Trans fats occur naturally in beef, butter, milk and lamb fats and in commercially prepared, partially hydrogenated margarines and solid cooking fats. The main sources of trans fats in the American diet today are margarine, shortening, commercial frying fats and high-fat baked goods. Partially hydrogenated vegetable oils were developed in part to help displace highly saturated animal and vegetable fats used in frying, baking and spreads. However, trans fats, like saturated fats, may raise blood LDL cholesterol levels (the so-called "bad" cholesterol) - but not as much as the saturates do. At high consumption, levels may also reduce the HDL or "good" cholesterol levels.