The second phase of California's ban on artificial trans fats was set to take effect January 1, meaning restaurants must stop using oil with trans fat for cake batter, donuts and other items.

California became the first U.S. state to ban artificial trans fat in restaurants when it enacted the law in July 2008, and the first phase of the law took effect January 1 last year and included a ban on trans fats in oil, shortening and margarine used in spreads or for frying.

Under the second phase of the ban no food containing 0.5 grams or more of artificial trans fat per serving may be stored, distributed, served by or used in the preparation of any food within a food facility.

The prohibition also applies to the deep frying of yeast dough or cake batter, two items which previously were exempt from the ban.

Restaurants in violation of the ban are subject to a fine of not less than $25 or more than $1,000.