Fatty acids are classified as saturated or unsaturated on the basis of the absence or presence of double bonds. Fatty acids that have no double bonds are “saturated” with hydrogen atoms, hence the name. MUFAs have one double bond; PUFAs have more than one double bond. Oleic acid is the major dietary MUFA. Also important is the cis- versus trans-configuration of the double bonds because it impacts physical and chemical properties. All double bonds in fatty acids are assumed to be in the cis-configuration unless otherwise noted to be trans-. Natural trans fatty acids occur in limited amounts in beef, lamb, and dairy products, which are the predominant dietary sources. Most are produced during chemical hydrogenation of unsaturated fats when some of the cis-isomers are converted to the trans-configuration instead of undergoing complete hydrogenation.