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  1. Fish is rich in beneficial omega-3 fatty acids, though while cooking under high temperatures we may destroy any benefit of fish. But different cooking methods affect fish differently. Surprisingly, I read that frying reduces amount of heavy metals better than any other cooking method. Is it true? If so, should we opt for fried fish or still it is better to avoid it as any other fried food? 
  2. The evidence that omega-3 fatty acids (FAs) such as eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) have a cardioprotective effect is increasing, and the American Heart Association recommend consuming at least two servings of fish per week.[1] [2]  These cardioprotective benefits can be obtained by eating either farmed and wild fish, with the highest amounts of omega-3 being found in oily fish such as salmon or mackerel. They have been observed from as little as one fish meal per week and improve with every extra meal consumed up to five fish meals per week.[3] One study showed a 29% decrease in mortality in the two year period following a heart attack in patients who were advised to eat oily fish compared to those who were not.[1] In another, where over 18,000 patients with high cholesterol were observed over a five year period, those who were prescribed 1800 mg/day of EPA in addition to statins had significantly fewer coronary events than those prescribed just statins.[4] Studies have also shown that the mineral and FA content of fish are significantly affected by different cooking methods.[5] [6] One study, for example, concluded that thermal processing of tuna damages the beneficial fats contained within it.[7] In another study, a comparison of cooking methods (baking, frying and microwaving) used to prepare seabass showed that the protein content was significantly changed by all cooking methods and FA levels were generally decreased by most methods.[6] Omega-6 FA levels were shown to increase with frying and omega-3 FA levels increased with microwaving.[6] The conclusion was that to gain the optimum health benefits of FAs from fish, it should be broiled, baked or microwaved, which result in lower levels of less favourable FAs.[5] [6] [8] However, other studies have found that different cooking methods have no effect on omega-3 FA levels. Although in one study fried fish had increased levels of omega-6 FAs and monounsaturated FAs, these were attributed to the oil used for frying.[8] In addition to effects on FA content, cooking practices can also affect the levels of pollutants, such as heavy metals, present in fish. One study on hammour fish found that, although the majority of the heavy metals present were below maximum permitted levels (MPLs), the levels of lead and arsenic exceeded them.[9] Cooking methods had variable effects on pollutant levels; lead levels decreased with all cooking methods (-16.2% with roasting, -20.7% with frying and -13.2% with broiling), whilst the results for cadmium varied (no change with roasting, totally eliminated with frying and -20.7% with broiling).[9] Freezing the raw fish for six months had no significant effect.[9] Other investigations have found that various cooking methods can affect both the nutrient composition and levels of heavy metal pollutants.[10] The researchers of this study concluded that both excessive frying and the use of salt should be avoided in order to maximise the health benefits of the fish. Furthermore, in order to minimise heavy metal exposure and maximise nutritional benefit, a variety of fish species should be consumed.[10] With regards to mercury levels,a general decrease has been seen with a variety of cooking methods while some mercury can leach out into the water when the fish were boiled.[11]   Baking, boiling and frying fish have been shown to reduce endocrine-disrupting perfluorinated compounds (PFCs), for example, baking at 160oC for 15 minutes has been shown to completely remove PFCs.[12] Where radio-caesium was tested, levels appeared increased after deep frying in a study of fish caught on the Savannah River, however this was attributed to the loss of weight from the fish during cooking (i.e.increases in concentration).[13] In addition to a potential loss of nutrients and alterations in pollutant levels, cancer-promoting substances found in cooked fish are another cause for concern. Carcinogenic heterocyclic amines (HCAs) are produced during various cooking processes. The quantity of HCAs ordinarily consumed is thought to be too low to specifically cause cancer, however, in combination with other mutagens or carcinogens they can be tumour promoters. Hence, it is advisable to minimise HCAs in the diet, for example by microwaving fish instead of frying. It has also been established that supplementing the diet with soy-isoflavones suppresses breast cancer induction by HCAs.[14] Nitrosamines, another group of carcinogenic compounds are also formed during the cooking of fish.[15] This potential for the generation of carcinogenic compounds during cooking is supported by an observed direct association between white fish cooked at high temperatures (pan frying, oven broiling and grilling) and prostate cancer.[16]  However, despite these potential risks, it appears that the health benefits of omega-3 FAs and other nutrients obtained by eating fish may outweigh any associated dangers of cooking FAs rich food. However, care should be taken with the cooking method, temperature, and time. Overall baking and boiling appear to be the safest fish cooking ways. Consuming a variety of species can also decrease the risk of exposure to excessive levels of heavy metals and other pollutants while maximising nutritional benefit.   [1] Burr ML, et al. (1989) Effects of changes in fat, fish, and fibre intakes on death and myocardial re-infarction: diet and re-infarction trial (DART). Lancet, 2, 757–76 [2] Kris-Etherton PM, et al. (2002) Fish consumption, fish oil, omega-3 fatty acids, and cardiovascular disease. Circulation, 106, 2747–2757  [3] Psota TL, et al. (2006) Dietary omega-3 fatty acid intake and cardiovascular risk. Am J Cardiol, 98, 3–18 [4] Yokoyama M, et al. (2007) Japan EPA lipid intervention study (JELIS) Investigators. Effects of eicosapentaenoic acid on major coronary events in hypercholesterolaemic patients (JELIS): a randomised open-label, blinded endpoint analysis. Lancet, 369, 1090–1098  [5] Gokoglu N, et al. (2004) Effects of cooking methods on the proximate composition and mineral contents of rainbow trout. Food Chem, 84(1), 19-22 [6] Türkkan AU, et al. (2008) Effects of cooking methods on the proximate composition and fatty acid composition of seabass  (Dicentrarchus labrax, Linnaeus, 1758). Food and Bioproducts Processing, 86(3), 163-66 [7] Aubourg S, et al. (1995) A comparison between conventional and fluorescence detection methods of cooking-induced damage to tuna fish lipids. European Food Res Technol, 200(4), 252-55 [8] Neff MR, et al. (2014) Effects of different cooking methods on fatty acid profiles in four freshwater fishes from the Laurentian Great Lakes region. Food Chem, 164, 544-50 [9] Ganbi, HHA. (2010) Heavy metals pollution level in marine hammour fish and the effect of popular cooking methods and freezing process on these pollutants. World J Dairy Food Sci, 5(2), 119-126 [10] Musaiger AO & D’Souza R. (2008) The effects of different methods of cooking on proximate, mineral and heavy metal composition of fish and shrimps consumed in the Arabian Gulf. Arch Latinoam Nutr, 58(1), 103-9 [11] Miero CL, et al. (2016) Fish and mercury: influence of fish fillet culinary practices on human risk. Food Control, 60, 575-81 [12] del Gobbo L, et al. (2008) Cooking decreases observed perfluorinated compound concentrations in fish. J Agric Food Chem, 55(16), 7551-9 [13] Burger J, et al. (2004) Effects of cooking on radiocesium in fish from the Savannah River: exposure differences for the public. Faculty Research & Creative Activity. Paper 60. [14] Sugimara T, et al. (2004) Heterocyclic amines: mutagens/carcinogens produced during cooking of meat and fish. Cancer Sci, 95(4), 290-99 [15] Huang DP, et al. (1981) Volatile nitrosamines in salt-preserved fish before and after cooking. Food and Cosmetics Toxicology, 19, 167-71 [16] Joshi AD, et al. (2012) Fish intake, cooking practices, and risk of prostate cancer: results from a multi-ethnic case-control study. Cancer Causes Contr, 23(3), 405-20  
  3.   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
  4. Drug interactions occur when the effect of a drug is altered if taken in conjunction with another drug, supplement, food, or alcohol. Drugs can interact with dietary supplements either directly or indirectly, increasing or decreasing the drug’s desired effects. Indirect effects can result from changes in excretion,  metabolism or, occasionally, absorption of the substance, which can result in reduced or increased pharmacological activity of the drug. This can trigger unexpected and potentially harmful side effects. These interactions can occur in numerous ways, from the way different substances react with each other in the stomach, to the mechanism of metabolism in the body. Such interactions can vary between subjects, as everyone’s body is different in terms of its ability to absorb, metabolise, distribute and excrete drugs and their metabolites. There are several factors that can lead to these differences, including genetic variation, body weight (hence why some drugs are dosed according to this), age, gender (often due to hormone levels), drug tolerance and even diet. An example of the latter is the reduced response to bronchodilators associated with a high-fat diet.[1] Because of these variations, drug interactions can be difficult to predict, even when their reactions are well-known.  Western populations consume an ever-increasing amount of dietary supplements, including vitamins, minerals, herbs and many other products. These can come in many forms, such as pills, capsules, powders, drinks and energy bars. Adverse reactions between supplements and prescribed medications are well documented: warfarin, insulin and aspirin, for instance, have a high record of adverse interactions with dietary or herbal supplements.[2] Mixing warfarin and fish oil, for example, can lead to uncontrolled bleeding, while insulin combined with chromium can induce hypoglycaemia in diabetics.[2] The increasing number of dietary supplements available, coupled with the fact that they are not as well-regulated as medicinal products, means the potential for adverse interactions is escalating. Consumers tend to assume that because dietary supplements are so readily available, they must be safe – a belief enhanced by the liberal use of the word ‘natural’ in association with these products. However, their safety is not necessarily assured, and their combined use with certain drugs can result in serious adverse reactions. Commonly used supplements such as vitamin E, ginseng and gingko biloba have all been touted for their ability to boost certain health aspects, but they also interact with various widely prescribed drugs, causing life-threatening reactions such as reduced blood clotting, psychosis, hypoglycaemia and even coma.[2] It is not just adverse reactions that are of concern when combining supplements and drugs. Interactions can also reduce a drug’s effectiveness, such as the interaction seen between St. John’s wort and oral contraceptive pills.[3] Consumers should always think carefully when choosing dietary supplements, especially those who are taking medications. The combination could potentially be lethal – a far cry from the aim of trying to improve your health. Always consult your doctor before taking a supplement or changing your medication regimen.   [1] Wood LG, Garg ML, Gibson PG (2011). A high-fat challenge increases airway inflammation and impairs bronchodilator recovery in asthma. J Allergy Clin Immunol. 127(5). 1133-40. [2] Gardiner P, Phillips R, Shaughnessy AF (2008). Herbal and dietary supplement-drug interactions in patients with chronic illnesses. Am Fam Physician. 77(1). 73-8. [3] Murphy PA, Kern SE, Stanczyk FZ, Westhoff CL (2005). Interaction of St. John's Wort with oral contraceptives: effects on the pharmacokinetics of norethindrone and ethinyl estradiol, ovarian activity and breakthrough bleeding. Contraception. 71(6). 402-8.  
  5. What is healthy salmon Salmon is renowned for its health benefits, as it is high in omega-3 and -6, which are essential fatty acids (EFAs). Omega-3- and -6 are polyunsaturated EFAs that play vital roles within the human body.  It is thought that increasing polyunsaturated EFA consumption can reduce the risk of many diseases, including heart disease, multiple sclerosis and a variety of mental disorders. As many people are deficient in omega 3,[1] eating ‘oily’ fish such as salmon is one potential way to help increase omega-3 levels and to reduce the incidence of such diseases. Less than half the world’s salmon comes from the fish’s natural wild environment, with the rest coming from fish farms, also known as aquacultures.[2] Although wild salmon is still available, global stocks have been in decline for decades. Aquaculture on the other hand continues to flourish, with 90.4 million tonnes of farmed fish produced in 2012 alone.[3] Whilst wild salmon feed on their natural prey (other living organisms), farmed salmon are fed fat-rich commercial feeds. There are therefore some important differences in their nutritional composition; for example, farmed salmon has almost three times the fat content of wild salmon, a large constituent of which are EFAs.[4][5] It might be easy to assume that an increased EFA content might mean that farmed salmon are more beneficial to our health, however this is also coupled with an increased omega-6/omega-3 ratio.[4] In order to gain the main benefits of EFA consumption, omega-6 and -3 intake needs to be balanced. Many people today are consuming too much omega-6 relative to omega-3, which distorts this balance and negates some of the beneficial effects of EFA consumption. It has been speculated that the negative effects of an increased omega-6/omega-3 ratio in humans are due to increased inflammation within the body, and furthermore that it may play a role in the increased incidence of chronic diseases such as heart disease.[6] In addition to differing nutritional compositions, farmed and wild salmon contain varying levels of contaminants. Whilst wild fish do accumulate contaminants, farmed salmon contain much higher levels, which originate from their feed and contaminations of their environment.[7] [8] Studies have shown that the levels of contamination can vary depending on the geographical location of the farm. One study showed that European farms have more contaminants than American farms, with farms in Chile seeming to have the least.[7] These contaminants include polychlorinated biphenyls (PCBs), polybrominated diphenylethers (PBDEs), dioxins, and several chlorinated pesticides.[7] [8] Some of the most dangerous of these contaminants are PCBs, which have been strongly associated with cancer and other health problems.[9] Studies have shown that this PCB contamination can occur directly from farmed salmon feed,[8] [10] with one investigation of salmon from worldwide origins demonstrating that farmed salmon had almost ten time the PCB levels of wild salmon (51,216 vs 5,302 pg/g).[8] The study suggested that the cancer-risks associated with consuming these contaminants may potentially outweigh the benefits of EFA consumption. Evidence regarding contamination with trace element is a little more conflicting: arsenic levels have been found to be higher in farmed salmon, but levels of cobalt, copper and cadmium higher in wild salmon.[11] Given the lower levels of contamination and the reduced omega-6/omega-3 ratio in wild salmon compared to farmed salmon, it seems that wild salmon would be the safest option for your table, particularly when considering the benefits of polyunsaturated EFA consumption. However, as with all constituents of a balanced diet, intake should be moderated to avoid the potential ill effects of overconsumption.     [1] Simopoulos, AP. (2013) Dietary omega-3 fatty acid deficiency and high fructose intake in the development of metabolic syndrome, brain metabolic abnormalities, and non-alcoholic fatty liver disease. Nutrients. 5(8). 2901-23. [2]Foran, JA. et al. (2005) Quantitative analysis of the benefits and risks of consuming farmed and wild salmon. J Nutr. 135(11). 2639-43. [3] FAO (2014) The State of World Fisheries and Aquaculture. Retrieved April 2016 from, http://www.fao.org/3/a-i3720e.pdf [4] Hamilton, MC. et al. (2005) Lipid composition and contaminants in farmed and wild salmon. Environ Sci Technol. 39(22). 8622-9.   [5]Blanchet, C. et al. (2005) Fatty acid composition of wild and farmed Atlantic salmon (Salmo salar) and rainbowtrout (Oncorhynchus mykiss). Lipids. 40(5). 529-31.   [6]Simopoulos, A. (2006) Evolutionary aspects of diet, the omega-6/omega-3 ratio and genetic variation: nutritional implications for chronic diseases. Biomed Pharmcother. 60(9). 502-7.   [7] Hites, RA. et al. (2004) Global assessment of polybrominated diphenyl ethers in farmed and wild salmon. Environ Sci Technol. 38(19). 4945-9. [8] Easton, MDL. et al. (2002) Preliminary examination of contaminant loadings in farmed salmon, wild salmon and commercial salmon feed. Chemosphere. 46(7). 1053-74. [9] Foran, JA. et al. (2005) Risk-based consumption advice for farmed Atlantic and wild Pacific salmon contaminated with dioxins and dioxin-like compounds. Environ Health Perspect. 113(5). 552-6. [10] Carlson, DL. & Hites, RA. (2005) Polychlorinated biphenyls in salmon and salmon feed: global differences and bioaccumulation. Environ Sci Technol. 39(19). 7389-95. [11] Foran, JA. et al. (2004) A survey of metals in tissues of farmed Atlantic and wild Pacific salmon. Environ Sci Technol. 23(9). 2108-10.