Trans fatty acids, or trans fats, are made when manufacturers add hydrogen to liquid vegetable oil—a process called hydrogenation—creating solid fats like shortening and hard margarine. Hydrogenation increases the shelf life and flavor stability of foods containing these fats. Diets high in trans fat raise the LDL (low density lipoprotein) or “bad” cholesterol, increasing the risk for coronary heart disease.

Cakes, crackers, cookies, snack foods, and other foods made with or fried in partially hydrogenated oils are the largest source (40 percent) of trans fats in the American diet. Animal products and margarine are also major sources of trans fats. Since January 2006, the U.S. government has directed that the amount of trans fat in a product must be included in the Nutrition Facts panel on food labels. In 2008, California became the first state to enact legislation to gradually phase trans fat out of foods served in food facilities and in baked goods. Similarly, New York City is phasing in a ban on trans fat in all city restaurants. Other states have proposed legislation to ban the use of trans fats in restaurants or schools or baked goods.