Gov. Arnold Schwarzenegger signed legislation that will ban restaurants and other retail food establishments from using oil, margarine and shortening containing trans fats.
In a statement, Schwarzenegger noted that consuming trans fat is linked to coronary heart disease.
"Today we are taking a strong step toward creating a healthier future for California," he said.
Violations could result in fines of $25 to $1,000. Food items sold in their manufacturers' sealed packaging would be exempt.
New York City, Philadelphia, Seattle, Baltimore and Montgomery County, Md., have ordinances banning trans fats, but California is the first state to adopt such a law covering restaurants, said Amy Winterfeld, a health policy analyst for the National Conference of State Legislatures.
California and Oregon already had laws banning trans fats in meals served at schools, she added.
The legislation signed by Schwarzenegger will take effect Jan. 1, 2010, for oil, shortening and margarine used in spreads or for frying. Restaurants could continue using trans fats to deep-fry yeast dough and in cake batter until Jan. 1, 2011.
Trans fats occur naturally in small amounts in meat and dairy products. Most trans fats are created when vegetable oil is treated with hydrogen to create baked and fried goods with a longer shelf life.
Stephen Joseph, a Tiburon attorney who was a consultant to New York City in developing its ban, said trans fat is a larger health risk than saturated fat because it reduces so-called good cholesterol.