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.

Chemical structure of the polyunsaturated fat linoleic acid.

3D representation of linoleic acid in a bent conformation.

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.

[edit] Health

[edit] Benefits

Polyunsaturated fat can be found mostly in grain products, fish and sea food (herring, salmon, mackerel, halibut), soybeans, and fish oil. Foods like mayonnaise and soft margarine may also be good sources, but nutritional facts can vary by style and brand. Omega-3 fatty acids in fish oil, fish and seafood have been shown to lower the risk of heart attacks.^[1] Omega-6 fatty acids in sunflower oil and safflower oil may also reduce the risk of cardiovascular disease, but can contribute to allergies and inflammation.^{[citation needed]}

Omega-3 fatty acids reduced prostate tumor growth, slowed histopathological progression, and increased survival^[2]. 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.^[3].

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)^[4][5].

[edit] 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] ^{[6] [7]}. 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^[8]. 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.^{[citation needed]} 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^[9]. Similar effect was observed on prostate cancer^[2]. Other analysis suggested an inverse association between total polyunsaturated fatty acids and breast cancer risk, but individual polyunsaturated fatty acids behaved differently^[3] from each other.

[edit] Some Examples of Foods containing polyunsaturated fat

• fish (wild salmon - 2.5 grams per 100 grams)^[10]
• cereal
• 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 also high in trans fat)
• bananas (however, at .33 grams fat per serving, this food is considered "fat-free" by FDA standards)
• sunflower seeds
• hemp seed

Fat composition in different foods (click at right to hide or show)

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Food	Saturated	Monounsaturated	Polyunsaturated
	As weight percent (%) of total fat
Cooking oils
Canola oil	7	59	29
Corn oil	13	24	59
Olive oil	13	74	8
Soybean oil	15	24	58
Dairy Products
Cheese,regular	64	29	3
Cheese,light	60	30	0
Milk, whole	62	28	4
Milk, 2%	62	30	0
Ice cream, gourmet	62	29	4
Ice cream, light	62	29	4
Meats
Beef	33	38	5
Ground sirloin	38	44	4
Pork chop	35	44	8
Ham	35	49	16
Chicken breast	29	34	21
Chicken	34	23	30
Turkey breast	30	20	30
Turkey drumstick	32	22	30
Fish,orange roughy	23	15	46
Salmon	28	33	28
Hot dog, beef	42	48	5
Hot dog, turkey	28	40	22
Burger, fast food	36	44	6
Cheeseburger, fast food	43	40	7
Breaded chicken sandwich	20	39	32
Grilled chicken sandwich	26	42	20
Sausage, Polish	37	46	11
Sausage, turkey	28	40	22
Pizza, sausage	41	32	20
Pizza, cheese	60	28	5
Nuts
Almonds dry roasted	9	65	1
Cashews dry roasted	20	59	17
Macadamia dry roasted	15	79	2
Peanuts dry roasted	14	50	31
Pecans dry roasted	8	62	25
Flaxseeds, ground	8	23	65
Sesame seeds	14	38	44
Soybeans	14	22	57
Sunflower seeds	11	19	66
Walnuts dry roasted	9	23	63
Sweets and baked goods
Candy, chocolate bar	59	33	3
Candy, fruit chews	14	44	38
Cookie, oatmeal raisin	22	47	27
Cookie, chocolate chip	35	42	18
Cake, yellow	60	25	10
Pastry, Danish	50	31	14
Fats added during cooking or at the table
Butter, stick	63	29	3
Butter, whipped	62	29	4
Margarine, stick	18	39	39
Margarine, tub	16	33	49
Margarine, light tub	19	46	33
Lard	39	45	11
Shortening	25	45	26
Chicken fat	30	45	21
Beef fat	41	43	3
Dressing, blue cheese	16	54	25
Dressing, light Italian	14	24	58
Other
Egg yolk fat	36[11]	44[11]	16[11]
Unless else specified in boxes, then reference is: [12]

[edit] See also

• Monounsaturated fat
• For listings of particular classes, see
  • Polyunsaturated fatty acid
  • Omega-3 fatty acid
  • Omega-6 fatty acid
  • Omega-9 fatty acid
  • Conjugated linoleic acid
• 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

[edit] References

1. ^ 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. 
2. ^ ^{a b} Yong Q. Chen, at al (2007). "Modulation of prostate cancer genetic risk by omega-3 and omega-6 fatty acids". The Journal of Clinical Investigation 117 (7): 1866. doi:10.1172/JCI31494. PMID 1890998. http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=1890998. Retrieved 2008-11-30. 
3. ^ ^{a b} Valeria Pala, Vittorio Krogh, Paola Muti, Véronique Chajès, Elio Riboli, Andrea Micheli, Mitra Saadatian, Sabina Sieri, Franco Berrino (18 July 2001). "Erythrocyte Membrane Fatty Acids and Subsequent Breast Cancer: a Prospective Italian Study". JNCL 93 (14): 1088. doi:10.1093/jnci/93.14.1088. PMID 11459870. http://jnci.oxfordjournals.org/cgi/content/full/93/14/1088. Retrieved 2008-11-30. 
4. ^ Veldink JH, Kalmijn S, Groeneveld GJ, Wunderink W, Koster A, de Vries JH, van der Luyt J, Wokke JH, Van den Berg LH (April 2007). "Intake of polyunsaturated fatty acids and vitamin E reduces the risk of developing amyotrophic lateral sclerosis". J. Neurol. Neurosurg. Psychiatr. 78 (4): 367–71. doi:10.1136/jnnp.2005.083378. PMID 16648143. http://jnnp.bmj.com/cgi/pmidlookup?view=long&pmid=16648143. Retrieved 2009-03-13. 
5. ^ Okamoto K, Kihira T, Kondo T, Kobashi G, Washio M, Sasaki S, Yokoyama T, Miyake Y, Sakamoto N, Inaba Y, Nagai M (October 2007). "Nutritional status and risk of amyotrophic lateral sclerosis in Japan". Amyotroph Lateral Scler 8 (5): 300–4. doi:10.1080/17482960701472249. PMID 17852010. http://www.informaworld.com/openurl?genre=article&doi=10.1080/17482960701472249&magic=pubmed||1B69BA326FFE69C3F0A8F227DF8201D0. Retrieved 2009-03-13. 
6. ^ 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. 
7. ^ 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. 
8. ^ 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. 
9. ^ Emily Sonestedt, Ulrika Ericson, Bo Gullberg, Kerstin Skog, Håkan Olsson, Elisabet Wirfält (2008). "Do both heterocyclic amines and omega-6 polyunsaturated fatty acids contribute to the incidence of breast cancer in postmenopausal women of the Malmö diet and cancer cohort?". The International Journal of Cancer (UICC International Union Against Cancer) 123 (7): 1637–1643. doi:10.1002/ijc.23394. PMID 10970215. http://www3.interscience.wiley.com/journal/120780752/abstract. Retrieved 2008-11-30. 
10. ^ http://www.nal.usda.gov/fnic/foodcomp/search/
11. ^ ^{a b c} .nutritiondata.com --> Egg, yolk, raw, fresh Retrieved on August 24, 2009
12. ^ Feinberg School > Nutrition > Nutrition Fact Sheet: Lipids Northwestern University. Retrieved on August 24, 2009

[edit] External links

• The Chemistry of Unsaturated Fats