Trans fats, also called trans fatty acids, are a type of unsaturated fat.
Trans fats are found naturally in meat and milk of ruminants but only in small amount representing around 2 % to 5 % of total fat.
That vast majority of trans fats are artificial and found in process foods. They are an unintentional by-product of the partial hydrogenation of liquid oils.
The hydrogenation process is used to transform liquid fats into more solid fats and to extend their shelf-life by preventing rancidification. In order to control fat hardness and other properties, the hydrogenation process can be interrupted before the end. This is called partial hydrogenation and is responsible for the production of trans fats.
According to the FNB (Food and Nutrition Board of the Institute of Medicine), trans fats has no required role for the human body. Also, even low intake of trans fats can increase LDL and total cholesterol. Therefore, the intakes of trans fats should be minimized.