are not on the cards at present.
By Kerstin Kühn
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