What does "trans" mean?

Fatty acids are the main constituents of fats and oils. Their molecules can have two different chemical structures: The most common is the "cis" form, but they can also exist in the "trans" form. This trans form has two origins: it is derived either from the biohydrogenation process (hydrogenation occurring spontaneously in the stomach of ruminants) or from the partial hydrogenation used to obtain a firm texture.

Note that the term "trans" has nothing to do with the term transgenic.

Some trans fatty acids when consumed to excess can increase the risk of cardiovascular disease. It should, however, be stated that almost all margarines and fat- or oil-based spreads contain less than 1% of trans fatty acids, which could be considered negligible.

Source: IFN