Most people consider fatty acids in the diet in terms of their energy content, and this is because fatty acids possess hydrocarbon chains which makes them a concentrated form of energy. In contrast proteins are known more for their use as structural components of cells and tissues, particularly in skeletal muscle. However, the role for a particular group of fatty acids, those belonging to the omega-3 family, as structural components of cell membranes in nerves and the retina is well established. Omega-3 fatty acids are polyunsaturated fatty acids with their first double bond 3 carbons from the omega (methyl) end of the molecule, and include the essential fatty acid alpha linolenic acid (ALA, C18:3 (n-3)), which is metabolised through a series of elongation and desaturation reactions to produce the two longer chain fatty acids eicosapentaenoic acid (EPA, C20:5 (n-3)) and docosahexaenoic acid (DHA, C22:6 (n-3)). Both EPA and DHA can also be ingested directly in the diet from fatty fish.
Most dietary ALA from sources such as walnuts, green leafy vegetables and flax seeds is preferentially oxidised as a source of fuel, but some of the intake is used to synthesise EPA and DHA. Evidence suggests that the efficiency of converting ALA to EPA in humans is around 5 to 15 % depending on a number of dietary factor including the omega-6 fatty acid intake (excessive linoleic acid (LA, C18:2 (n-6)) imparis conversion) and the degree of insulin resistance in the subject. Incorporation of omega-3 fatty acids into cell membranes can alter cell function because the kinked nature of the molecules makes the cell membranes more fluid and in neuronal tissue this facilitates more efficient generation of action potentials. Further, EPA and DHA can be synthesised into a range of series 3 eicosanoid and docosanoid molecules, respectively. Series 3 eicosanoids and docosanoids have a range of functions but they are particularly well researched for their anti-inflammatory effects and their ability to modulate cell function.
Because of their pivotal role as structural components of cell membranes in nervous tissue, the omega-3 fatty acids have been investigated for their effects on mental function. Some evidence suggests that higher intakes of omega 3 fatty acids are associated with a lower risk of developing depression. However, it is not the absolute levels of omega-3 fatty acids that might be important in this regard but the ratio of omega-3 to omega-6 fatty acids that are the determining factor. For example, in one study, researchers 1investigated the intakes of omega-3 and omega-6 fatty acid using dietary recall in healthy women and tried to find associations with depressive symptoms from medical records. The results showed that higher intakes of omega-3 fatty acids both alone and in relation to omega-6 intake was associated with a reduced risk of elevated depressive symptoms in the women. These results therefore support other studies that show that lower intakes of omega-3 fatty acids may increase the risk of depression.
Dr Robert Barrington’s Nutritional Recommendation: A shift from a traditional eating pattern containing whole unrefined plant foods to one of refined carbohydrates and oils has paid a heavy toll on the health of Westerners. The refined carbohydrates increase insulin resistance and this inhibits flux of omega-3 fatty acids through the essential fatty acid pathway. In addition, the refined oils that are common in the Western diet contain too many omega-6 fatty acids which further limits production of the longer chain omega-3 fatty acids required for cell function. The ratio of omega-6 fatty acids to omega -3 fatty acids in the western diet might be as high as 10 to 20 to 1, but research suggests that traditionally this ratio was 3 to 1. Increasing the intake of omega-3 fatty acids and limiting the intake of omega-6 fatty acids to return this ratio to the traditional values is an important step in producing a healthy human being.
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