Omega-3 and omega-6 fatty acids are two group of long chain polyunsaturated fatty acids that are stored in cell membranes and subsequently converted into short lived hormones called eicosanoids. These short lived hormones that include subgroups such as thromboxanes, prostacyclins, prostaglandins and leukotrienes regulate a number of cell functions including the inflammatory reaction. A balance between intakes of omega-6 and omega-3 fatty acid is required to maintain health through a balanced production of eicosanoids. However, the Western diet contains too much omega-6 fat and too little omega-3 fat and this imbalance causes pro-inflammatory eicosanoids to predominate, and this may be a major cause of Western lifestyle diseases. The omega-6 to omega-3 fatty acid ratio in the Western diet maybe as high as 10 or 20 to 1. Increasing omega-3 fatty acid intake (and lowering omega-6 fatty acid intake) is therefore recommended in order to return the ratio of omega-6 to omega-3 fatty acids to around 3 to 1.
To be effective, dietary omega-3 fatty acids must be converted to eicosapentaenoic acid (EPA, C20:4 (n-3)). Dietary plant sources of omega-3 fatty acids are available and include hemp seed, green leafy vegetables, walnuts and flax seeds. These supply the omega-3 fatty acid alpha linolenic acid (ALA, C18:3 (n-3)) which can be converted to EPA in humans. However, conversion of ALA to EPA in humans is inefficient due to the rate limiting enzyme delta 6-desaturase, and plant sources of omega-3 fatty acid might not be as efficient at raising cell membrane levels of omega-3 derived eicosanoids compared to fish oils. This relates to the fact that the fish oils contain preformed EPA. In addition, fish also contains docosahexaenoic acid (DHA, C22:6 (n-3)) that enter the eicosanoid synthesis pathways past the rate limiting delta 6-desaturase bottleneck. However, as vegetarians cannot consume fish, they must rely on plant sources of omega-3 fatty acids to a greater extent that non-vegetarians.
However, some plants contain high activity of delta 6-desaturase and are able to convert ALA to stearidonic acid (SDA, C18:4 (n-3)) and thus provide a source of omega-3 fatty acids that is past the rate limiting step in the metabolic pathway. For example, seeds from the echium species of plant Echium plantagineum of the family Boraginaceae contain 10 to 15 % SDA and 30 to 40 % ALA (as well as 10 % gamma linolenic acid (GLA, C18:3 (n-6))). This makes echium seed oils a very good source of omega 3 fatty acids. The ability of echium seed oil to increase cell membranes EPA concentrations in humans has been investigated. For example in one study1, researchers fed subjects with the metabolic syndrome 17 grams per day of echium oil. Health normal weight subjects were administered 17 grams per day of either echium oil or fish oils. During the 10 week study the subjects were asked to limit fish intake and other sources of omega-3 fatty acids in order to allow accurate measurement of the effects of the treatments.
After 8 weeks of supplementation, fish oil supplements increased long chain fatty acids in blood, including EPA, about twice as much as echium oil. Supplementation with echium oil increased mononuclear cell concentrations of EPA significantly, but DHA levels decreased. As body mass index increased, the effects of the echium oil were less pronounced, suggesting that a greater volume of adiposity may inhibit the accumulation of omega-3 fatty acids in blood. This may relate to insulin resistance in obesity, which is a known inhibitor of ALA metabolism, or may be due to the fatty acids being sequestered in body fat. Echium oil supplementation significantly reduced serum cholesterol, low density lipoprotein (LDL) cholesterol, oxidised LDL and triglycerides. Echium oil may therefore be an effective source of omega-3 fatty acids. However, fish oils are still the supplement of choice because they contain preformed EPA which is more efficient at raising cell membrane levels of EPA.
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