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Though a negligible amount of trans fats are found naturally (in mostly animal foods and early clinical research shows an important role of these naturally occurring trans fatty acids in the immune system), the vast majority are formed during the manufacture of processed foods (see below for details). In unprocessed foods, most unsaturated bonds in fatty acids are in the cis configuration.
Trans fat from partially hydrogenated vegetable oils has displaced natural solid fats and liquid oils in many areas.
Partial hydrogenation increases the shelf life and flavor stability of foods containing these fats. Partial hydrogenation also raises the melting point, producing a semi-solid material, which is much more desirable for use in baking than liquid oils. Partially hydrogenated vegetable oils are much less expensive than the fats originally favored by bakers, such as butter or lard. Because they are not derived from animals, there are fewer objections to their use.
Snack foods, fried foods, baked goods, salad dressings, and other processed foods are therefore likely to contain it, as are vegetable shortenings and margarines. Laboratory analysis alone can determine the amount.Though some newer variants differ, most margarines have much more trans fat than butter. In the 1950's advocates said that the trans fats of margarine were healthier than the saturated fats of butter. Some say the theory that saturated fats are unhealthy is wrong anyway. See the saturated fats page for details.
Trans fatty acids are made when manufacturers add hydrogen to vegetable oil, in the presence of small amounts of metals such as nickel or cobaltiron cobalt nickel Co Rh Full table General Name, Symbol, Numbercobalt, Co, 27 Chemical series transition metals Group, Period, Block 9, 4, d Density, Hardness 8900 kg/m3, 5. 0 Appearance metallic with grey tinge Atomic properties Atomic weight 58. 933200 -- in a process described as partial hydrogenationHydrogenation is a chemical reaction in which unsaturated bonds between carbon atoms are reduced by attachment of a hydrogen atom to each carbon. The process thus results in the saturation of the carbon atoms, meaning that each carbon atom has 4 other ato. If the hydrogenation process were allowed to go to completion, there would be no trans fatty acids left, but the resulting material would be too solid for practical use. A claimed exception to this is Kraft Food's new trans fat free Crisco which contains the wax-like fully hydrogenated cottonseed oil blended with liquid vegetable oils to yield a shortening much like the previous Crisco which was made from partially hydrogenated vegetable oil. However any hydrogenated or partially hydrogenated oil will contain trace amounts of the metals used in the process of hydrogenation. Usually the hydrogen atoms at a double bond in a natural fatty acid are positioned on the same side of the carbon chain. However, partial hydrogenation reconfigures most of the double bonds that do not become chemically saturated, so that the hydrogen atoms end up on different sides of the chain. This type of configuration is called trans (which means "across" in Latin). The structure of a trans unsaturated chemical bond is shown in the diagram.