Omega-3

ω−3 fatty acids (commonly spelled omega-3 fatty acids) are a family of polyunsaturated fatty acids which have in common a carbon-carbon double bond in the ω−3 position. more...

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Important nutritionally essential ω−3 fatty acids are: α-linolenic acid (ALA), eicosapentaenoic acid (EPA), and docosahexaenoic acid (DHA). For a more complete list, see list of ω−3 fatty acids. The human body cannot synthesize ω−3 fatty acids de novo, but it can form 20- and 22-carbon unsaturated ω−3 fatty acids from the eighteen-carbon ω−3 fatty acid, α-linolenic acid. These conversions occur competitively with ω−6 fatty acids, which are essential closely related chemical analogues that are derived from linoleic acid. Both the ω−3 α-linolenic acid and ω−6 linoleic acid are essential nutrients which must be obtained from food. Synthesis of the longer ω−3 fatty acids from linolenic acid within the body is competitively slowed by the ω−6 analogues. Thus accumulation of long-chain ω−3 fatty acids in tissues is more effective when they are obtained directly from food or when competing amounts of ω−6 analogs do not greatly exceed the amounts of ω−3.

Chemistry

For detail on ω (omega) nomenclature and numbering, see EFA Nomenclature.

The term ω−3 (aka \"n−3\", \"omega-3\") signifies that the first double bond exists as the third carbon-carbon bond from the terminal methyl end (ω) of the carbon chain.

ω−3 fatty acids which are important in human nutrition are: α-linolenic acid (18:3, ALA), eicosapentaenoic acid (20:5, EPA), and docosahexaenoic acid (22:6, DHA). These three polyunsaturates have either 3, 5 or 6 double bonds in a carbon chain of 18, 20 or 22 carbon atoms, respectively. All double bonds are in the cis-configuration, i.e. the two hydrogen atoms are on the same side of the double bond.

Biological significances

The biological effects of the ω-3 fatty acids are largely mediated by their interactions with the ω-6 fatty acids; see Essential fatty acid interactions for detail.

A 1992 article by biochemist William E.M. Lands provides an overview of the research into ω−3 fatty acids, and is the basis of this section. Extensive details of physiology, metabolism and nutrition are provided in his 2005 book, \"Fish, Omega-3 and Human Health\". A 2007 book by Evelyn Tribole, \"The Ultimate Omega-3 Diet\" extends this discussion with food contents and recipes by which people can balance dietary intakes of ω−3 and ω−6 fats.

The 'essential' fatty acids were given their name when researchers found that they were essential to normal growth in young children and animals. (Note that the modern definition of 'essential' is more strict.) A small amount of ω−3 in the diet (~1% of total calories) enabled normal growth, and increasing the amount had little to no additional benefit.

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