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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. Recently I came across strange article claiming that some unsaturated fatty acids are not beneficial and even dangerous to human, especially it relates to omega-3 fatty acids. I firstly thought that article was written just to attract attention, and there is not a word of truth, just stupid fabrication. But then I found another similar article in a science journal by chance, though I am no scientist and just having browsed the net. So I wonder if this is a myth or a true fact?
  4.   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
  5. Good fats vs bad fats

    Fats in our diet are a valuable source of energy (1 g is equivalent to 9 kcal), and they are essential in a healthy balanced diet. While some fats are beneficial, others, if consumed in excessive amounts, have detrimental effects on health. Fats are classified by their chemical structure, falling into several groups including saturated fats, mono-/polyunsaturated fats and trans fats. The fatty acid chains in saturated fats consist of only single bonds, indicating that there are no bonds available for further binding.[1] Foods that contain high levels of saturated fat include whole milk, butter, cheese, lard, palm oil, coconut oil, “fatty” meat and meat products, fried food, and some cakes, biscuits and pastries. All of the above should be eaten in small amounts as saturated fats have a proven association with increased cholesterol levels, which can progress to clogged arteries and increased risk of heart disease and stroke.[2] There have been numerous studies confirming the benefits of reducing saturated fats in our diets. For example, replacing saturated fats with unsaturated fats reduces cholesterol levels, thus decreasing the risks of heart disease and stroke.[2], [3] Both epidemiological and randomised clinical trials have consistently evidenced that replacing saturated fat with unsaturated fat, is beneficial in coronary heart disease.[4]    The fatty acid chains in unsaturated fats contain either one double bond (monounsaturated fat) or more than one double bond (polyunsaturated fat).[1] Foods rich in these types of fats include vegetable oils such as olive, rapeseed or sunflower oils, avocados, nuts and seeds. It has been demonstrated these fats help decrease the risk of heart disease.[5], [6] Omega-3 fatty acids are a group of polyunsaturated fats found mainly in oily fish such as mackerel, salmon or sardines. Omega-3 fatty acids have many health benefits, and are associated with good heart health as they reduce the risk of blood clots and assist in the regulation of heart rhythm.[7], [8] They are also important during pregnancy and breastfeeding, supporting infant development.[7], [8] Trans-fats are the most harmful to our bodies. This group of fats are manufactured by partially hydrogenating vegetable oils, resulting in a firmer, better tasting fat with an increased shelf life. They are found in most processed and ‘fast’ foods, that are already very high in saturated fats.[9] Manufactured trans-fats have been shown to have an even more adverse impact on cholesterol levels than saturated fats, which in turn is associated with diabetes and cardiovascular disease.[10], [11]   Whilst knowing which fats are more healthy than others can certainly help in reducing the risks associated with fat consumption, some fats can actually become more harmful during cooking, depending on the processes involved. Vegetable oil, for example can accumulate by-products known to pose a significant risk of cardiovascular disease when heated repeatedly.[12] Cooking can also change the ratio of healthier unsaturated fatty acids to unhealthy saturated fats and trans fats.[13] Reducing fat in the diet is advisable to prevent obesity and its related complications, such as type 2 diabetes. Even beneficial mono-/polyunsaturated fats should be consumed in moderation, as they still have a high calorific value. In fact studies on mice have shown that a high fat diet induces greater weight gain than a low fat diet, even if their calorific intake is the same.[14]   A reduction of saturated and trans-fats in the diet can be achieved by avoiding processed and ‘fast’ foods as much as possible and choosing food prepared at home from fresh, low fat ingredients. Lean sources of protein, low fat dairy foods, legumes, fresh fruit and vegetables are a healthier choice than foods high in fat, although beneficial oils such as olive, canola and sunflower oil can be used for cooking and salad dressings. [1] Nelson, D & Cox, M. (2008). Lehninger principles of biochemistry. (5 ed.) [2] Jakopsen, M.U. (2009). Major types of dietary fat and risk of coronary heart disease: a pooled analysis of 11 cohort studies. The American Journal of Clinical Nutrition. 85(5). 1425-1432 [3] Mozaffarian, D. et al. (2010). Effects on coronary heart disease of increasing polyunsaturated fat in place of saturated fat: a systematic review and meta-analysis of randomized controlled trials. PLos Med. 7(3). e1000252 [4] Siri-tarino, P.W. et al. (2010). Saturated fatty acids and risk of coronary heart disease: modulation by replacement nutrients. Current atherosclerosis reports. 12(6). 384-390 [5] Covas, M.I. (2007). Olive oil and the cardiovascular system. Nutritional Pharmacology. 55(3). 175-186 [6] Gillingham, L.G. et al. (2011). Dietary monounsaturated fatty acids are protective against metabolic syndrome and cardiovascular disease risk factors. Lipids. 46(3). 209-228 [7] Swanson, D. et al. (2012). Omega-3 fatty acids EPA and DHA: health benefits throughout life. Advances in Nutrition. 3(1). 1-7 [8] Calder, P.C. et al. (2009). Omega-3 polyunsaturated fatty acids and human health outcomes. BioFactors. 35(3). 266-272 [9] Stender, S. et al. (2006). A trans world journey. Atherosclerosis Supplements, 7(2), 47-52. [10] Micha, R. et al. (2009). Trans fatty acids: effects on metabolic syndrome, heart disease and diabetes. Nature Reviews: Endocrinology. 5(6). 335-344 [11] Bhardwaj, S. et al. (2011). Overview of trans fatty acids: Biochemistry and health effects. Diabetes & Metabolic Syndrome: Clinical Research & Reviews. 5(3). 161-164 [12] Ng, CY. et al. (2014) Heated vegetable oils and cardiovascular disease risk factors. Vascul Pharmacol. 61(1). 1-9 [13] Bhardwaj, S. et al. (2016) Effect of heating/reheating of fats/oils, as used by Asian Indians, on trans fatty acid formation. Food Chem. 212. 663-70 [14] Petro, A.E. et al. (2004). Fat, carbohydrate, and calories in the development of diabetes and obesity in the C57BL/6J mouse. Metabolism: clinical and experimental. 53(4). 454-457