You probably heard a million times about trans fat. Pretty much everybody agrees that trans fat are bad for you health and that you should avoid them.
To understand about trans fat we have to talk in chemistry terms. But do not worry is not that difficult at all. Fats are made of a glycerol (an alcohol, just as the ethanol you drink in your beer or wine) molecule bonded to three fatty acid molecules. Fatty acids are long chains of carbon atoms with hydrogen attached to them.
Fatty acids can be divided in 2 groups according to wheter tehy have double bonds or not. Those with double bonds are called unsaturated. Those with NO double bonds are called saturated. Saturated fats are usually solid at room temperature (lard, butter, etc) while unsaturated are usually liquid (vegetable oils).
When a long molecule (such as a fatty acid) has a double bond it can adopt two types of configurations: a cis-configuration or a trans configuration. In the cis form both hidrogens on the double bond are on the same side of the molecule: on the trans each hydrogen is on the opposite side of the molecule (see figure bellow).
Trans fat may occur naturally or artificially (created by technology). If you take a vegetable oil (that has a lot of unsaturated fatty acids) and break the double bonds it has, and add hydrogen (by a process called hydrogenation) you get a vegetable oil with saturated fatty acids. Those naturally occurring cis-fatty acid are hydrogenated (saturated) and become of the trans type.
Trans fat, Why are they bad?
They are associated with heart disease. Trans fat have shown to raise small and dense LDL (bad) cholesterol levels, as well as lowered HDL (good) levels. According to research studies, they massively increase chances of developing heart disease.
Now, it is important to understand that there are naturally occurring trans fats in meat and dairy products. These naturally occurring trans fat are actually good for health. One of them is called Conjugated Linoleic Acid (CLA). The problem is with the overfeeding of artificially created trans fats in processed food.
If you follow a traditional diet (an there are many types of them) you do not need to worry about trans fat since the amount you will consume in meat and dairy is not high enough to cause problems and actually you may benefit from them. The problem arise when we eat food enriched with artificially created fats (vegetable oils hydrogenated). These contain abnormally high concentrations of trans fat that are foreign to humans. Stay away of margarines or soft butters and spreads made by hydrogenation. Eat whole foods and you will be on the right path to a