Omega-3 fatty acid

Omega‑3 fatty acids—also referred to as omega‑3 oils, ω‑3 fatty acids, or n‑3 fatty acids—are a type of polyunsaturated fat. Their defining chemical feature is a double bond located three carbon atoms from the terminal methyl group (the end of the molecule labeled ω, the last letter of the Greek alphabet). These fats occur widely in nature, are key components of animal fat metabolism, and are important in both human nutrition and bodily function. The three omega‑3s relevant to human physiology are α‑linolenic acid (ALA), eicosapentaenoic acid (EPA), and docosahexaenoic acid (DHA). ALA is found in certain land plants, while DHA and EPA come from algae and fish. Marine algae and phytoplankton are the original sources of omega‑3s; fish that eat these organisms accumulate DHA and EPA. Land‑plant sources of ALA include walnuts, chia seeds, flaxseeds, and hempseed oil, whereas EPA and DHA are obtained from fish, fish oils, and algae oil.

Nearly all animals cannot make the essential omega‑3 ALA on their own and must get it from food. However, when ALA is available, animals can convert it into EPA and then DHA by adding extra double bonds (desaturation) and lengthening the carbon chain (elongation). Specifically, ALA (18 carbons, 3 double bonds) is used to produce EPA (20 carbons, 5 double bonds), which is then turned into DHA (22 carbons, 6 double bonds). This conversion ability may decline with age. When foods containing unsaturated fats are exposed to air, they are prone to oxidation and rancidity.

Evidence for omega‑3 supplements in preventing cancer, all‑cause mortality, and most cardiovascular outcomes is limited, though they do modestly lower blood pressure and reduce triglycerides. Since 2002, the U.S. Food and Drug Administration has approved four fish‑oil‑based prescription drugs for managing high triglycerides: Lovaza, Omtryg (both omega‑3‑acid ethyl esters), Vascepa (ethyl eicosapentaenoic acid), and Epanova (omega‑3‑carboxylic acids).

**History** In 1929, George and Mildred Burr discovered that fatty acids are essential for health; a lack of them in the diet led to a life‑threatening deficiency. They coined the term “essential fatty acids.” Since then, research interest in unsaturated essential fatty acids has grown because they form the basis of cell membranes. Awareness of their health benefits increased sharply after the 1980s. On 8 September 2004, the U.S. FDA granted a “qualified health claim” to EPA and DHA omega‑3s, stating that “supportive but not conclusive research shows that consumption of EPA and DHA [omega‑3] fatty acids may reduce the risk of coronary heart disease.” This updated an earlier health risk advice letter from 2001. The Canadian Food Inspection Agency recognizes DHA’s importance and allows the claim that “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.” Historically, whole‑food diets provided enough omega‑3s, but because these fats oxidize easily, the shift toward shelf‑stable processed foods has led to a deficiency in manufactured foods.

**Nomenclature** The terms ω‑3 (omega‑3) and n‑3 fatty acid come from organic chemistry naming conventions. An unsaturated fatty acid’s name can indicate the location of the double bond closest to the methyl end of the molecule. Here, n (or ω) stands for the carbon number at the methyl end, and n−x (or ω−x) gives the position of the nearest double bond. For omega‑3 fatty acids, that double bond is at carbon 3 from the methyl end. This naming system is useful because most chemical changes happen at the carboxyl end, while the methyl group and its nearest double bond remain unchanged in many reactions. In n−x or ω−x, the symbol is a minus sign, not a hyphen, though it is never read that way. The n (or ω) represents the methyl‑end carbon counted from the carboxyl end. For example, in an 18‑carbon omega‑3 fatty acid, the methyl end is at carbon 18 from the carboxyl end; n−3 (or ω−3) means 18−3 = 15, which is the location of the nearest double bond from the carboxyl end. Although n and ω are synonymous, the IUPAC recommends using n to identify the highest carbon number. Still, “omega‑3 fatty acid” is more common in both popular media and scientific literature.

**Example** α‑Linolenic acid (ALA) is an 18‑carbon chain with three double bonds, the first located at the third carbon from the methyl end, making it an omega‑3 fatty acid. Counting from the carboxyl end, the double bonds are at carbons 9, 12, and 15. These positions are often written as Δ9c, Δ12c, Δ15c, or cisΔ9, cisΔ12, cisΔ15, or cis‑cis‑cis‑Δ9,12,15, where “c” or “cis” indicates the double bonds are in the cis configuration. ALA is polyunsaturated (more than one double bond) and is also described by the lipid number 18:3, meaning 18 carbons and 3 double bonds.

**Chemistry** An omega‑3 fatty acid is a fatty acid with a specific double‑bond pattern.