|Types of fats in food|
Polyunsaturated fats are lipids in which the constituent hydrocarbon chain possesses two or more carbon–carbon double bonds. Polyunsaturated fat can be found mostly in nuts, seeds, fish, algae, leafy greens, and krill. "Unsaturated" refers to the fact that the molecules contain less than the maximum amount of hydrogen. These materials exist as cis or trans isomers depending on the geometry of the double bond.
Saturated fats have hydrocarbon chains which can be most readily aligned. The hydrocarbon chains in trans fats align more readily than those in cis fats, but less well than those in saturated fats. This means that, in general, the melting points of fats increase from cis to trans unsaturated and then to saturated. See the section on chemical structure of fats for more information.
The position of the carbon-carbon double bonds in carboxylic acid chains in fats is designated by Greek letters. The carbon atom closest to the carboxyl group is the alpha carbon, the next carbon is the beta carbon and so on. In fatty acids the carbon atom of the methyl group at the end of the hydrocarbon chain is called the omega carbon because omega is the last letter of the Greek alphabet. Omega-3 fatty acids have a double bond three carbons away from the methyl carbon, whereas omega-6 fatty acids have a double bond six carbons away from the methyl carbon. The illustration below shows the omega-6 fatty acid, linoleic acid.
While it is the nutritional aspects of polyunsaturated fats that are generally of greatest interest, these materials do also have non-food applications. Drying oils, which polymerize on exposure to oxygen to form solid films, are polyunsaturated fats. The most common ones are linseed (flax seed) oil, tung oil, poppy seed oil, perilla oil, and walnut oil. These oils are used to make paints and varnishes.
In preliminary research, omega-3 fatty acids in algal oil, fish oil, fish and seafood have been shown to lower the risk of heart attacks. Ongoing research indicates that omega-6 fatty acids in sunflower oil and safflower oil may also reduce the risk of cardiovascular disease.
Among n-3 fatty acids [Omega-3], neither long-chain nor short-chain forms were consistently associated with breast cancer risk. High levels of docosahexaenoic acid (DHA), however, the most abundant n-3 PUFA [Omega-3] in erythrocyte (red blood cell) membranes, were associated with a reduced risk of breast cancer. The DHA obtained through the consumption of polyunsaturated fatty acids is positively associated with cognitive and behavioral performance. In addition DHA is vital for the grey matter structure of the human brain, as well as retinal stimulation and neurotransmission.
The importance of the ratio of omega-6/omega-3 essential fatty acids as established by comparative studies shows an Omega-6:Omega-3 ratio under 4:1 may contribute to health. 
There are conflicting associations between dietary factors and incident atrial fibrillation (AF). A 2010 study published in AJCN suggested that polyunsaturated fats were found to have no significant association with AF.
Contrary to conventional advice, an evaluation of evidence from 1966-1973 pertaining to the health impacts of replacing dietary saturated fat with polyunsaturated fat found that participants in the group doing so had increased rates of death from all causes, coronary heart disease, and cardiovascular disease. Although this evaluation was criticized by many scientists, it fueled debate over worldwide dietary advice to substitute polyunsaturated fats for saturated fats. Furthermore, polyunsaturated fats (along with partially hydrogenated fats, fried foods, and smoking) are implicated in a massive increase of sphingomyelin, a oxysterol which clogs arteries and weakens muscle contraction.
Consumption during pregnancy
Consumption of omega-3 fatty acids during pregnancy is critical to fetal development. They are required during the prenatal period for the formation of synapses and cell membranes. These processes are also essential in postnatal human development for injury response of the central nervous system and retinal stimulation.
A study published in The Journal of Nutrition in 2007 found that the maternal diet of rats affects the brain DHA status of offspring. It suggests that a maternal diet containing insufficient amounts of omega-3 polyunsaturated fatty acid can lead to greater risk of decreased accretion of brain DHA in offspring.
Relation to cancer
A 2010 study of 3,081 women suffering from breast cancer was done to research the effects of polyunsaturated fats on breast cancer. It demonstrated that the consumption of high amounts of long chain omega-3 polyunsaturated fats from food produced a 25% reduced risk of additional breast cancer events. These women were also shown to have reduced risk of “all-cause mortality.” Consumption of polyunsaturated fats through fish oil supplements was not shown to decrease risk of recurring breast cancer events, although the authors noted that consumption of supplements among the group was low, less than 5%.
At least one study in mice has shown that consuming high amounts of polyunsaturated fat (but not monounsaturated fat) may increase the risk of metastasis in cancer patients. The researchers found that linoleic acid in polyunsaturated fats produced increasing membrane phase separation, and thereby increased adherence of circulating tumor cells to blood vessel walls and remote organs. According to the report 'The new findings support earlier evidence from other research that consuming high amounts of polyunsaturated fat may increase the risk of cancer spreading'. The propensity for polyunsaturated fats to oxidize is another possible risk factor. This leads to the generation of free radicals and eventually to rancidity. Studies have shown that low dosages of Coenzyme Q10 reduce this oxidation, and a combination of a diet rich in polyunsaturated fatty acids and Coenzyme Q10 supplementation leads to a longer lifespan in rats. Studies on animals have shown a link between polyunsaturated fat and the incidence of tumours. In some of these studies the incidence of tumours increased with increasing intake of polyunsaturated fat, up to about 5% of total energy, near to the middle of the current dietary intake in humans. It is advised that the level of polyunsaturated fats in the diet be regulated if Coenzyme Q10 supplements are not being taken. However, even without Coenzyme Q10 supplementation, the effect on health might be considered by some to be more beneficial than harmful, due to the supposed cholesterol lowering effects of unsaturated fats compared to saturated fats; however, (a) monounsaturated fats have also been posited to lead to lower cholesterol levels; and (b) it is no longer clear that saturated fats actually cause elevated blood cholesterol levels. See saturated fat and cardiovascular disease controversy.
Food sources of polyunsaturated fat
|Food source (100g)||Polyunsaturated fat (g)|
|Avocado Oil||13.5 |
|Whole Grain Wheat||9.7|
- Ordman, R. (2011). "Introduction to fats. Unpublished manuscript". Beloit, WI: Biochemistry Program, Beloit College.
- Wyn Snow (30 April 2004). "Chemical and Physical Structure of Fatty Acids". Retrieved 2 May 2012.
- National Institute of Health (August 1, 2005). "Omega-3 fatty acids, fish oil, alpha-linolenic acid". Archived from the original on 3 May 2006. Retrieved 26 March 2006.
- Willett, Walter C (September 2007). "The role of dietary n-6 fatty acids in the prevention of cardiovascular disease". Journal of Cardiovascular Medicine 8: S42–5. doi:10.2459/01.JCM.0000289275.72556.13. PMID 17876199.
- Pala, V.; Krogh, V; Muti, P; Chajès, V; Riboli, E; Micheli, A; Saadatian, M; Sieri, S; Berrino, F (July 2001). "Erythrocyte membrane fatty acids and subsequent breast cancer: a prospective Italian study". Journal of the National Cancer Institute 93 (14): 1088–95. doi:10.1093/jnci/93.14.1088. PMID 11459870.
- Van De Rest, O.; Geleijnse, J. M.; Kok, F. J.; Van Staveren, W. A.; Dullemeijer, C.; Olderikkert, M.G.M.; Beekman, A. T.F.; De Groot, C. P.G.M. (August 2008). "Effects of Fish Oil on cognitive performance in older subjects". Neurology 71 (6): 430–38. doi:10.1212/01.wnl.0000324268.45138.86. PMID 18678826.
- Bain, S. (2010). "Achieving optimal omega-3 atty actid status in the vegan population". Beloit, WI: Biochemistry Program.
- Veldink, J H; Kalmijn, S; Groeneveld, G-J; Wunderink, W; Koster, A; De Vries, J H M; Van Der Luyt, J; Wokke, J H J; Van Den Berg, L H (April 2007). "Intake of polyunsaturated fatty acids and vitamin E reduces the risk of developing amyotrophic lateral sclerosis". Journal of Neurology, Neurosurgery, and Psychiatry 78 (4): 367–71. doi:10.1136/jnnp.2005.083378. PMC 2077791. PMID 16648143.
- Okamoto, Kazushi; Kihira, Tameko; Kondo, Tomoyoshi; Kobashi, Gen; Washio, Masakazu; Sasaki, Satoshi; Yokoyama, Tetsuji; Miyake, Yoshihiro et al. (October 2007). "Nutritional status and risk of amyotrophic lateral sclerosis in Japan". Amyotrophic Lateral Sclerosis 8 (5): 300–4. doi:10.1080/17482960701472249. PMID 17852010.
- Simopoulos (October 2002). "The importance of the ratio of omega-6/omega-3 essential fatty acids". The importance of the ratio of omega-6/omega-3 essential fatty acids (National Institutes of Health) 56 (8): 365–79. doi:10.1016/S0753-3322(02)00253-6. PMID 12442909.
- Bain, S. (2010). "Achieving optimal omega-3 fatty acid status in the vegan population". Beloit, WI: Biochemistry Program.
- Shen, J.; Johnson, V. M.; Sullivan, L. M.; Jacques, P. F.; Magnani, J. W.; Lubitz, S. A.; Pandey, S.; Levy, D. et al. (2010). "Dietary factors and incident atrial fibrillation: The Framingham Heart Study". American Journal of Clinical Nutrition 93 (2): 261–6. doi:10.3945/ajcn.110.001305. PMC 3021424. PMID 21106919.
- Ramsden, C; Zamora, D; Leelarthaepin, B; Majchrzak-Hong, S; Faurot, K; Suchindran, C; Ringel, A; Davis, J; Hibbeln, J (February 2013). "Use of dietary linoleic acid for secondary prevention of coronary heart disease and death: evaluation of recovered data from the Sydney Diet Heart Study and updated meta-analysis". BMJ Group 346: e8707. doi:10.1136/bmj.e8707. PMID 23386268.
- Ozias, MK; Carlson, SE; Levant, B (2007). "Maternal Parity and Diet (n-3) Polyunsaturated Fatty Acid Concentration Influence Accretion of Brain Phospholipid Docosahexaenoic Acid in Developing Rats". The Journal of Nutrition 137 (1): 125sex–9. PMID 17182812.
- Patterson, R. E.; Flatt, S. W.; Newman, V. A.; Natarajan, L.; Rock, C. L.; Thomson, C. A.; Caan, B. J.; Parker, B. A.; Pierce, J. P. (2010). "Marine Fatty Acid Intake is Associated with Breast Cancer Prognosis". The Journal of Nutrition 141 (2): 201–206. doi:10.3945/jn.110.128777. PMC 3021439. PMID 21178081.
- "New findings measure precise impact of fat on cancer spread". 2009.
- Scislowski, Valérie; Bauchart, Dominique; Gruffat, Dominique; Laplaud, Paul-Michel; Durand, Denys (2005). "Effect of dietary n-6 and n-3 polyunsaturated fatty acids on peroxidizability of lipoproteins in steers". Lipids 40 (12): 1245–56. doi:10.1007/s11745-005-1492-z. PMID 16477809.
- Diniz, Yeda Sant'Ana; Cicogna, Antonio C; Padovani, Carlos R; Santana, Lea S; Faine, Luciane A; Novelli, Ethel L.B (2004). "Diets rich in saturated and polyunsaturated fatty acids: metabolic shifting and cardiac health". Nutrition 20 (2): 230–4. doi:10.1016/j.nut.2003.10.012. PMID 14962692.
- Quiles, José L; Ochoa, Julio J; Huertas, Jesús R; Mataix, José (2004). "Coenzyme Q supplementation protects from age-related DNA double-strand breaks and increases lifespan in rats fed on a PUFA-rich diet". Exp Gerontol. 39 (2): 189–94. doi:10.1016/j.exger.2003.10.002. PMID 15036411.
- Guyenet, Stephen. "does dietary saturated fat increase blood cholesterol?". Retrieved 13 November 2011.
- "National nutrient database for standard reference, release 23". United States Department of Agriculture, Agricultural Research Service. 2011.
- nutritiondata.com → Oil, vegetable, sunflower Retrieved on September 27, 2010
- USDA → Basic Report: 04042, Oil, peanut, salad or cooking Retrieved on January 16, 2015
- nutritiondata.com → Egg, yolk, raw, fresh Retrieved on August 24, 2009
- "09038, Avocados, raw, California". National Nutrient Database for Standard Reference, Release 26. United States Department of Agriculture, Agricultural Research Service. Retrieved 14 August 2014.
- "Feinberg School > Nutrition > Nutrition Fact Sheet: Lipids". Northwestern University. Archived from the original on 2011-07-20.