Inbiochemistry and nutrition, apolyunsaturated fat is afat that contains apolyunsaturated fatty acid (abbreviatedPUFA), which is a subclass offatty acid characterized by a backbone with two or more carbon–carbondouble bonds.^[1][2]Some polyunsaturated fatty acids areessentials. Polyunsaturated fatty acids are precursors to and are derived from polyunsaturatedfats, which includedrying oils.^[3]

The position of the carbon-carbon double bonds incarboxylic acid chains in fats is designated byGreek letters.^[1] The carbon atom closest to thecarboxyl group is thealpha carbon, the next carbon is thebeta carbon andso on. In fatty acids the carbon atom of themethyl group at the end of the hydrocarbon chain is called theomega carbon becauseomega is the last letter of the Greek alphabet.Omega-3 fatty acids have a double bond three carbons away from the methyl carbon, whereasomega-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.

Polyunsaturated fatty acids can be classified in various groups by their chemical structure:

• methylene-interrupted polyenes
• conjugated fatty acids
• other PUFAs

Based on the length of their carbon backbone, they are sometimes classified in two groups:^[4] All featurepentadiene groups.

• short chain polyunsaturated fatty acids (SC-PUFA), with 18 carbon atoms. These are more common. Key members includelinoleic acid, α-linolenic acid, andarachidonic acid.^[5]
• long-chain polyunsaturated fatty acids (LC-PUFA) with 20 or more carbon atoms

PUFAs with 18 carbon atoms, which are the most common variety, are not produced by mammals. Since they have important dietary functions, theirbiosynthesis has received much attention. Plants produce PUFAs fromoleic acid. Key enzymes are calledfatty acid desaturases, which introduce additional double bonds. Desaturases convert oleic acid intolinoleic acid the precursor toalpha-linolenic acid,gamma-linolenic acid anddihomo-gamma-linolenic acid.^[6]

Industrial PUFAs are generally obtained by hydrolysis of fats that contain PUFAs. The process is complicated by the sensitive nature of PUFAs, leading to side reactions and colorization. Thus, steam hydrolysis often fails for this reason. Alkaline hydrolysis of fats followed by acidification is expensive.Lipases, a family of enzymes, show potential as mild andgreen catalysts for the production of PUFAs from triglycerides.^[3]

In general, outside of dietary contexts, PUFAs are undesirable components of vegetable oils, so there is great interest in their removal from, say, olive oil. One technology for lowering the PUFA contact is by selective formation of derivatives withureas.^[3]

From the perspective of chemicalanalysis, PUFA's have highiodine numbers. These high values are simply a reflection of the fact that PUFAs arepolyunsaturated. Hydrogenation of PUFAs gives less unsaturated derivatives. For unsaturated products from partial hydrogenation often contain some trans isomers. The transmonounsaturated C20 specieselaidic acid can be prepared in this way.^[3]

Polyunsaturated fatty acids are susceptible tolipid peroxidation, far more so than monounsaturated or saturated analogues. The basis for this reactivity is the weakness of doublyallylic C-H bonds. They aredrying oils, i.e. film-forming liquids suitable as painting. One practical consequence is that polyunsaturated fatty acids have poor shelf life, owing to their tendency towardautoxidation, leading, in the case of edibles, torancidification. Metals accelerate the degradation. A range of reactions with oxygen occur. Products include fatty acidhydroperoxides, epoxy-hydroxy polyunsaturated fatty acids,jasmonates,divinylether fatty acids, andleaf aldehydes. Some of these derivatives are signalling molecules, some are used in plant defense (antifeedants), some are precursors to other metabolites that are used by the plant.^[5]

These fatty acids have 2 or morecis double bonds that are separated from each other by a singlemethylene bridge (-CH
₂-). This form is also sometimes called adivinylmethane pattern.^[7]

The essential fatty acids are all omega-3 and -6 methylene-interrupted fatty acids.See more atEssential fatty acids—Nomenclature^[8]

The biological effects of the ω-3 and ω-6 fatty acids are largely mediated by their mutual interactions, seeEssential fatty acid interactions for detail.

Because of their effects in the diet, unsaturated fats (monounsaturated and polyunsaturated) are often referred to asgood fats; while saturated fats are sometimes referred to asbad fats. Some fat is needed in the diet, but it is usually considered that fats should not be consumed excessively, unsaturated fats should be preferred, and saturated fats in particular should be limited.^{[9][10][11][12]}

In preliminary research,omega-3 fatty acids in algal oil, fish oil, fish and seafood have been shown to lower the risk ofheart attacks.^[13] Other preliminary research indicates thatomega-6 fatty acids insunflower oil andsafflower oil may also reduce the risk of cardiovascular disease.^[14]

Among omega-3 fatty acids, neither long-chain nor short-chain forms were consistently associated with breast cancer risk. High levels ofdocosahexaenoic acid (DHA), however, the most abundant omega-3 polyunsaturated fatty acid in erythrocyte (red blood cell) membranes, were associated with a reduced risk of breast cancer.^[15]DHA is vital for thegrey matter structure of the human brain, as well as retinal stimulation andneurotransmission.^[1]

Contrary to conventional advice, an evaluation of evidence from 1966–1973 pertaining to the health impacts of replacing dietarysaturated fat withlinoleic acid found that participants in the group doing so hadincreased rates of death from all causes, coronary heart disease, and cardiovascular disease.^[16] Although this evaluation was disputed by many scientists,^[17] it fueled debate over worldwide dietary advice to substitute polyunsaturated fats for saturated fats.^[18]

Takingisotope-reinforced polyunsaturated fatty acids, for exampledeuterated linoleic acid where two atoms of hydrogen substituted with its heavy isotope deuterium, with food (heavy isotope diet) can suppress lipid peroxidation and prevent or treat the associated diseases.^[19][20]

Polyunsaturated fat supplementation does not decrease the incidence of pregnancy-related disorders, such ashypertension orpreeclampsia, but may increase the length ofgestation slightly and decreased the incidence of early premature births.^[1]

Expert panels in the United States and Europe recommend that pregnant and lactating women consume higher amounts of polyunsaturated fats than the general population to enhance the DHA status of the fetus and newborn.^[1]

Results fromobservational clinical trials on polyunsaturated fat intake and cancer have been inconsistent and vary by numerous factors of cancer incidence, including gender and genetic risk.^[13] Some studies have shown associations between higher intakes and/or blood levels of polyunsaturated fat omega-3s and a decreased risk of certain cancers, includingbreast andcolorectal cancer, while other studies found no associations with cancer risk.^[13][21]

Polyunsaturated fat can be found mostly in nuts, seeds, fish, seed oils, andoysters.^[1] "Unsaturated" refers to the fact that the molecules contain less than the maximum amount of hydrogen (if there were no double bonds). These materials exist ascis ortransisomers depending on the geometry of the double bond.

PUFA's are significant components ofalkyd resins, which are used incoatings.^[3]

• Cyberlipid."Polyenoic Fatty Acids". Archived fromthe original on 2018-09-30. Retrieved2007-01-17.
• Gunstone, Frank D."Lipid Glossary 2"(PDF). Archived fromthe original(PDF) on 2006-08-13. Retrieved2007-01-17.
• Adlof, R. O. & Gunstone, F. D. (2003-09-17)."Common (non-systematic) Names for Fatty Acids". Archived fromthe original on 2006-12-06. Retrieved2007-01-24.
• Heinz; Roughan, PG (1983)."Similarities and Differences in Lipid Metabolism of Chloroplasts Isolated from 18:3 and 16:3 Plants".Plant Physiol.72 (2):273–279.doi:10.1104/pp.72.2.273.PMC 1066223.PMID 16662992.

• Fatty acids
• Nutrition
• Nutrients

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