Essential fatty acid

Essential fatty acids, or EFAs, are fatty acids that cannot be constructed within an organism from other components (generally all references are to humans) by any known chemical pathways; and therefore mustbe obtained from the diet. The term refers to those involved in biological processes, and not fatty acids which may just play a role as fuel. As many of the compounds created from essential fatty acids can be taken directly in the diet, it is possible that the amounts required in the diet (if any) are overestimated. It is also possible they can be underestimated as organisms can still survive in nonideal, malnourished conditions.

There are two families of EFAs: ω-3 (or omega-3 or n−3) and ω-6 (omega-6, n−6). Fats from each of these families are essential, as the body can convert one omega-3 to another omega-3, for example, but cannot create an omega-3 from scratch.They were originally designated as Vitamin F when they were discovered as essential nutrients in 1923. In 1930, work by Burr, Burr and Miller showed that they are better classified with the fats than with the vitamins.cite journal
author=Burr, G.O., Burr, M.M. and Miller, E.|year=1930
url=http://www.jbc.org/cgi/reprint/97/1/1.pdf |accessdate=2007-01-17
title= On the nature and role of the fatty acids essential in nutrition
journal=J. Biol. Chem.| volume=86 |issue=587|format=PDF]

Functions

:"The biological effects of the ω-3 and ω-6 fatty acids are mediated by their mutual interactions, see Essential fatty acid interactions for detail."In the body, essential fatty acids serve multiple functions. In each of these, the balance between dietary ω-3 and ω-6 strongly affects function.
*They are modified to make
**the classic eicosanoids (affecting inflammation and many other cellular functions)
**the endocannabinoids (affecting mood, behavior and inflammation)
**the lipoxins from ω-6 EFAs and resolvins from ω-3 (in the presence of aspirin, downregulating inflammation.)
**the isofurans, neurofurans, isoprostanes, hepoxilins, epoxyeicosatrienoic acids (EETs) and Neuroprotectin D
*They form lipid rafts (affecting cellular signaling)cite journal | author=Stillwell W, Shaikh SR, Zerouga M, Siddiqui R, Wassall SR | title=Docosahexaenoic acid affects cell signaling by altering lipid rafts | journal=Reproduction, Nutrition, Development | volume=45 | issue=5 | year=2005 | pages=559–579 | pmid=16188208 | doi=10.1051/rnd:2005046]
*They act on DNA (activating or inhibiting transcription factors such as NFκB, which is linked to pro-inflammatory cytokine production)cite journal | author=Calder PC | title=n-3 fatty acids, inflammation, and immunity--relevance to postsurgical and critically ill patients | journal=LIPIDS | volume=39 | issue=12 | year=2004 | pages=1147–1161 | pmid=15736910 | doi=10.1007/s11745-004-1342-z]

Nomenclature and terminology

Fatty acids are straight chain hydrocarbons possessing a carboxyl (COOH) group at one end. The carbon next to the carboxylate is known as α, the next carbon β, and so forth. Since biological fatty acids can be of different lengths, the last position is labelled ω, the last letter in the Greek alphabet. Since the physiological properties of unsaturated fatty acids largely depend on the position of the first unsaturation relative to the end position and not the carboxylate, the position is signified by (ω minus n). For example, the term ω-3 signifies that the first double bond exists as the third carbon-carbon bond from the terminal CH₃ end (ω) of the carbon chain. The number of carbons and the number of double bonds is also listed. ω-3 18:4 (stearidonic acid) or 18:4 ω-3 or 18:4 n−3 indicates an 18-carbon chain with 4 double bonds, and with the first double bond in the third position from the CH₃ end. Double bonds are "cis" and separated by a single methylene (CH₂) group unless otherwise noted. So in free fatty acid form, the chemical structure of stearidonic acid is:

Examples

:"For complete tables of ω-3 and ω-6 essential fatty acids, see Polyunsaturated fatty acids.The essential fatty acids start with the short chain polyunsaturated fatty acids (SC-PUFA):
*ω-3 fatty acids:
**α-Linolenic acid or ALA (18:3)
*ω-6 fatty acids:
**Linoleic acid or LA (18:2)These two fatty acids cannot be synthesised by humans, as humans lack the desaturase enzymes required for their production.

They form the starting point for the creation of longer and more desaturated fatty acids, which are also referred to as long-chain polyunsaturated fatty acids (LC-PUFA):
*ω-3 fatty acids:
**eicosapentaenoic acid or EPA (20:5)
**docosahexaenoic acid or DHA (22:6)
*ω-6 fatty acids:
**gamma-linolenic acid or GLA (18:3)
**dihomo-gamma-linolenic acid or DGLA (20:3)
**arachidonic acid or AA (20:4)

ω-9 fatty acids are not essential in humans, because humans generally possess all the enzymes required for their synthesis. Exceptions do occur in older people or people with a liver problem that do not completely produce a sufficient amount,fact|date=January 2008 and hence many supplement companies market Omega 3-6-9 blends.

Essentiality

Between 1930 and 1950, arachidonic acid and linolenic acid were termed 'essential' because each was more or less able to meet the growth requirements of rats given fat-free diets. Further research has shown that human metabolism requires both ω-3 and ω-6 fatty acids. To some extent, any ω-3 and any ω-6 can relieve the worst symptoms of fatty acid deficiency. Particular fatty acids are still needed at critical life stages (e.g. lactation) and in some disease states. In nonscientific writing, common usage is that the term "essential fatty acid" comprises all the ω-3 or -6 fatty acids. [Or at least the polyunsaturated, straight-chain methylene-interrupted ones; conjugated fatty acids like calendic acid are not.] Authoritative sources include the whole families, without qualification.
*"Omega-3 fatty acids and their counterparts, n-6 fatty acids, are essential polyunsaturated fatty acids (PUFA) because they cannot be synthesized de novo in the body."] cite journal |author=Nugent K, Spigelman A, Phillips R |title=Tissue prostaglandin levels in familial adenomatous polyposis patients treated with sulindac |journal=Dis Colon Rectum |volume=39 |issue=6 |pages=659–62 |year=1996 |pmid=8646953 |doi=10.1007/BF02056946
*"Arachidonic acid is an essential fatty acid..."] cite journal |author=Carlstedt-Duke J, Brönnegård M, Strandvik B |title=Pathological regulation of arachidonic acid release in cystic fibrosis: the putative basic defect |journal=Proc Natl Acad Sci USA |volume=83 |issue=23 |pages=9202–6 |year=1986 |pmid=3097647 |doi=10.1073/pnas.83.23.9202
*" [T] he turnover of essential fatty acids is increased (7). Arachidonic acid is one of the essential fatty acids affected."] The human body can make some long-chain PUFA (arachidonic acid, EPA and DHA) from lineolate or lineolinate.

Traditionally speaking the LC-PUFA are not essential. See (Cunnane 2003)cite journal | author=Cunnane SC | title=Problems with essential fatty acids: time for a new paradigm? | journal=Progress in Lipid Research | volume=42 | issue=6 | year=2003 | pages=544–568 | pmid=14559071 | doi=10.1016/S0163-7827(03)00038-9] for a discussion of the current status of the term 'essential'. Because the LC-PUFA are sometimes required, they may be considered "conditionally essential", or not essential to healthy adults.

Mary G. Enig has pointed out numerous studies showing the need for omega-3 and omega-6 essential fatty acids in mammaliansCitation|last = Enig |first = M | title = Know Your Fats: The Complete Primer for Understanding the Nutrition of Fats, Oils and Cholesterol |place= Silver Spring, MD| publisher = Bethesda Press| year = 2001| edition = First Edition | isbn = 0-9678126-0-7*] A 2005 study has shown evidence that gamma-linolenic acid, GLA, a product of omega-6, has been shown to inhibit the breast cancer promoting gene of Her2/neu. cite journal|author = Menendez JA, Vellon R, Colomer R, Lupu R |title = Effect of gamma-linolenic acid on the transcriptional activity or Her2/neu (Erb-2) oncogene |journal = J Natl Cancer Inst |volume = 97 |issue = 2 |pages = 1611–1615 |year = 2005 |pmid = 16264182*]

Biologist Ray Peat has pointed out flaws in the studies purportedly showing the need for n-3 and n-6 fats. He notes that so-called EFA deficiencies have sometimes been reversed by adding B vitamins or a fat-free liver extract to the diet. In his view, 'the optional dietary level of the "essential fatty acids" might be close to zero, if other dietary factors were also optimized.' [http://raypeat.com/articles/nutrition/oils-in-context.shtml]

Essential fatty acids should not be confused with essential oils, which are "essential" in the sense of being a concentrated essence.

Food sources

Almost all the polyunsaturated fat in the human diet is from EFA. Some of the food sources of ω-3 and ω-6 fatty acids are fish and shellfish, flaxseed (linseed), hemp oil, soya oil, canola (rapeseed) oil, chia seeds, pumpkin seeds, sunflower seeds, leafy vegetables, and walnuts.

Essential fatty acids play a part in many metabolic processes, and there is evidence to suggest that low levels of essential fatty acids, or the wrong balance of types among the essential fatty acids, may be a factor in a number of illnesses, including osteoporosis. [cite journal| title=Calcium metabolism, osteoporosis and essential fatty acids: a review | pmid= 9624425 | accessdate=2008-02-26]

Plant sources of ω-3 contain neither eicosapentaenoic acid (EPA) nor docosahexaenoic acid (DHA). The human body can (and in case of a purely vegetarian diet often must, unless certain algae or supplements derived from them are consumed) convert α-linolenic acid (ALA) to EPA and subsequently DHA. This however requires more metabolic work, which is thought to be the reason that the absorption of essential fatty acids is much greater from animal rather than plant sources (see Fish and plants as a source of Omega-3 for more).

The PDFlink| [http://www.iupac.org/publications/pac/2001/pdf/7304x0685.pdf IUPAC Lipid Handbook] |370 KiB provides a very large and detailed listing of fat contents of animal and vegetable fats, including ω-3 and -6 oils. The National Institutes of Health's EFA Education group publishes [http://efaeducation.nih.gov/sig/esstable1.html 'Essential Fats in Food Oils.'] This lists 40 common oils, more tightly focused on EFAs and sorted by n-6:3 ratio. PDFlink| [http://publib.upol.cz/~obd/fulltext/Biomedic146-2/LF11_2002-1.pdf Stuchlik and Zak, 'Vegetable Lipids as Components of Functional Food'] |139 KiB list notable vegetable sources of EFAs as well as commentary and an overview of the biosynthetic pathways involved. Users can interactively search at [http://www.nutritiondata.com/index.html Nutrition Data] for the richest food sources of particular EFAs or other nutrients. Careful readers will note that these sources are not in excellent agreement. EFA content of vegetable sources varies with cultivation conditions. Animal sources vary widely, both with the animal's feed and that the EFA makeup varies markedly with fats from different body parts.

Human health

Almost all the polyunsaturated fats in the human diet are EFAs. Essential fatty acids play an important role in the life and death of cardiac cells. [cite journal| title=External blockade...by polyunsaturated fatty acids | pmid = 43279| accessdate=2007-01-18 - see page 1 of this link] [cite journal| title=Antiarrhythmic effects of omega-3 fatty acids | pmid=16919517 | accessdate=2007-01-18] [cite journal| title=Alpha-linolenic acid, cardiovascular disease and sudden death | pmid= 17086218 | accessdate=2007-01-18] [cite journal| title=Omega-3 and health | pmid= 17091903| accessdate=2007-01-18]

ee also

*Polyunsaturated fat
*Omega-3 fatty acid
*Omega-6 fatty acid
*Essential fatty acid interactions
*Eicosanoid
**Prostaglandin
**Leukotriene
**Thromboxane
*Nonclassic eicosanoid
*Endogenous Cannabinoid
*Essential nutrient
*Essential amino acid
*Fatty acid metabolism
*Fatty acid synthase
*Oily fish

References

External links

* [http://www.benbest.com/health/essfat.html Fats You Need -- Essential Fatty Acids]
* [http://www.nal.usda.gov/fnic/foodcomp/Bulletins/faq.html#omega USDA] (public domain resource, and a source for this article)
*Cite web|author=Cunnane Stephen C|title=Essential Fatty Acids: Time for a New Paradigm?|work=PUFA Newsletter|month=June | year=2005|accessdate=2006-03-14|url=http://www.fatsoflife.com/pufa/article.asp?nid=1&edition=arch&id=266
*cite web| url=http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=pubmed&dopt=Abstract&list_uids=14580707&query_hl=55 | title=Docosahexaenoic acid: membrane properties of a unique fatty acid.|author=Stillwell W, Wassall SR. |publishdate= November 2003 |accessmonthday=February 8 |accessyear= 2006 Chem Phys Lipids. 2003 Nov;126(1):1-27