Keyword : cis, trans 

The term cis and trans describe the configuration of the hydrogen atoms attached to the carbon atoms in double bonds of unsaturated oils. In the cis-configuration, these hydrogen atoms are located on the same side of the plane containing the carbon to carbon double bonds. Most naturally occurring fatty acids are cis isomers, but small quantities of trans fatty acids do occur naturally in ruminant fats and dairy products. However, partial hydrogenation will cause the formation of trans-fatty acids.