Starting Friday, restaurants in California can no longer use any oils, margarine or shortening that contain trans fats.
Governor Arnold Schwarzenegger signed the measure into law in 2008, but the effective date was 2010 to give restaurants time to adjust.
Heather Buonomo is a health inspector for San Diego County. She says many restaurants have already made the transition.
"Now there is one exception," Buonomo says. "Restaurants that fry yeast, dough or cake batter such as in doughnuts, they're going to have till Jan 2011, and that's going to give them a little more time to find a suitable alternative."
Transfats contribute to heart disease by increasing cholesterol levels.
The new law also applies to private schools, grocery stores, bakeries and other retail food facilities.
Public schools in California are already banned from using transfats in meals.