Polyunsaturated fats have multiple double bonds in their carbon chains and this makes them liquid oils at room temperature because they have low melting points compared to solid saturated fats. When polyunsaturated fats are hydrogenated during processing, the double bonds are broken and saturation of the carbon chain proceeds. If this process is left to completion, a hydrogenated fat is formed. This fat is identical to a saturated fat of the same length chemically. Hydrogenation of the polyunsaturated fatty acid alpha linolenic acid (ALA, C18:3 (n-3)) would for example stearic acid (SA, C18:0), a saturated fat. This process is advantageous to food manufacturers because it allow the creation of solid fats from liquid oils, and also allows the label to make health claims that the produce contains polyunsaturated fats. Margarine for example is solid because the chemistry of the oil have been changed through hydrogenation, so the original liquid polyunsaturated oil (usually sunflower) becomes solid at room temperature.
However, during the hydrogenation process not all fats are saturated, some become partially hydrogenated. Partial hydrogenation results in the formation of trans fats. Natural unsaturated fats tend to have a cis configuration in their double bonds. This means that both hydrogens are on the same side of the molecule, and the charge causes them to repel each other, bending the carbon chain. Unsaturated oils therefore have a specific shape, which is highly kinked, and this shape relates to the number and location of the double bonds. Trans fats do not retain the cis configuration, but instead have a trans configuration double bonds, whereby the hydrogens are on opposite sides of the carbon chain. The change to the charge location based on relocation of the hydrogens changes the shape of the molecule creating a class of fats that are not represented in nature. These fats are not recognised by human metabolism, and evidence suggest they are similar enough in structure to interfere with the metabolism of other fats.
Trans fats may interfere with naturally occurring fats such as the essential fatty acids linoleic acid (LA, C18:2 (n-6)) and alpha linolenic acid (ALA, C18:3 (n-3)). The essential fats are synthesised in humans to eicosanoids, short lived hormones that control cell function. Trans fat are therefore metabolic poisons because they interfere with the synthesis eicosanoids, and this may have serious consequences on cellular metabolism. Trans fats have been shown to increase the risk of cardiovascular disease significantly, perhaps through their effects on essential fatty acid metabolism. Recently trans fats have also been shown to increases the risk of stroke. In one study1, trans fat intake was shown to be associated with an increased risk of stroke in men, but not women. For every 2 grams of trans fat in the diet, there was a 14 % increase in the risk of stroke. The sex discrepancy may result from the higher trans fat intake in men compared to women, or may indicate differential metabolism of trans fats between men and women,
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