Polyunsaturated fat
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In nutrition, polyunsaturated fat, or polyunsaturated fatty acid, are fatty acids in which more than one double bond exists within the representative molecule. That is, the molecule has two or more points on its structure capable of supporting hydrogen atoms not currently part of the structure. Polyunsaturated fatty acids can assume a cis or trans conformation depending on the geometry of the double bond.
The lack of the extra hydrogen atoms on the molecule's surface typically reduces the strength of the compound's intermolecular forces, thus causing the melting point of the compound to be significantly lower. This property can be observed by comparing predominately unsaturated vegetable oils, which remain liquid even at relatively low temperatures, to much more saturated fats such as butter or lard which are mainly solid at room temperature. Trans fats are more similar to saturated fat than are cis fats in many respects, including the fact that they solidify at a higher temperature than cis fats.
A fatty acid has a carboxylic acid at one end and a methyl group at the other end. Carbon atoms in a fatty acid are identified by Greek letters on the basis of their distance from the carboxylic acid. The carbon atom closest to the carboxylic acid is the alpha carbon, the next adjacent carbon is the beta carbon, etc. In a long-chain fatty acid the carbon atom in the methyl group 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.
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Health
Benefits
Polyunsaturated fat can be found mostly in nuts, cheese, seeds, fish, algae, leafy greens, and krill. Whole food sources are always best, as processing and heating may damage polyunsaturated fats. Omega-3 fatty acids in fish oil, fish and seafood have been shown to lower the risk of heart attacks. Omega-6 fatty acids in sunflower oil and safflower oil may also reduce the risk of cardiovascular disease. Consumption of refined sugar and refined grain products also cause the body to metabolize omega-6 fats into pro-inflammatory prostaglandins.
Omega-3 fatty acids reduced prostate tumor growth, slowed histopathological progression, and increased survival. 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, however, the most abundant n-3 PUFA [Omega-3] in erythrocyte membranes, were associated with a reduced risk of breast cancer.
Dietary intake of polyunsaturated fatty acids has been shown in several studies to decrease the risk of developing amyotrophic lateral sclerosis (ALS, a.k.a. Lou Gehrig's Disease).
Relation to cancer
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. [1]. 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,[1] [2] . 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. However, studies in humans have found little evidence of an association between polyunsaturated fat and the risk of cancer. 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 more beneficial than harmful in terms of its effect on reducing cholesterol levels.
A high consumption of omega-6 polyunsaturated fatty acids (PUFAs), which are found in most types of vegetable oil, may increase the likelihood that postmenopausal women will develop breast cancer. Similar effect was observed on prostate cancer. Other analysis suggested an inverse association between total polyunsaturated fatty acids and breast cancer risk, but individual polyunsaturated fatty acids behaved differently from each other.
Some examples of foods containing polyunsaturated fat
- fish (wild salmon - 2.5 grams per 100 grams)
- whole grain wheat (0.8 grams per 100 grams)
- peanut butter (14.2 grams per 100 grams)
- margarine (around 24 grams per 100 grams, but may also contain some trans fat)
- bananas (however, at .33 grams fat per serving, this food is considered "fat-free" by FDA standards)
- sunflower seeds
- hemp seed
See also
- Monounsaturated fat
- For listings of particular classes, see
- Essential fatty acid - for biochemistry of most polyunsaturated fats
- Essential fatty acid interactions - for the interactions between ω-6 and ω-3 fatty acids
- Unsaturated fat
References
- ^ National Institute of Health (August 1, 2005). "Omega-3 fatty acids, fish oil, alpha-linolenic acid". http://www.nlm.nih.gov/medlineplus/print/druginfo/natural/patient-fishoil.html. Retrieved 26 March 2006.
- ^ Willett WC (September 2007). "The role of dietary n-6 fatty acids in the prevention of cardiovascular disease". Journal of Cardiovascular Medicine 8 Suppl 1: S42–5. doi:10.2459/01.JCM.0000289275.72556.13 (inactive 2010-03-20). PMID 17876199.
- ^ Mihelin M, Trontelj JV, Stålberg E (August 1991). "Muscle fiber recovery functions studied with double pulse stimulation". Muscle & Nerve 14 (8): 739–47. doi:10.1002/mus.880140808. PMID 1890998.
- ^ a b Pala V, Krogh V, Muti P, et al. (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.
- ^ Veldink JH, Kalmijn S, Groeneveld GJ, et al. (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. PMID 16648143.
- ^ Okamoto K, Kihira T, Kondo T, 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.
- ^ Scislowski V, Bauchart D, Gruffat D, Laplaud PM, Durand D (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 YS, Cicogna AC, Padovani CR, Santana LS, Faine LA, Novelli EL (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 JL, Ochoa JJ, Huertas JR, Mataix J (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.
- ^ Whitney D, Cavanagh P (August 2000). "The position of moving objects". Science 289 (5482): 1107. doi:10.1126/science.289.5482.1107a. PMID 10970215.
- ^ Mihelin M, Trontelj JV, Stålberg E (August 1991). "Muscle fiber recovery functions studied with double pulse stimulation". Muscle & Nerve 14 (8): 739–47. doi:10.1002/mus.880140808. PMID 1890998.
- ^ http://www.nal.usda.gov/fnic/foodcomp/search/
- ^ a b c .nutritiondata.com --> Egg, yolk, raw, fresh Retrieved on August 24, 2009
- ^ Feinberg School > Nutrition > Nutrition Fact Sheet: Lipids Northwestern University. Retrieved on August 24, 2009
External links
- The Chemistry of Unsaturated Fats
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