Are all n-3 polyunsaturated fatty acids created equal?

January 1, 2009 Human Health and Nutrition Data 0 Comments

Are all n-3 polyunsaturated fatty acids created equal?

Year: 2009
Authors: Anderson, B.M. Ma, D.W.L.
Publication Name: Lipids in Health and Disease
Publication Details: Volume 8; Pages 33-53.


N-3 polyunsaturated fatty acids have been shown to have potential beneficial effects for chronic diseases including cancer, insulin resistance and cardiovascular disease. Eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) in particular have been studied extensively, whereas substantive evidence for a biological role for the precursor, alpha-linolenic acid (ALA), is lacking. It is not enough to assume that ALA exerts effects through conversion to EPA and DHA, as the process is highly inefficient in humans. Thus, clarification of ALA's involvement in health and disease is essential, as it is the principle n-3 polyunsaturated fatty acid consumed in the North American diet and intakes of EPA and DHA are typically very low. There is evidence suggesting that ALA, EPA and DHA have specific and potentially independent effects on chronic disease. Therefore, this review will assess our current understanding of the differential effects of ALA, EPA and DHA on cancer, insulin resistance, and cardiovascular disease. Potential mechanisms of action will also be reviewed. Overall, a better understanding of the individual role for ALA, EPA and DHA is needed in order to make appropriate dietary recommendations regarding n-3 polyunsaturated fatty acid consumption. (Author's abstract)
ALA is found in leafy vegetables, walnuts, soybeans, flaxseed, and seed and vegetable oils. Both LA and ALA can be further metabolized to long chain PUFA through a series of desaturation and elongation steps. LA is metabolized to arachidonic acid (AA, 20:4n-6), while ALA can be metabolized to EPA (20:5n-3) and ultimately DHA (22:6n-3).  Both ALA and LA are converted to their respective long chain metabolites by the same set of enzymes, however the metabolic products of each pathway are structurally and functionally distinct. EPA and AA are substrates for the synthesis of a group of inflammatory mediators including thromboxanes (TX), leukotrienes (LT), and prostaglandins (PG), collectively referred to as eicosanoids. There is growing recognition of the potential heterogeneous effects of ALA, EPA and DHA, which should be considered in future experimental designs. Clarification of the relationship between n-3 PUFA and cancer at multiple time points is also needed. The potential preventative contribution of ALA, EPA and DHA during mammary or prostate gland development has yet to be detailed. The health-related effects of EPA and DHA have undergone considerable study, however the specific biological effects of ALA are largely unknown. Therefore, more work is required to identify the differential effects of ALA on cancer, insulin resistance and cardiovascular disease. The need is even more apparent, given that ALA is by far the predominant form of n-3 PUFA consumed in the typical North American diet. The authors conclude that the identification of potentially beneficial or detrimental effects of ALA intake may have a profound and widespread impact on health promotion or disease burden. (Editor's comments)

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