Polyunsaturated fatty acids (PUFA) from plants have important health implications because two of these fatty acids, α-linolenic acid (ALA, C18:3 (n-3)) and linoleic acid (LA, C18:2 (n-6)) are essential to health. Unsaturated fatty acids have double bonds that gives the molecules pronounced kinks, and this lowers their boiling point and makes them liquids at room temperature. Incorporation of unsaturated fatty acids into cell membranes therefore increases fluidity. Metabolism of ALA and LA to the longer more unsaturated fatty acid eicosapentanoic acid (EPA, C20:5 (n-3)) and arachidonic acid (AA, C20:4 (n-6)), respectively, provides the substrates for the production of autocrine hormones called eicosanoids. These hormones regulate cell function including controlling inflammation, clotting and blood pressure and are therefore vital to health. Fish oils provide a source of EPA directly, although LA may still be required for the synthesis of dihomo-γ-linolenic acid (DGLA, C20:3 (n-6)).
Unsaturated fats are prone to oxidation particularly following application of heat and light. Because of this manufacturers have been slowly removing these fats from the food supply to increase the shelf life of their products. This is particularly true for ALA which has three double bonds and can be considered unstable at room temperature. Removal of ALA from the diet of Westerners has resulted widespread deficiencies of omega 3 fatty acids, and also created an imbalance in the delicate intake ratio required between ALA and LA, which has shifted towards too much LA and too little ALA. The result of the current widespread imbalance in essential fatty acids is a rise in the Western lifestyle disease such as cancer, cardiovascular disease, obesity and type 2 diabetes. This problem is exacerbated by the increased dietary consumption of chemically altered and adulterated fatty acids that are a by-products of food manufacture and processing.
Hydrogenation is used in the food manufacturing process because it elongates shelf life and produces spreadable products such as margarine and butter substitutes. Hydrogenation is a process by which hydrogen gas is passed over unsaturated oils at high temperatures and pressures. This results in the production of a cheap saturated fatty acid if the process is allowed to go to completion. Saturated fatty acids do not have negative effects in the body and so hydrogenation results in the production of neutral fats. Hydrogenation therefore is not in itself detrimental to health, and is in reality a chemical process that mimics the enzymatic production of saturated fatty acids in animals and plants. However, the deleterious effects of hydrogenation may come from the presence of the catalysts used in the process that can include nickel and aluminium. Residues of these metals, if let in the oil, may have deleterious health effects.
However, hydrogenation during the manufacture of margarine and spreads is not usually allowed to reach completion. This results in partial hydrogenation of unsaturated fatty acids and causes the production of transitional products that are halfway between the natural unsaturated oil and the saturated end products of full hydrogenation. These products can include oxidised fatty acids with modified double bond positions and trans fatty acids. Both of these products are known to increase oxidative stress in humans and the latter is now implicated in the development of cardiovascular disease and cancer. Trans fatty acids are particularly problematic because they are often not recognised by human metabolising enzymes and therefore interfere with metabolic pathways and essential fatty acid metabolism. Partially hydrogenated oils contain trans fatty acids mainly of 18 carbons in length and have double bonds in the Δ8, Δ9, Δ10, Δ11 and Δ12 positions, with elaidic acid (t-C18:1 (Δ9)) being particularly problematic.
Deodorised supermarket oils are PUFA such as corn, rape and sunflower that have been processed to remove their plant material including antioxidants. This process involves the application of heat and pressure and this can cause chemical alteration to the oil that can lead to the production of oxidised fatty acids that, when consumed, cause inflammation and disease. Plant antioxidants in natural PUFA protect the oil in nuts and seeds and prevent rancidity. Removing these antioxidants increases the susceptibility of the oils to oxidation, which further causes deleterious effects in the chemical composition of the oils. By law extra virgin olive oil can only be labelled as such if the product has not undergone this process, resulting in the production of a cold pressed healthy oil. Unless oils made from PUFA are unprocessed and are present in opaque bottle in refrigerators, they will be highly oxidised and therefore consumption will lead to inflammation and disease.
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