Also, the symbol n (or ω) represents the locant of the methyl end, counted from the carboxyl end of the fatty acid carbon chain. In the expressions n−x or ω− x, the symbol is a minus sign rather than a hyphen (or dash), although it is never read as such. This classification scheme is useful since most chemical changes occur at the carboxyl end of the molecule, while the methyl group and its nearest double bond are unchanged in most chemical or enzymatic reactions. Thus, in omega −3 fatty acids in particular, there is a double bond located at the carbon numbered 3, starting from the methyl end of the fatty acid chain. In general terminology, n (or ω) represents the locant of the methyl end of the molecule, while the number n−x (or ω− x) refers to the locant of its nearest double bond. One way in which an unsaturated fatty acid is named is determined by the location, in its carbon chain, of the double bond which is closest to the methyl end of the molecule. The terms ω−3 ("omega−3") fatty acid and n−3 fatty acid are derived from the nomenclature of organic chemistry. Hence, ALA is a ω−3 fatty acid with ω = 18. The omega (ω) end of the chain is at carbon 18, and the double bond closest to the omega carbon begins at carbon 15 = 18−3. Main article: Fatty acid § Nomenclature Chemical structure of α-linolenic acid (ALA), a fatty acid with a chain of 18 carbons with three double bonds on carbons numbered 9, 12, and 15. Historically, whole food diets contained sufficient amounts of omega−3, but because omega−3 is readily oxidized, the trend toward shelf-stable processed foods has led to a deficiency in omega−3 in manufactured foods. The Canadian Food Inspection Agency has recognized the importance of DHA omega−3 and permits the following claim for DHA: "DHA, an omega−3 fatty acid, supports the normal physical development of the brain, eyes, and nerves primarily in children under two years of age." This updated and modified their health risk advice letter of 2001 (see below). Food and Drug Administration gave "qualified health claim" status to EPA and DHA omega−3 fatty acids, stating, "supportive but not conclusive research shows that consumption of EPA and DHA fatty acids may reduce the risk of coronary heart disease". Subsequently, awareness of the health benefits of essential fatty acids has dramatically increased since the 1980s. ![]() Since then, researchers have shown a growing interest in unsaturated essential fatty acids as they form the framework for the organism's cell membranes. The Burrs coined the phrase "essential fatty acids". If fatty acids were absent from the diet, a life-threatening deficiency syndrome ensued. In 1929, George and Mildred Burr discovered that fatty acids were critical to health. Furthermore, fish oil supplement studies have failed to support claims of preventing heart attacks or strokes or any vascular disease outcomes. There is no high-quality evidence that dietary supplementation with omega−3 fatty acids reduces the risk of cancer or cardiovascular disease. In foods exposed to air, unsaturated fatty acids are vulnerable to oxidation and rancidity. The ability to make the longer-chain omega−3 fatty acids from ALA may be impaired in aging. Namely, ALA (18 carbons and 3 double bonds) is used to make EPA (20 carbons and 5 double bonds), which is then used to make DHA (22 carbons and 6 double bonds). However, they can use ALA, when available, to form EPA and DHA, by creating additional double bonds along its carbon chain ( desaturation) and extending it ( elongation). Mammals are unable to synthesize the essential omega−3 fatty acid ALA and can only obtain it through diet. Common sources of plant oils containing ALA include walnuts, edible seeds, and flaxseeds as well as hempseed oil, while sources of EPA and DHA include fish and fish oils, and algae oil. DHA and EPA accumulate in fish that eat these algae. ![]() Marine algae and phytoplankton are primary sources of omega−3 fatty acids. ALA can be found in plants, while DHA and EPA are found in algae and fish. The three types of omega−3 fatty acids involved in human physiology are α-linolenic acid (ALA), eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). They are widely distributed in nature, being important constituents of animal lipid metabolism, and they play an important role in the human diet and in human physiology. Omega−3 fatty acids, also called Omega−3 oils, ω−3 fatty acids or n−3 fatty acids, are polyunsaturated fatty acids (PUFAs) characterized by the presence of a double bond, three atoms away from the terminal methyl group in their chemical structure.
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