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. 2019 Jan 4;11(1):89. doi: 10.3390/nu11010089

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© 2019 by the authors.

Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/).

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Pathways of long-chain polyunsaturated fatty acid biosynthesis in humans and fish. All activities other than Δ4 desaturation (Δ4 Fad) are present in humans. Similarly, all activities have been demonstrated in teleost fish species, although not all species express all activities. The presence of Δ4 Fad enabling direct production of 22:6n-3 from 22:5n-3 has only been demonstrated in a few teleost fish species and, therefore, DHA (22:6n-3) production from EPA (20:5n-3) in most fish species and humans is only possible via the Sprecher shunt [1]. Δ4 Fad, Δ5 Fad and Δ6 Fad, fatty acyl desaturases; DHA, docosahexaenoic acid; EPA, eicosapentaenoic acid; Elovl2, Elovl4 and Elovl5, fatty acid elongases. Reproduced by permission from Tocher [2].