“Polyunsaturated fat”的意思、由来-开放百科全书

Polyunsaturated fats are fats in which the constituent hydrocarbon chain possesses two or more carbon–carbon double bonds.^[1]^[2] Polyunsaturated fat can be found mostly in nuts, seeds, fish, seed oils, and oysters.^[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 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. In general, this means that the melting points of fats increase from cis to trans unsaturated and then to saturated. See the section about the 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.^[1] 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 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.

Health

Potential benefits

Because of their effects in the diet, unsaturated fats (monounsaturated and polyunsaturated) are often referred to as good fats; while saturated fats are sometimes referred to as bad 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.^[3]^[4]^[5]^[6]

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.^[7] Other preliminary research indicates that omega-6 fatty acids in sunflower oil and safflower oil may also reduce the risk of cardiovascular disease.^[8]

Among omega-3 fatty acids, neither long-chain nor short-chain forms were consistently associated with breast cancer risk. High levels of docosahexaenoic 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.^[9] The DHA obtained through the consumption of polyunsaturated fatty acids is positively associated with cognitive and behavioral performance.^[10] In addition DHA is vital for the grey matter structure of the human brain, as well as retinal stimulation and neurotransmission.^[1]

Contrary to conventional advice, an evaluation of evidence from 1966-1973 pertaining to the health impacts of replacing dietary saturated fat with linoleic acid found that participants in the group doing so had increased rates of death from all causes, coronary heart disease, and cardiovascular disease.^[11] Although this evaluation was disputed by many scientists,^[12] it fueled debate over worldwide dietary advice to substitute polyunsaturated fats for saturated fats.^[13]

Pregnancy

Polyunsaturated fat supplementation does not decrease the incidence of pregnancy-related disorders, such as hypertension or preeclampsia, but may increase the length of gestation 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]

Cancer

Results from observational clinical trials on polyunsaturated fat intake and cancer have been inconsistent and vary by numerous factors of cancer incidence, including gender and genetic risk.^[7] Some studies have shown associations between higher intakes and/or blood levels of polyunsaturated fat omega-3s and a decreased risk of certain cancers, including breast and colorectal cancer, while other studies found no associations with cancer risk.^[7]^[14]

Food sources

References

1. ^¹²³⁴⁵⁶{{cite web|title=Essential Fatty Acids|url=http://lpi.oregonstate.edu/mic/other-nutrients/essential-fatty-acids|publisher=Micronutrient Information Center, Oregon State University, Corvallis, OR|access-date=24 May 2017|date=May 2014}}
2. ^{{cite web|title=Omega-3 fatty acids, fish oil, alpha-linolenic acid|url=http://www.mayoclinic.com/health/fish-oil/NS_patient-fishoil/|publisher=Mayo Clinic|date=2017|access-date=24 May 2017}}
3. ^{{cite web |title=Fats explained |url=https://www.heartuk.org.uk/downloads/factsheets/fats-explained.pdf |website=HEART UK – The Cholesterol Charity |accessdate=20 February 2019}}
4. ^{{cite web |title=Key Recommendations: Components of Healthy Eating Patterns |url=https://health.gov/dietaryguidelines/2015/guidelines/chapter-1/key-recommendations/ |website=Dietary Guidelines 2015-2020 |accessdate=20 February 2019}}
5. ^{{cite web |title=Live Well, Eat well, Fat: the facts |url=https://www.nhs.uk/live-well/eat-well/different-fats-nutrition/ |website=NHS |accessdate=20 February 2019}}
6. ^{{cite web |title=Dietary Guidelines for Indians - A Manual |url=http://ninindia.org/DietaryGuidelinesforNINwebsite.pdf |website=Indian Council of Medical Research, National Institute of Nutrition}}
7. ^¹²{{cite web|url=http://ods.od.nih.gov/factsheets/Omega3FattyAcids-HealthProfessional/|publisher=US National Institutes of Health, Office of Dietary Supplements|title=Omega-3 Fatty Acids and Health: Fact Sheet for Health Professionals|date=2 November 2016|access-date=5 April 2017}}
8. ^{{cite journal | vauthors = Willett WC | title = The role of dietary n-6 fatty acids in the prevention of cardiovascular disease | journal = Journal of Cardiovascular Medicine | volume = 8 Suppl 1 | issue = | pages = S42-5 | date = September 2007 | pmid = 17876199 | doi = 10.2459/01.JCM.0000289275.72556.13 }}
9. ^{{cite journal | vauthors = Pala V, Krogh V, Muti P, Chajès V, Riboli E, Micheli A, Saadatian M, Sieri S, Berrino F | title = Erythrocyte membrane fatty acids and subsequent breast cancer: a prospective Italian study | journal = Journal of the National Cancer Institute | volume = 93 | issue = 14 | pages = 1088–95 | date = July 2001 | pmid = 11459870 | doi = 10.1093/jnci/93.14.1088 }}
10. ^{{cite journal | vauthors = van de Rest O, Geleijnse JM, Kok FJ, van Staveren WA, Dullemeijer C, Olderikkert MG, Beekman AT, de Groot CP | title = Effect of fish oil on cognitive performance in older subjects: a randomized, controlled trial | journal = Neurology | volume = 71 | issue = 6 | pages = 430–8 | date = August 2008 | pmid = 18678826 | doi = 10.1212/01.wnl.0000324268.45138.86 }}
11. ^{{cite journal | vauthors = Ramsden CE, Zamora D, Leelarthaepin B, Majchrzak-Hong SF, Faurot KR, Suchindran CM, Ringel A, Davis JM, Hibbeln JR | title = 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 | journal = BMJ | volume = 346 | pages = e8707 | date = February 2013 | pmid = 23386268 | pmc = 4688426 | doi = 10.1136/bmj.e8707 }}
12. ^{{cite web|url=https://www.hsph.harvard.edu/nutritionsource/2016/04/13/diet-heart-ramsden-mce-bmj-comments/|title=Research Review: Old data on dietary fats in context with current recommendations: Comments on Ramsden et al. in the British Medical Journal|author=Interview: Walter Willett|publisher=TH Chan School of Public Health, Harvard University, Boston|date=2017|access-date=24 May 2017}}
13. ^{{cite journal | vauthors = Weylandt KH, Serini S, Chen YQ, Su HM, Lim K, Cittadini A, Calviello G | title = Omega-3 Polyunsaturated Fatty Acids: The Way Forward in Times of Mixed Evidence | journal = BioMed Research International | volume = 2015 | pages = 143109 | year = 2015 | pmid = 26301240 | pmc = 4537707 | doi = 10.1155/2015/143109 }}
14. ^{{cite journal | vauthors = Patterson RE, Flatt SW, Newman VA, Natarajan L, Rock CL, Thomson CA, Caan BJ, Parker BA, Pierce JP | title = Marine fatty acid intake is associated with breast cancer prognosis | journal = The Journal of Nutrition | volume = 141 | issue = 2 | pages = 201–6 | date = February 2011 | pmid = 21178081 | pmc = 3021439 | doi = 10.3945/jn.110.128777 }}
15. ^{{cite web|publisher=United States Department of Agriculture, Agricultural Research Service|year=2011|title= National nutrient database for standard reference, release 23 |url=http://www.nal.usda.gov/fnic/foodcomp/search/}}
16. ^{{cite web|url=http://nutritiondata.self.com/facts/fats-and-oils/620/2|title=Vegetable oil, avocado Nutrition Facts & Calories |website=nutritiondata.self.com}}
17. ^{{Cite web|url = http://ndb.nal.usda.gov/ndb/foods/show/658?manu=&fgcd=|title = United States Department of Agriculture – National Nutrient Database|date = 8 September 2015 }}