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In nutrition, polyunsaturated fat, or polyunsaturated fatty acid, are fatty acids in which more than one carbon-carbon double bond exists within the molecule. That is, the molecule has two or more points on its structure capable of bonding additional 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. One method for specifying Carbon atoms in a fatty acid is by using 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.

Benefits
Polyunsaturated fat can be found mostly in nuts, 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 (DHA), however, the most abundant n-3 PUFA [Omega-3] in erythrocyte 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.'''

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). Essential fatty acids (EFA) in polyunsaturated fats are shown to decrease the risk of depression, hypertension, and attention deficit hyperactivity disorder.

There exist 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.

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.'''

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. 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.

Food sources of polyunsaturated fat
10% of a person’s daily caloric intake should be consumed from polyunsaturated fats.