Research Review By Jessica Sleeth©

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Date Posted:

January 2011

Study Title:

Fatty acids from fish: the anti-inflammatory potential of long-chain omega-3 fatty acids

Authors:

Wall R, Ross RP, Fitzgerald GF et al.

Author's Affiliations:

Alimentary Pharmabiotic Centre, County Cork, Ireland; Food Research Centre, Fermoy, County Cork, Ireland; University College Cork, National University of Ireland, Ireland.

Publication Information:

Nutrition Reviews 2010; 68(5): 280-289.

Background Information:

Polyunsaturated fatty acids (PUFAs) influence numerous functions in the body, including blood pressure regulation, blood clotting, and development and function of the brain and nervous system (1). The focus of this review is the role that PUFAs play in regulating the body’s inflammatory response. Eicosanoids, which are signaling molecules produced from 20-carbon PUFAs, have an important role in regulating the duration and intensity of the inflammation response (2). Linoleic acid (precursor to omega-6 fatty acid) and α-linolenic acid (precursor to omega-3 fatty acid) are frequently highlighted in nutrition research as they are the only two PUFAs that the human body requires, yet cannot produce.

The recommended ratio of omega-6:omega 3 fatty acids is 4:1, however many North American diets consist of intakes in excess of 16:1 (3). Researchers speculate that excess linoleic acid may be the result of increased consumption of vegetable oils, which are very prevalent in North American diets (3). As linoleic acid consumption has increased, the rate of several diseases associated with inflammation regulation have increased – specifically, cardiovascular diseases, inflammatory diseases, obesity, cancer, and depression (4).

The authors of this review paper discussed the literature dealing with the anti-inflammatory effects of omega-3 fatty acid intake and how they can affect disease processes.

Summary:

High omega-6 fatty acid consumption, particularly when viewed as a ratio of omega-6 to omega-3 intake, is typical of North American diets (the ideal n-6:n-3 ratio is 4:1). This dietary pattern is associated with the increased incidence of inflammatory diseases, as it promotes increased production of prostaglandin E2 (PGE2) and leukotriene B1 (LTB1) - both are eicosanoids derived from arachidonic acid (an omega-6 fatty acid) (5). Increased consumption of the omega-3 fatty acids EPA (eicosapentaenoic acid) and DHA (docosahexaenoic acid), either through supplementation or fish consumption, can help to decrease the inflammatory response as they are known to alter the body’s immune response (6). This has been well documented.

Many clinical trials have been conducted to investigate the relationship between omega-3 fatty acids and chronic inflammatory disorders, such as rheumatoid arthritis (7) and irritable bowel disease (IBD) (8). The trials have shown that consumption of omega-3 fatty acids can regulate the body’s immune response by modifying the production of eicosanoids and decreasing levels of proinflammatory cytokines (2). Increased consumption of omega-6 fatty acids has been correlated with the increased incidence of IBD in North America. Therefore, modifying the ratio of omega-3 fatty acids to omega-6 fatty acids may be important in the regulation of IBD (9).

In a study conducted by Belluzzi et al. (1996) (10), patients with Crohn’s disease who were in remission were randomized to receive either a placebo or 2.7g of omega-3 fatty acids per day (in the form of a fish oil supplement). After one year, 28% of the supplement group and 69% of the placebo group had relapsed (results were statistically significant). Further, 59% of the supplement group compared to 26% of the placebo group remained in remission at one year post-trial (10).

As previously noted, unregulated inflammation is associated with other diseases such as the spectrum of cardiovascular diseases and Alzheimer’s disease. Many years ago, a study by Bang and Dyerberg (1976) (11), profiling a Greenland Eskimo population, established that their diet, which is high in omega-3 fatty acids, has a protective effect from cardiovascular diseases. Numerous other studies highlighting diets rich in omega-3 fatty acids also demonstrate protective effects against cardiovascular diseases. Several studies referenced by Wall et al. (2010) investigate whether omega-3 fatty acids have a preventive effect with Alzheimer’s disease. The mechanism behind this proposed effect involves DHA, one of the primary fatty acids in the brain. DHA is a critical component for neural development, intelligence, and maintenance of cognition. The authors’ review of the research suggests that consumption of omega-3 fatty acids may decrease the risk of developing Alzheimer’s disease and potentially slow disease progression. More research is required in this area.

Clinical Application & Conclusions:

North American diets generally consist of an excess of omega-6 fatty acids, which may increase the body’s inflammatory response. Increased dietary consumption of omega-3 fatty acids modifies the body’s inflammatory response and is associated with prevention and/or remission of certain inflammatory diseases such as IBD, cardiovascular diseases, rheumatoid arthritis, and Alzheimer’s disease.

Dietary recommendations for optimal health include linoleic acid, α-linolenic acid, EPA, and DHA. The recommended ratio for omega-6 to omega-3 fatty acids is 4:1. Main dietary sources of linoleic acid (omega-6) are sunflower, safflower, and corn oils, animal fat, wholegrain bread, and cereals. The main dietary sources of α-linolenic acid (omega-3) are green leafy vegetables, flaxseed, and rapeseed oils. Salmon, trout, and herring are examples of fish higher in EPA and DHA (omega-3 fatty acids).

Many health organizations recommend increased consumption of omega-3 fatty acids (particularly, DHA and EPA); however, consistent and widely accepted recommendations of the amount required for therapeutic effect or primary prevention are not currently available.

Study Methods:

This paper was a narrative review of the literature and as such, no formal methods were provided. This format was appropriate for the topic of discussion.

Additional References:

  1. Das, UN. Biological significance of essential fatty acids. J Assoc Physicians India. 2006;54:309-319.
  2. Calder, PC. n-3 polyunaturated fatty acids, inflammation, and inflammatory diseases. Am J Clin Nutr. 2006;83:1505-1519.
  3. Simopoulos AP. Importance of the ratio of omega-6/omega-3 essential fatty acids: evolutionary aspects. World Rev Nutr Diet. 2003;92:1-22.
  4. Simopoulos, AP, Leaf A., Salem, N. Workshop statement on the essentiality of and recommended dietary intakes for omega-6 and omega-3 fatty acids. Prostaglandins Leukot Essent Fatty Acids. 2000;63:119-121.
  5. James, MJ, Gibson, RA, Cleland LG. Dietary polyunsaturated fatty acids and inflammatory mediator production. Am J Clin Nutr. 2000;71(Suppl):S343-S348
  6. Simopoulos AP. Essential fatty acids in health and chronic diseases. Forum Nutr. 2003;56:67-70.
  7. Calder PC. Session 3: Joint Nutrition Society and Irish Nutrition and Dietetic Institute Symposium on “Nutrition and autoimmune disease” PUFA, inflammatory processes and rheumatoid arthritis. Proc Nutr Soc. 2008;67:409-418.
  8. Calder, PC. Polyunsaturated fatty acids, inflammatory processes and inflammatory bowel diseases. Mol Nutr Food Res. 2008;52:885-897.
  9. Shoda R, Matsueda, K, Yamato S, Umeda N. Epidemiologic analysis of Crohn disease in Japan: increased dietary intake of n-6 polyunsaturated fatty acids and animal protein relates to the increased incidence of Crohn disease in Japan. Am J Clin Nutr. 1996;63:237-259.
  10. Belluzzi A, Brignola C, Campieri M, Pera A, Boschi S, Migliolo M. Effect of an enteric-coated fish-oil preparation on relapses in Crohn’s disease. N Engl J Med. 1996;334:1557-1560.
  11. Bang HO, Dyerberg J. Lipid metabolism and ischemic heart disease in Greenland Eskimos. Acta Med Scand. 1976;200:69-73.