Alternative Origins for Omega-3 Fatty Acids in the Diet
Fish and seafood are important sources for LC PUFAs, EPA and DHA. These fatty acids may be synthesised in the body from short-chain fatty acids, including ALA; however, the enzymes involved in this pathway are considered inefficient. This means direct EPA
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Georgia Lenihan-Geels and Karen S. Bishop
Abbreviations
ALA DHA EPA FA FADS FAO IMF LD LA LC PUFA NOS3 SC SDA USA
Alpha-linolenic acid Docosahexaenoic acid Eicosapentaenoic acid Fatty acid Fatty acid desaturase Food and Agricultural Organization of the United Nations Intramuscular fat Linkage disequilibrium Linoleic acid Long-chain polyunsaturated fatty acids Nitric oxide synthase Short-chain Stearidonic acid United States of America
Introduction Omega-3 fatty acids are found in an array of plant and animal sources. Alpha-linolenic acid (ALA), the shortest fatty acid within the omega-3 fatty acid chain (Fig. 34.1), is present in an array of foods including flaxseed, walnuts and other vegetable seeds oils as well as fish, meat and poultry [1]. The subsequent fatty acids of the omega-3 pathway (Fig. 34.1) are less abundant but can also be found in some plant seed oils, fish and meat flesh [2, 3]. Omega-3 fatty acids, in combination with other unsaturated fatty acids, maintain the fluidity of the cell membrane and may be cleaved by enzymes such as phospholipase A2, cyclooxygenase and lipooxygenase, activating inflammatoryassociated pathways [4]. Importantly, the length and extent of unsaturation of omega-3 fatty acids affects these inflammatoryassociated processes within cells. Anti-inflammatory mediators G. Lenihan-Geels (&) Nutrition, Metabolism and Genomics, Wageningen University and Research Centre, Droevendaalsesteeg 4, 6708PB Wageningen, The Netherlands e-mail: [email protected] K.S. Bishop Auckland Cancer Society Research Centre, Faculty of Medical & Health Sciences, University of Auckland, Private Bag 92019, 1142 Auckland, New Zealand e-mail: [email protected]
are cleaved from omega-3 fatty acids, while omega-6 fatty acids provide precursors for pro-inflammatory metabolites [4]. Presently, a majority of the health benefits associated with omega-3 fatty acids are attributable to the long-chain polyunsaturated fatty acids (LC PUFA), eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) [5]. The discovery of the importance of marine omega-3 fatty acids began in the 1970’s following the observation of low rates of coronary atherosclerosis among Greenland Eskimos consuming a diet high in fish and whale blubber [6, 7]. These LC PUFA have shown health-promoting effects in regard to chronic inflammation, dyslipidaemia, allergic disease and some cancers [8–12]. The current dietary recommendations for fish-derived omega-3 fatty acids is 0.25 g per day of EPA plus DHA [13]. Marine LC PUFAs, EPA and DHA, are synthesised from shorter chain omega-3 fatty acids by desaturation and elongation by specific enzymes (Fig. 34.1). Although humans produce the enzymes required for these conversions, two enzymes in this pathway are insufficient, meaning direct sources of EPA and DHA are important [14]. Marine fish feed on algae, the primary producers of LC PUFA. As fish higher up in the food chain eat these fish, there is an accumulation of LC PUFA within fish flesh. Therefore, fish are a major dietary source of LC PUFA
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