Trans fat behaves like saturated fat by raising low-density lipoprotein (LDL or "bad") cholesterol that increases your risk of coronary heart disease (CHD). Trans fat can be found in some of the same foods as saturated fat, such as vegetable shortenings, some margarines, crackers, candies, cookies, snack foods, fried foods, baked goods, and other processed foods made with partially hydrogenated vegetable oils.

Trans fat is made when hydrogen is added to vegetable oil -- a process called hydrogenation. Hydrogenation increases the shelf life and flavor stability of foods containing these fats. Usually the hydrogen atoms at a double bond are positioned on the same side of the carbon chain. However, partial hydrogenation reconfigures some double bonds and the hydrogen atoms end up on different sides of the chain. This type of configuration is called "trans" (means "across" in Latin). The structure of a trans unsaturated chemical bond looks like the diagram below.

As stated in FDA's labeling regulations, if a fat or oil ingredient is completely hydrogenated, the name in the ingredient list will include the term "hydrogenated." Or, if partially hydrogenated, the name in the ingredient list will include the term "partially hydrogenated." As stated above, oil that is partially hydrogenated is a source of trans fat.

There again...
since im researching into such info... I went to check the difference between saturated and unsaturated fats. Although these were all taught in biology lessons, but i guess i have returned most of them to the teachers. hehe. =P

Saturated fats contribute to higher levels of LDL (bad) cholesterol, says the U.S. National Library of Medicine, and should be avoided in large amounts. Foods that are typically high in saturated fat include animal products like butter, cheese, whole milk, ice cream, and fat-laden meats. Some vegetable oils -- such as those from coconut, palm, and palm kernel -- are also high in saturated fats.

Unsaturated fats can actually lower levels of LDL cholesterol, so they are a good alternative to saturated fats. But even unsaturated fats are still high in calories, so excessive amounts in the diet should be avoided. Foods that are a good source of unsaturated fats include olives and olive oil, peanuts, and avocados.

-- Diana Kohnle