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  1.   The two main omega-3 fatty acids are docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA). It has been generally accepted that fish and sea foods are the best sources of omega-3 fatty acids and should be consumed 2-3 times a week, as these compounds have been suggested to reduce the risk of cardiovascular disease.[1] The main source of these omega-3 fatty acids is oily fish such as salmon, mackerel and sardines. Olive oil and some seeds and nuts such as flax seeds, chia seeds, walnuts and pumpkin seeds are also rich in alpha-linolenic acid (ALA), another omega-3 fatty acid, which the body can then convert to DHA or EPA however to a limited extent of 2-10%.[2] The perceived benefits of omega-3 fatty acids originated from the observation of Japanese and Mediterranean populations. Japanese and Mediterranean consumption of fish is high while Mediterranean diet also encourages the use of olive oil. These populations have a lower incidence of cardiovascular disease and consequently a tendency to live longer.[3]  In addition to being associated with healthier cardiac function, studies have shown omega-3 fatty acids also play a role in healthy ageing and foetal development.[2] In fact studies have demonstrated that the many beneficial attributes of omega-3 fatty acids include reduced incidence of atherosclerosis and reduced inflammation in both overweight sedentary adults and healthy older adults.[4] [5] Furthermore animal studies have also demonstrated that an increase in omega-3 fatty acid intake can reduce the risks of Alzheimer’s disease.[6] Omega-3 supplements have also been linked to a reduction of the risk of prostate cancer. [7] Despite these potentially obvious positive effects, recent evidence has emerged that questions the benefits of omega-3 fatty acids obtained from either consumption of fish or supplements.[1] Recent studies have highlighted that increased omega-3 fatty acid consumption in people already at risk of heart disease does not reduce the incidence of stroke, heart attack or death.[8] Another study also demonstrated that omega-3 fatty acids have no discernible impact on overall mortality or the incidence of cardiovascular disease or cancer.[9]  Furthermore, contrary to some studies, high levels of omega-3 fatty acids in the blood have actually been correlated with an increased risk of prostate cancer.[10] These recent findings have led some to believe that omega-3 fatty acid supplementation may actually be harmful to the body during several medical conditions. This theory comes from the fact that, like all fatty acids, omega-3 fatty acids are prone to lipid peroxidation. Lipid peroxidation is oxidative degradation of lipids, mostly of unsaturated fatty acids making up triglycerides and phospholipids. Consumption of oxidised lipids can result in increased oxidative stress, which is associated with many adverse health effects. Indeed prolonged high levels of oxidised lipids in the blood can lead to atherosclerosis.[11] [12]  Oily fish may also contain persistent organic pollutants or metals, the latter of which may facilitate the lipid peroxidation described above.[1] Furthermore, it has also been suggested that, as omega-3 supplements lack the range of nutrients such as proteins, vitamins and minerals present in whole fish, their efficacy and function may be compromised.[13] When speaking about omega-3 fatty acids consumption the issue of omega-3 to omega-6 fatty acids ratio has to be also taken into account. With the evolution and development of agriculture this ratio has shifted from 1:1 to about 1:15 which is thought to be one of the reasons for increased incidence of heart diseases and obesity. However the optimal ratio is not yet defined according to the UK Food Standards Agency and it is advised to increase the intake of omega-3 rather than focuse on decreasing the amount of omega-6 fatty acids in your diet.[14]   Omega-3 fatty acids are essential fatty acids that play a crucial role in maintaining good health. As our bodies cannot produce them, we need to obtain them from dietary sources such as oily fish and plant oils. Given the potential for reduced efficacy when eaten in its pure form, omega-3 consumption through the diet is preferable to taking omega-3 nutritional supplements. Remember to use mild temperature ways of cooking for omega-3 rich foods to avoid lipid oxidation and preserve the benefit of omega-3. Whilst some of the health benefits previously attributed to omega fatty acids may now be under scrutiny, it is apparent it may be more to do with omega-3 to omega-6 ratios than doubting omega-3 benefits and so it is still a key part of a healthy diet and potential benefits appear to outweigh the potential risks.    [1] Maehre H, et al. (2016). ω-3 Fattyω-3 Fatty Acids and Cardiovascular Diseases: Effects, Mechanisms and Dietary Relevance Acids and Cardiovascular Diseases: Effects, Mechanisms and Dietary Relevance. International Journal of Molecular Sciences, 16(9), 22636- 22661. https://dx.doi.org/10.3390%2Fijms160922636 [2]  Swanson, D. (2012). Omega-3 fatty acids EPA and DHA: health benefits throughout life. Advances in Nutrition, 3(1), 1-7. https://doi.org/10.3945/an.111.000893 [3] Tokudome, S., et al (2004). The Mediterranean vs the Japanese diet. European Journal Of Clinical Nutrition, 58, 1323. http://dx.doi.org/10.1038/sj.ejcn.1601970 [4] Sekikawa A, et al. (2008). Marine-derived n-3 fatty acids and atherosclerosis in Japanese, Japanese Americans, and Whites: a cross-sectional study. Journal of the American College of Cardiology, 52(6), 417-424. https://doi.org/10.1016/j.jacc.2008.03.047 [5] Kiecolt-glaser, J.K. (2012). Omega-3 Supplementation Lowers Inflammation in Healthy Middle-Aged and Older Adults: A Randomized Controlled Trial. Brain, Behavior, and Immunity, 26(6), 998-995. https://doi.org/10.1016/j.bbi.2012.05.011 [6] Lim G.P, et al. (2005). A diet enriched with the omega-3 fatty acid docosahexaenoic acid reduces amyloid burden in an aged Alzheimer mouse model. The Journal of Neuroscience, 25(12), 3032-3040. https://doi.org/10.1523/JNEUROSCI.4225-04.2005 [7] Augustsson K, et al.(2003). A Prospective Study of Intake of Fish and Marine Fatty Acids and Prostate Cancer. American Association for Cancer Research, 12(1), 64-67. http://cebp.aacrjournals.org/content/12/1/64 [8]  The risk and prevention study collaborative group. (2013). N–3 Fatty Acids in Patients with Multiple Cardiovascular Risk Factors. The New England Journal of Medicine, 368(1), 1800-1808. https://doi.org/10.1056/NEJMoa1205409 [9] Hooper, L. et al. (2006). Risks and benefits of omega 3 fats for mortality, cardiovascular disease, and cancer: systematic review. BMJ, 332(752) https://doi.org/10.1136/bmj.38755.366331.2F [10] Brasky, TM. et al. (2013). Plasma Phospholipid Fatty Acids and Prostate Cancer Risk in the SELECT Trial. Journal of the National Cancer Institute, 105(15), 1132-1141. https://doi.org/10.1093/jnci/djt174 [11]  Awada M, et al. (2012). Dietary oxidized n-3 PUFA induce oxidative stress and inflammation: role of intestinal absorption of 4-HHE and reactivity in intestinal cells. Journal of Lipid Research, 53(10), 2069-2080. https://doi.org/10.1194/jlr.M026179 [12] Lobo V, et al. (2010). Free radicals, antioxidants and functional foods: Impact on human health. Pharmacognosy Review, 4(8), 118-126. https://doi.org/10.4103/0973-7847.70902 [13]  He, K. (2009). Fish, Long-Chain Omega-3 Polyunsaturated Fatty Acids and Prevention of Cardiovascular Disease—Eat Fish or Take Fish Oil Supplement? Progress in Cardiovascular Diseases, 52(2), 95-114. https://doi.org/10.1016/j.pcad.2009.06.003 [14] Stanley, J., Elsom, R., Calder, P., Griffin, B., Harris, W., & Jebb, S. et al. (2007). UK Food Standards Agency Workshop Report: the effects of the dietary n-6:n-3 fatty acid ratio on cardiovascular health. British Journal Of Nutrition, 98(06). http://dx.doi.org/10.1017/s000711450784284x
  2. Fat or oil is an important part of a diet. It is primarily made up of building blocks called fatty acids (FAs). Depending on the presence of double bonds between carbon atoms in its molecule FAs can be either saturated or unsaturated. In turn unsaturated FAs may be categorised into monounsaturated (MUFAs) having one double bond available and polyunsaturated fatty acids (PUFAs) with more than one double bond.[1] Unsaturated fatty acids are often referred to as omega fatty acids due to their chemical classification into omega-3, omega-6 and omega-9 FAs. The number stands for the position of first double bond in FA molecule which in turn determines its biochemical properties. While most of the FAs are present in the human body or may be produced in it, there are two fatty acids that can not be derived from other FAs and must be consumed from dietary sources to maintain good health condition. These FAs are called Essential Fatty acids (EFA) and include alpha-linolenic (omega-3) and linoleic (omega-6) FAs.[1][2] Docosahexaenoic acid may also become essential in some conditions but normally it can be synthesized from alpha-linoleic acid.[1]  Omega FAs have many crucial roles within the body. They reduce inflammation and possess protective properties against cardiovascular disease, are essential for pregnant woman for foetal growth and brain development.[3] They are also important for these processes in infants, who obtain them from breast milk.[4] Omega-3 FAs are also involved in the formation of cell walls and help to improve circulation and oxygen uptake.[5][6]   Other benefits include the improvement of mental health and brain function.[5][7] Scientists continue to argue on the role and potency of omega FAs to fight cancer but there is no consensus yet.[6][8][9] Omega-3 FAs have been part of the human diet throughout evolution. In early times, it is thought that the ratio of omega-3 to omega-6 FAs in our diets was approximately 1:1.[10] In Western diets the ratio of omega-3 to omega-6 FAs has dramatically shifted and is now thought to be from 1:15 to 1:20, thus there is a large disparity between modern diet and our inbuilt genetic patterns.[11][12] The reason for this change over time is thought to come from the industrial revolution and development of modern agricultural and aquacultural methods including changes in animal and fish feeds. The good example is the lower omega-3 to omega-6 ratio in cultured fish species than in wild ones. Generally omega-3 content decreased in multiples in regularly consumed food products, including eggs, fish and animal meat.[2][13] It is thought that this large shift in the ratio of omega-3 to omega-6 consumed in the Western diet is a contributory factor in the increasing incidence of atherosclerosis, coronary heart disease, hypertension, obesity, collagen vascular diseases and cancer. Scientists explain this by different biochemical properties of omega-3 and -6 FAs. While the first ones contribute to anti-inflammatory and suppressive effects for many diseases, the latter have proinflammatory and prothrombotic properties. And thus omega-3 to omega-6 ratio in the diet is crucial.[2][10][11]  According to EFSA “250 mg daily intake of long chain omega-3 FAs for adults may reduce the risk of heart disease” and this amount of eicosapentaenoic acid plus docosahexaenoic acid is stated as an adequate intake level.[14] However there is no any recommendations on the omega-3/6 ratio which is surprising if to take into account the recent scientific evidence noted above.[3]   The primary sources of omega-3 FAs are vegetable oils (ALA) and marine fish oils (DHA and EPA), although minor quantities of omega-3 FAs are also found in meat, egg yolk, nuts, seeds, green leafy vegetables and some fruits.[2][15] Flaxseed oil contains 53-62% omega-3 FAs, while canola oil, walnut oil, wheat germ oil and soybean contain 7-11%.[15][16] The richest fish sources of omega-3 FAs are salmon, mackerel, herring and halibut. Raw salmon and mackerel contain 1.2% and 2.5% of omega-3 FAs, respectively.[15] Fresh fish is thought to be higher in omega-3 FAs than processed varieties as processing (especially with heating) may denature omega-3 FAs and convert them to harmful substances.[2] The changes in agriculture and food processing techniques over the last fifty years have resulted in an imbalance in the ratio of omega-3 to omega-6 FA intake. This may have a negative impact on our health, but could still be redressed by increasing consumption of foods high in omega-3 FAs. Unfortunately farmed fish and animals are not that beneficial as wild ones due to a lower omega-3 FAs content. It is also worth noting that processing decreases the contents of PUFAs in food and should preferably be reduced.   [1] Tvrzicka, E., Kremmyda, L., Stankova, B., & Zak, A. (2011). Fatty acids as biocompounds: their role in human metabolism, health and disease – a review. part 1: classification, dietary sources and biological functions. Biomedical Papers, 155(2), 117-130. http://dx.doi.org/10.5507/bp.2011.038  [2] Das, U. (2006). Essential Fatty Acids - A Review. Current Pharmaceutical Biotechnology, 7(6), 467-482. http://dx.doi.org/10.2174/138920106779116856 [3] Scientific Opinion on Dietary Reference Values for fats, including saturated fatty acids, polyunsaturated fatty acids, monounsaturated fatty acids,transfatty acids, and cholesterol. (2010). EFSA Journal, 8(3), 1461. http://dx.doi.org/10.2903/j.efsa.2010.1461 [4] Muhlhausler, B., Gibson, R., & Makrides, M. (2010). Effect of long-chain polyunsaturated fatty acid supplementation during pregnancy or lactation on infant and child body composition: a systematic review. American Journal Of Clinical Nutrition, 92(4), 857-863. http://dx.doi.org/10.3945/ajcn.2010.29495 [5] Wysoczański, T., Sokoła-Wysoczańska, E., Pękala, J., Lochyński, S., Czyż, K., & Bodkowski, R. et al. (2016). Omega-3 Fatty Acids and their Role in Central Nervous System - A Review. Current Medicinal Chemistry, 23(8), 816-831. http://dx.doi.org/10.2174/0929867323666160122114439 [6] Kremmyda, L., Tvrzicka, E., Stankova, B., & Zak, A. (2011). Fatty acids as biocompounds: their role in human metabolism, health and disease – a review. part 2: fatty acid physiological roles and applications in human health and disease. Biomedical Papers, 155(3), 195-218. http://dx.doi.org/10.5507/bp.2011.052 [7] Lin, P., Chiu, C., Huang, S., & Su, K. (2012). A Meta-Analytic Review of Polyunsaturated Fatty Acid Compositions in Dementia. The Journal Of Clinical Psychiatry, 73(09), 1245-1254. http://dx.doi.org/10.4088/jcp.11r07546 [8] Jing, K., Wu, T., & Lim, K. (2013). Omega-3 Polyunsaturated Fatty Acids and Cancer. Anti-Cancer Agents In Medicinal Chemistry, 13(8), 1162-1177. http://dx.doi.org/10.2174/18715206113139990319 [9] Fabian, C., Kimler, B., & Hursting, S. (2015). Omega-3 fatty acids for breast cancer prevention and survivorship. Breast Cancer Research, 17(1). http://dx.doi.org/10.1186/s13058-015-0571-6 [10] Simopoulos, A. (2008). The Importance of the Omega-6/Omega-3 Fatty Acid Ratio in Cardiovascular Disease and Other Chronic Diseases. Experimental Biology And Medicine, 233(6), 674-688. http://dx.doi.org/10.3181/0711-mr-311 [11] Simopoulos, A. (2016). An Increase in the Omega-6/Omega-3 Fatty Acid Ratio Increases the Risk for Obesity. Nutrients, 8(3), 128. http://dx.doi.org/10.3390/nu8030128 [12] Simopoulos, A. (2006). Evolutionary aspects of diet, the omega-6/omega-3 ratio and genetic variation: nutritional implications for chronic diseases. Biomedicine & Pharmacotherapy, 60(9), 502-507. http://dx.doi.org/10.1016/j.biopha.2006.07.080 [13] van Vliet, T., & Katan, M. (1990). Lower ratio of n-3 to n-6 fatty acids in cultured than in wild fish. Trends In Food Science & Technology, 1, 51. http://dx.doi.org/10.1016/0924-2244(90)90038-z [14] EFSA. (2010). EFSA sets European dietary reference values for nutrient intakes | European Food Safety Authority. Efsa.europa.eu. Retrieved 10 October 2017, from https://www.efsa.europa.eu/en/press/news/nda100326 [15] Kris-Etherton, P., Taylor, D., Yu-Poth, S., Huth, P., Moriarty, K., & Fishell, V. et al. (2000). Polyunsaturated fatty acids in the food chain in the United States. Am J Clin Nutr, 71(1), 179S-88S. Retrieved from https://www.ncbi.nlm.nih.gov/pubmed/10617969 [16] Hunter, J. (1990). n-3 fatty acids from vegetable oils. Am J Clin Nutr, 51(5), 809-14. Retrieved from https://www.ncbi.nlm.nih.gov/pubmed/1970702