What are trans fats?

Most trans fats are formed through an industrial process that adds hydrogen to vegetable oil, which causes the oil to become solid at room temperature.

This partially hydrogenated oil is inexpensive and less likely to spoil, so foods made with it have a longer shelf life. Some restaurants use partially hydrogenated vegetable oil in their deep fryers, because it doesn't have to be changed as often as do other oils.

Some meat and dairy products have a small amount of naturally occurring trans fats. However, it's not clear how these trans fats affect health.