Trans fats are unsaturated fatty acids formed when vegetable oils are processed and made more solid or into a more stable liquid. This processing is called hydrogenation. Trans fats also occur naturally in low amounts in some foods.
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, raise blood LDL cholesterol levels (the so-called "bad" cholesterol). High consumption of trans fats may also reduce the HDL or "good" cholesterol levels.
In January 2006, FDA revised food labeling regulations to require that the amount of trans fat in a product be declared on the Nutrition Facts panel.
Reprinted from the International Food Information Council Foundation, (2009)