An unsaturated fatty acid in which one or more of the double bonds are in the trans configuration. In most naturally occurring unsaturated fatty acids the double bonds are in the cis configuration, in which the hydrocarbon chain is effectively ‘kinked’ at each double bond. Hydrogenation of natural oils to ‘harden’ them is performed in food manufacturing to extend the shelf life of products such as cakes, biscuits, and pastries. A consequence of this is the conversion of cis double bonds to the trans configuration, in which the hydrocarbon chain is not kinked. Studies have shown that trans fatty acids are harmful to health, by lowering levels of ‘good’ cholesterol (in high-density lipoproteins, or HDLs), and health authorities recommend minimizing their intake in the diet.