An overview from the American Heart Association
Trans fat (also called trans fatty acids) is formed when liquid vegetable oils go through a chemical process called hydrogenation, in which hydrogen is added to make the oils more solid. Hydrogenated vegetable fats are used by food processors because they allow longer shelf-life and give food desirable taste, shape, and texture. Evidence suggests that consumption of trans fat raises LDL (“bad”) cholesterol levels and lowers HDL (“good”) cholesterol levels, causing the arteries to become clogged and increasing the risk of developing heart disease and stroke. To read the full story about transfats and other fats, click here.