Essential fatty acid
Encyclopedia
Essential fatty acids, or EFAs, are fatty acid
s that humans and other animals must ingest because the body requires them for good health but cannot synthesize
them. The term "essential fatty acid" refers to fatty acids required for biological processes, and not those that only act as fuel.
Only two EFAs are known for humans: alpha-linolenic acid
(an omega-3 fatty acid
) and linoleic acid
(an omega-6 fatty acid
). Other fatty acids that are only "conditionally essential" include gamma-linolenic acid
(an omega-6 fatty acid), lauric acid
(a saturated fatty acid), and palmitoleic acid
(a monounsaturated fatty acid).
When the two EFAs were first discovered in 1923, they were designated Vitamin F. In 1930, work by Burr, Burr and Miller on rats showed that the two EFAs are better classified with the fat
s than with the vitamin
s.
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.
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 as a "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:
The essential fatty acids start with the short chain polyunsaturated fatty acids (SC-PUFA):
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-9 fatty acids
are not essential in humans, because humans generally possess all the enzymes required for their synthesis.
(18:3,9,12,15), abbreviated ALA, are essential for humans in the diet. In humans, arachidonic acid (20:4,5,8,11,14) can be synthesized from LA by desaturation and chain elongation (though some carnivores like cats cannot do this, and require arachadonate in the diet). In addition, the human body can make some long-chain ω-3 PUFAs (EPA and DHA) from the ω-3 ALA.
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 for its class. 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. Conjugated
fatty acids like calendic acid
are not normally considered essential. Authoritative sources include the whole families, without qualification.
Traditionally speaking the LC-PUFA are not essential. See (Cunnane 2003) 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.
A 2005 study has shown evidence that the ω-6 fat gamma-linolenic acid, GLA
has been shown to inhibit the breast cancer promoting gene of Her2/neu
.
Essential fatty acids should not be confused with essential oil
s, which are "essential" in the sense of being a concentrated essence.
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 walnut
s.
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
.
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 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 'Essential Fats in Food Oils.' This lists 40 common oils, more tightly focused on EFAs and sorted by n-6:3 ratio. list notable vegetable sources of EFAs as well as commentary and an overview of the biosynthetic pathways involved. Users can interactively search at 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.
s in the human diet are EFAs.
Essential fatty acids play an important role in the life and death of cardiac cells.
similar to that seen in zinc
or biotin deficiency
.
(DHA) and eicosapentaenoic acid
(EPA) are important for enzymatic pathways required to metabolize long-chain polyunsaturated fatty acids (PUFAs). Low plasma concentrations of DHA predict low concentrations of cerebrospinal fluid 5-hydroxyindoleacetic acid
(5-HIAA). It is found that low concentrations of 5-HIAA in the brain is associated with depression and suicide.
There are high concentrations of DHA in synaptic membranes of the brain. This is critical for synaptic transmission and membrane fluidity
. The omega-6 fatty acid
to omega-3 fatty acid
ratio is important to avoid imbalance of membrane fluidity. Membrane fluidity affects function of enzymes such as adenylate cyclase
and ion channels such as calcium
, potassium
, and sodium
, which in turn affects receptor numbers and functioning, as well as serotonin
neurotransmitter levels. It is evident that western diets are deficient in omega-3 and excessive in omega-6, and balancing of this ratio would confer numerous health benefits.
Clinical research suggests a benefit of omega-3 fatty acids in the treatment of depression during the perinatal period. A meta analysis of trials of EPA supplements for depression in non-pregnant adults concluded that supplments with more than 60% EPA are effective, but those containing primarily DHA, or less than 60% EPA, were not effective.
Fatty acid
In chemistry, especially biochemistry, a fatty acid is a carboxylic acid with a long unbranched aliphatic tail , which is either saturated or unsaturated. Most naturally occurring fatty acids have a chain of an even number of carbon atoms, from 4 to 28. Fatty acids are usually derived from...
s that humans and other animals must ingest because the body requires them for good health but cannot synthesize
Biosynthesis
Biosynthesis is an enzyme-catalyzed process in cells of living organisms by which substrates are converted to more complex products. The biosynthesis process often consists of several enzymatic steps in which the product of one step is used as substrate in the following step...
them. The term "essential fatty acid" refers to fatty acids required for biological processes, and not those that only act as fuel.
Only two EFAs are known for humans: alpha-linolenic acid
Alpha-linolenic acid
α-Linolenic acid is an organic compound found in many common vegetable oils. In terms of its structure, it is named all-cis-9,12,15-octadecatrienoic acid. In physiological literature, it is given the name 18:3 ....
(an omega-3 fatty acid
Omega-3 fatty acid
N−3 fatty acids are essential unsaturated fatty acids with a double bond starting after the third carbon atom from the end of the carbon chain....
) and linoleic acid
Linoleic acid
Linoleic acid is an unsaturated n-6 fatty acid. It is a colorless liquid at room temperature. In physiological literature, it has a lipid number of 18:2...
(an omega-6 fatty acid
Omega-6 fatty acid
n−6 fatty acids are a family of unsaturated fatty acids that have in common a final carbon–carbon double bond in the n−6 position, that is, the sixth bond, counting from the methyl end.The biological effects of the n−6 fatty acids are largely mediated by their conversion to n-6 eicosanoids...
). Other fatty acids that are only "conditionally essential" include gamma-linolenic acid
Gamma-Linolenic acid
γ-Linolenic acid is a fatty acid found primarily in vegetable oils...
(an omega-6 fatty acid), lauric acid
Lauric acid
Lauric acid , the saturated fatty acid with a 12-carbon atom chain, is a white, powdery solid with a faint odor of bay oil or soap.-Occurrence:...
(a saturated fatty acid), and palmitoleic acid
Palmitoleic acid
Palmitoleic acid, or -9-hexadecenoic acid, is an omega-7 monounsaturated fatty acid with the formula CH35CH=CH7COOH that is a common constituent of the glycerides of human adipose tissue. It is present in all tissues, but generally found in higher concentrations in the liver...
(a monounsaturated fatty acid).
When the two EFAs were first discovered in 1923, they were designated Vitamin F. In 1930, work by Burr, Burr and Miller on rats showed that the two EFAs are better classified with the fat
Fat
Fats consist of a wide group of compounds that are generally soluble in organic solvents and generally insoluble in water. Chemically, fats are triglycerides, triesters of glycerol and any of several fatty acids. Fats may be either solid or liquid at room temperature, depending on their structure...
s than with the vitamin
Vitamin
A vitamin is an organic compound required as a nutrient in tiny amounts by an organism. In other words, an organic chemical compound is called a vitamin when it cannot be synthesized in sufficient quantities by an organism, and must be obtained from the diet. Thus, the term is conditional both on...
s.
Functions
- The biological effects of the ω-3 and ω-6 fatty acids are mediated by their mutual interactions, see Essential fatty acid interactionsEssential fatty acid interactionsThe actions of the ω-3 and ω-6 essential fatty acids are best characterized by their interactions; they cannot be understood separately.Arachidonic acid is a 20-carbon ω-6 conditionally essential fatty acid...
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 eicosanoidEicosanoidIn biochemistry, eicosanoids are signaling molecules made by oxidation of twenty-carbon essential fatty acids, ....
s (affecting inflammationInflammationInflammation is part of the complex biological response of vascular tissues to harmful stimuli, such as pathogens, damaged cells, or irritants. Inflammation is a protective attempt by the organism to remove the injurious stimuli and to initiate the healing process...
and many other cellular functions) - the endocannabinoids (affecting mood, behavior and inflammation)
- the lipoxinLipoxinLipoxins are a series of anti-inflammatory mediators. Lipoxins are short lived endogenously produced nonclassic eicosanoids whose appearance in inflammation signals the resolution of inflammation....
s from ω-6 EFAs and resolvinsResolvinsResolvins are compounds that are made by the human body from the omega-3 fatty acids eicosapentaenoic acid and docosahexaenoic acid . They are produced by the COX-2 pathway especially in the presence of aspirin...
from ω-3 (in the presence of aspirin, downregulating inflammation.) - the isofuranIsofuranIsofurans are nonclassic eicosanoids formed nonenzymatically by free radical mediated peroxidation of arachidonic acid. The isofurans are similar to the isoprostanes and are formed under similar conditions, but contain a substituted tetrahydrofuran ring...
s, neurofuranNeurofuranNeurofurans are 22-carbon compounds formed nonenzymatically by free radical mediated peroxidation of docosahexaenoic acid , an ω-3 essential fatty acid. The neurofurans are similar to the isofurans and are formed under similar conditions of oxidative stress, containing a substituted...
s, isoprostaneIsoprostaneThe isoprostanes are prostaglandin-like compounds formed in vivo from the free radical-catalyzed peroxidationof essential fatty acids without the direct action of cyclooxygenase enzyme....
s, hepoxilinHepoxilinHepoxilins are nonclassic eicosanoid hormones involved in inflammation.-Biochemistry:They derive from arachidonic acid via oxidation by the enzyme 12-lipoxygenase...
s, epoxyeicosatrienoic acidEpoxyeicosatrienoic acidThe Epoxyeicosatrienoic acids or EETs are signaling molecules formed by the action of Cytochrome P450 epoxygenase on 20-carbon essential fatty acids, such as arachidonic acid, from which it is produced by the enzyme epoxygenase....
s (EETs) and Neuroprotectin DNeuroprotectinNeuroprotectin D1 is a docosanoid derived from the polyunsaturated fatty acid docosahexaenoic acid , which is a component of fish oil and the most important omega-3 PUFA. NPD1 exerts potent anti-inflammatory and anti-apoptotic bioactivity at nanomolar concentrations in a variety of experimental...
- the classic eicosanoid
- They form lipid raftLipid raftThe plasma membrane of cells is made of a combination of glycosphingolipids and protein receptors organized in glycolipoprotein microdomains termed lipid rafts...
s (affecting cellular signaling) - They act on DNA (activating or inhibiting transcription factors such as NF-κB, which is linked to pro-inflammatory cytokineCytokineCytokines are small cell-signaling protein molecules that are secreted by the glial cells of the nervous system and by numerous cells of the immune system and are a category of signaling molecules used extensively in intercellular communication...
production)
Fatty acids are straight chain hydrocarbons possessing a carboxyl
Carboxylic acid
Carboxylic acids are organic acids characterized by the presence of at least one carboxyl group. The general formula of a carboxylic acid is R-COOH, where R is some monovalent functional group...
(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 as a "ω", the last letter in the Greek alphabet
Greek alphabet
The Greek alphabet is the script that has been used to write the Greek language since at least 730 BC . The alphabet in its classical and modern form consists of 24 letters ordered in sequence from alpha to omega...
. 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
Stearidonic acid
Stearidonic acid is an ω-3 fatty acid, sometimes called moroctic acid. It is biosynthesized from alpha-linolenic acid by the enzyme delta-6-desaturase. Natural sources of this fatty acid are the seed oils of hemp, blackcurrant, corn gromwell and echium, and the cyanobacterium Spirulina....
) 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
Geometric isomerism
In organic chemistry, cis/trans isomerism or geometric isomerism or configuration isomerism or E/Z isomerism is a form of stereoisomerism describing the orientation of functional groups within a molecule...
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 acidPolyunsaturated fatty acidPolyunsaturated fatty acids are fatty acids that contain more than one double bond in their backbone. This class includes many important compounds, such as essential fatty acids and those that give drying oils their characteristic property....
s.
The essential fatty acids start with the short chain polyunsaturated fatty acids (SC-PUFA):
- ω-3 fatty acidOmega-3 fatty acidN−3 fatty acids are essential unsaturated fatty acids with a double bond starting after the third carbon atom from the end of the carbon chain....
s:- α-Linolenic acidAlpha-linolenic acidα-Linolenic acid is an organic compound found in many common vegetable oils. In terms of its structure, it is named all-cis-9,12,15-octadecatrienoic acid. In physiological literature, it is given the name 18:3 ....
or ALA (18:3)
- α-Linolenic acid
- ω-6 fatty acidsOmega-6 fatty acidn−6 fatty acids are a family of unsaturated fatty acids that have in common a final carbon–carbon double bond in the n−6 position, that is, the sixth bond, counting from the methyl end.The biological effects of the n−6 fatty acids are largely mediated by their conversion to n-6 eicosanoids...
:- Linoleic acidLinoleic acidLinoleic acid is an unsaturated n-6 fatty acid. It is a colorless liquid at room temperature. In physiological literature, it has a lipid number of 18:2...
or LA (18:2)
- Linoleic acid
These two fatty acids cannot be synthesised
Biosynthesis
Biosynthesis is an enzyme-catalyzed process in cells of living organisms by which substrates are converted to more complex products. The biosynthesis process often consists of several enzymatic steps in which the product of one step is used as substrate in the following step...
by humans, as humans lack the desaturase
Desaturase
A fatty acid desaturase is an enzyme that removes two hydrogen atoms from a fatty acid, creating a carbon/carbon double bond. These desaturases are classified as...
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 acidOmega-3 fatty acidN−3 fatty acids are essential unsaturated fatty acids with a double bond starting after the third carbon atom from the end of the carbon chain....
s:- eicosapentaenoic acidEicosapentaenoic acidEicosapentaenoic acid is an omega-3 fatty acid. In physiological literature, it is given the name 20:5. It also has the trivial name timnodonic acid...
or EPA (20:5) - docosahexaenoic acidDocosahexaenoic acidDocosahexaenoic acid is an omega-3 fatty acid that is a primary structural component of the human brain and retina. In chemical structure, DHA is a carboxylic acid with a 22-carbon chain and six cis double bonds; the first double bond is located at the third carbon from the omega end...
or DHA (22:6)
- eicosapentaenoic acid
- ω-6 fatty acidsOmega-6 fatty acidn−6 fatty acids are a family of unsaturated fatty acids that have in common a final carbon–carbon double bond in the n−6 position, that is, the sixth bond, counting from the methyl end.The biological effects of the n−6 fatty acids are largely mediated by their conversion to n-6 eicosanoids...
:- gamma-linolenic acidGamma-Linolenic acidγ-Linolenic acid is a fatty acid found primarily in vegetable oils...
or GLA (18:3) - dihomo-gamma-linolenic acidDihomo-gamma-linolenic acidDihomo-γ-linolenic acid is a 20-carbon ω−6 fatty acid. In physiological literature, it is given the name 20:3 . DGLA is a carboxylic acid with a 20-carbon chain and three cis double bonds; the first double bond is located at the sixth carbon from the omega end. DGLA is the elongation product...
or DGLA (20:3) - arachidonic acidArachidonic acidArachidonic acid is a polyunsaturated omega-6 fatty acid 20:4.It is the counterpart to the saturated arachidic acid found in peanut oil, Arachidonic acid (AA, sometimes ARA) is a polyunsaturated omega-6 fatty acid 20:4(ω-6).It is the counterpart to the saturated arachidic acid found in peanut oil,...
or AA (20:4)
- gamma-linolenic acid
ω-9 fatty acids
Omega-9 fatty acid
n−9 fatty acids are a family of unsaturated fatty acids which have in common a final carbon–carbon double bond in the n−9 position; that is, the ninth bond from the end of the fatty acid.-Background:Some n−9s are common components of animal fat and vegetable oil...
are not essential in humans, because humans generally possess all the enzymes required for their synthesis.
Essential fatty acids
Mammals lack the ability to introduce double bonds in fatty acids beyond carbon 9 and 10, hence ω-6 linoleic acid (18:2,9,12), abbreviated LA, and the ω-3 linolenic acidAlpha-linolenic acid
α-Linolenic acid is an organic compound found in many common vegetable oils. In terms of its structure, it is named all-cis-9,12,15-octadecatrienoic acid. In physiological literature, it is given the name 18:3 ....
(18:3,9,12,15), abbreviated ALA, are essential for humans in the diet. In humans, arachidonic acid (20:4,5,8,11,14) can be synthesized from LA by desaturation and chain elongation (though some carnivores like cats cannot do this, and require arachadonate in the diet). In addition, the human body can make some long-chain ω-3 PUFAs (EPA and DHA) from the ω-3 ALA.
Between 1930 and 1950, arachidonic acid
Arachidonic acid
Arachidonic acid is a polyunsaturated omega-6 fatty acid 20:4.It is the counterpart to the saturated arachidic acid found in peanut oil, Arachidonic acid (AA, sometimes ARA) is a polyunsaturated omega-6 fatty acid 20:4(ω-6).It is the counterpart to the saturated arachidic acid found in peanut oil,...
and linolenic acid
Alpha-linolenic acid
α-Linolenic acid is an organic compound found in many common vegetable oils. In terms of its structure, it is named all-cis-9,12,15-octadecatrienoic acid. In physiological literature, it is given the name 18:3 ....
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 for its class. 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. Conjugated
Conjugated system
In chemistry, a conjugated system is a system of connected p-orbitals with delocalized electrons in compounds with alternating single and multiple bonds, which in general may lower the overall energy of the molecule and increase stability. Lone pairs, radicals or carbenium ions may be part of the...
fatty acids like calendic acid
Calendic acid
Calendic acid is an unsaturated fatty acid, named for the pot marigold , from which it is obtained. It is chemically similar to the conjugated linoleic acids; laboratory work suggests it may have similar health benefits.-Biosynthesis:Calendic acid is an omega-6 fatty acid...
are not normally considered essential. Authoritative sources include the whole families, without qualification.
Traditionally speaking the LC-PUFA are not essential. See (Cunnane 2003) 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.
A 2005 study has shown evidence that the ω-6 fat gamma-linolenic acid, GLA
Gamma-Linolenic acid
γ-Linolenic acid is a fatty acid found primarily in vegetable oils...
has been shown to inhibit the breast cancer promoting gene of Her2/neu
HER2/neu
HER-2 also known as proto-oncogene Neu, receptor tyrosine-protein kinase erbB-2, CD340 or p185 is an enzyme that in humans is encoded by the ERBB2 gene. Over expression of this gene is correlated with higher aggressiveness in breast cancers...
.
Essential fatty acids should not be confused with essential oil
Essential oil
An essential oil is a concentrated hydrophobic liquid containing volatile aroma compounds from plants. Essential oils are also known as volatile oils, ethereal oils or aetherolea, or simply as the "oil of" the plant from which they were extracted, such as oil of clove...
s, which are "essential" in the sense of being a concentrated essence.
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
Fish
Fish are a paraphyletic group of organisms that consist of all gill-bearing aquatic vertebrate animals that lack limbs with digits. Included in this definition are the living hagfish, lampreys, and cartilaginous and bony fish, as well as various extinct related groups...
and shellfish
Shellfish
Shellfish is a culinary and fisheries term for exoskeleton-bearing aquatic invertebrates used as food, including various species of molluscs, crustaceans, and echinoderms. Although most kinds of shellfish are harvested from saltwater environments, some kinds are found only in freshwater...
, flaxseed (linseed)
Flax
Flax is a member of the genus Linum in the family Linaceae. It is native to the region extending from the eastern Mediterranean to India and was probably first domesticated in the Fertile Crescent...
, hemp oil
Hemp oil
Hempseed oil is pressed from the seed of the hemp plant irrespective of the strain of cannabis. Cold pressed, unrefined hemp oil is dark to clear light green in color, with a pleasant nutty flavor. The darker the color, the grassier the flavour....
, soya oil
Soybean
The soybean or soya bean is a species of legume native to East Asia, widely grown for its edible bean which has numerous uses...
, canola (rapeseed) oil, chia seeds
Salvia hispanica
Salvia hispanica, commonly known as chia, is a species of flowering plant in the mint family, Lamiaceae, native to central and southern Mexico and Guatemala. The 16th century Codex Mendoza provides evidence that it was cultivated by the Aztec in pre-Columbian times; it has been said that it was an...
, pumpkin seeds, sunflower seeds, leafy vegetables, and walnut
Walnut
Juglans is a plant genus of the family Juglandaceae, the seeds of which are known as walnuts. They are deciduous trees, 10–40 meters tall , with pinnate leaves 200–900 millimetres long , with 5–25 leaflets; the shoots have chambered pith, a character shared with the wingnuts , but not the hickories...
s.
Essential fatty acids play a part in many metabolic processes
Metabolism
Metabolism is the set of chemical reactions that happen in the cells of living organisms to sustain life. These processes allow organisms to grow and reproduce, maintain their structures, and respond to their environments. Metabolism is usually divided into two categories...
, 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
Osteoporosis
Osteoporosis is a disease of bones that leads to an increased risk of fracture. In osteoporosis the bone mineral density is reduced, bone microarchitecture is deteriorating, and the amount and variety of proteins in bone is altered...
.
Plant sources of ω-3 contain neither eicosapentaenoic acid
Eicosapentaenoic acid
Eicosapentaenoic acid is an omega-3 fatty acid. In physiological literature, it is given the name 20:5. It also has the trivial name timnodonic acid...
(EPA) nor docosahexaenoic acid
Docosahexaenoic acid
Docosahexaenoic acid is an omega-3 fatty acid that is a primary structural component of the human brain and retina. In chemical structure, DHA is a carboxylic acid with a 22-carbon chain and six cis double bonds; the first double bond is located at the third carbon from the omega end...
(DHA). The human body can (and in case of a purely vegetarian diet often must, unless certain algae
Algae
Algae are a large and diverse group of simple, typically autotrophic organisms, ranging from unicellular to multicellular forms, such as the giant kelps that grow to 65 meters in length. They are photosynthetic like plants, and "simple" because their tissues are not organized into the many...
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 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
National Institutes of Health
The National Institutes of Health are an agency of the United States Department of Health and Human Services and are the primary agency of the United States government responsible for biomedical and health-related research. Its science and engineering counterpart is the National Science Foundation...
's EFA Education group publishes 'Essential Fats in Food Oils.' This lists 40 common oils, more tightly focused on EFAs and sorted by n-6:3 ratio. list notable vegetable sources of EFAs as well as commentary and an overview of the biosynthetic pathways involved. Users can interactively search at 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 fatPolyunsaturated fat
In nutrition, polyunsaturated fat, or polyunsaturated fatty acid, are fatty acids in which more than one carbon–carbon 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...
s in the human diet are EFAs.
Essential fatty acids play an important role in the life and death of cardiac cells.
Essential fatty acid deficiency
Essential fatty acid deficiency results in a dermatitisDermatitis
-Etymology:Dermatitis derives from Greek derma "skin" + -itis "inflammation" and genetic disorder.-Terminology:There are several different types of dermatitis. The different kinds usually have in common an allergic reaction to specific allergens. The term may describe eczema, which is also called...
similar to that seen in zinc
Zinc deficiency
Zinc deficiency is insufficient zinc to meet the needs of biological organisms. It can occur in both plants and animals. Zinc deficient soil is soil in which there is insufficient zinc to allow plants to grow normally.-Description:...
or biotin deficiency
Biotin deficiency
Biotin deficiency is a rare nutritional disorder which can become serious, even fatal, if allowed to progress untreated. It can occur in people of any age, ancestry, or gender...
.
Treatment for depression
Research suggests that high intakes of fish and omega-3 fatty acids are linked to decreased rates of major depression. Omega-3 fatty acids, such as docosahexaenoic acidDocosahexaenoic acid
Docosahexaenoic acid is an omega-3 fatty acid that is a primary structural component of the human brain and retina. In chemical structure, DHA is a carboxylic acid with a 22-carbon chain and six cis double bonds; the first double bond is located at the third carbon from the omega end...
(DHA) and eicosapentaenoic acid
Eicosapentaenoic acid
Eicosapentaenoic acid is an omega-3 fatty acid. In physiological literature, it is given the name 20:5. It also has the trivial name timnodonic acid...
(EPA) are important for enzymatic pathways required to metabolize long-chain polyunsaturated fatty acids (PUFAs). Low plasma concentrations of DHA predict low concentrations of cerebrospinal fluid 5-hydroxyindoleacetic acid
5-Hydroxyindoleacetic acid
5-Hydroxyindoleacetic acid is the main metabolite of serotonin in the human body. In chemical analysis of urine samples, 5-HIAA is used to determine the body's levels of serotonin.- Clinical significance :...
(5-HIAA). It is found that low concentrations of 5-HIAA in the brain is associated with depression and suicide.
There are high concentrations of DHA in synaptic membranes of the brain. This is critical for synaptic transmission and membrane fluidity
Membrane fluidity
In biology, the membrane fluidity refers to the viscosity of the lipid bilayer of a cell membrane.The membrane phospholipids incorporate fatty acids of varying length and saturation...
. The omega-6 fatty acid
Omega-6 fatty acid
n−6 fatty acids are a family of unsaturated fatty acids that have in common a final carbon–carbon double bond in the n−6 position, that is, the sixth bond, counting from the methyl end.The biological effects of the n−6 fatty acids are largely mediated by their conversion to n-6 eicosanoids...
to omega-3 fatty acid
Omega-3 fatty acid
N−3 fatty acids are essential unsaturated fatty acids with a double bond starting after the third carbon atom from the end of the carbon chain....
ratio is important to avoid imbalance of membrane fluidity. Membrane fluidity affects function of enzymes such as adenylate cyclase
Adenylate cyclase
Adenylate cyclase is part of the G protein signalling cascade, which transmits chemical signals from outside the cell across the membrane to the inside of the cell ....
and ion channels such as calcium
Calcium
Calcium is the chemical element with the symbol Ca and atomic number 20. It has an atomic mass of 40.078 amu. Calcium is a soft gray alkaline earth metal, and is the fifth-most-abundant element by mass in the Earth's crust...
, potassium
Potassium
Potassium is the chemical element with the symbol K and atomic number 19. Elemental potassium is a soft silvery-white alkali metal that oxidizes rapidly in air and is very reactive with water, generating sufficient heat to ignite the hydrogen emitted in the reaction.Potassium and sodium are...
, and sodium
Sodium
Sodium is a chemical element with the symbol Na and atomic number 11. It is a soft, silvery-white, highly reactive metal and is a member of the alkali metals; its only stable isotope is 23Na. It is an abundant element that exists in numerous minerals, most commonly as sodium chloride...
, which in turn affects receptor numbers and functioning, as well as serotonin
Serotonin
Serotonin or 5-hydroxytryptamine is a monoamine neurotransmitter. Biochemically derived from tryptophan, serotonin is primarily found in the gastrointestinal tract, platelets, and in the central nervous system of animals including humans...
neurotransmitter levels. It is evident that western diets are deficient in omega-3 and excessive in omega-6, and balancing of this ratio would confer numerous health benefits.
Clinical research suggests a benefit of omega-3 fatty acids in the treatment of depression during the perinatal period. A meta analysis of trials of EPA supplements for depression in non-pregnant adults concluded that supplments with more than 60% EPA are effective, but those containing primarily DHA, or less than 60% EPA, were not effective.
See also
- Polyunsaturated fatPolyunsaturated fatIn nutrition, polyunsaturated fat, or polyunsaturated fatty acid, are fatty acids in which more than one carbon–carbon 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...
- Omega-3 fatty acidOmega-3 fatty acidN−3 fatty acids are essential unsaturated fatty acids with a double bond starting after the third carbon atom from the end of the carbon chain....
- Omega-6 fatty acidOmega-6 fatty acidn−6 fatty acids are a family of unsaturated fatty acids that have in common a final carbon–carbon double bond in the n−6 position, that is, the sixth bond, counting from the methyl end.The biological effects of the n−6 fatty acids are largely mediated by their conversion to n-6 eicosanoids...
- Essential fatty acid interactionsEssential fatty acid interactionsThe actions of the ω-3 and ω-6 essential fatty acids are best characterized by their interactions; they cannot be understood separately.Arachidonic acid is a 20-carbon ω-6 conditionally essential fatty acid...
- EicosanoidEicosanoidIn biochemistry, eicosanoids are signaling molecules made by oxidation of twenty-carbon essential fatty acids, ....
- ProstaglandinProstaglandinA prostaglandin is any member of a group of lipid compounds that are derived enzymatically from fatty acids and have important functions in the animal body. Every prostaglandin contains 20 carbon atoms, including a 5-carbon ring....
- LeukotrieneLeukotrieneLeukotrienes are fatty signaling molecules. They were first found in leukocytes . One of their roles is to trigger contractions in the smooth muscles lining the trachea; their overproduction is a major cause of inflammation in asthma and allergic rhinitis...
- ThromboxaneThromboxaneThromboxane is a member of the family of lipids known as eicosanoids. The two major thromboxanes are thromboxane A2 and thromboxane B2. The distinguishing feature of thromboxanes is a 6-membered ether-containing ring....
- Prostaglandin
- Nonclassic eicosanoidNonclassic eicosanoidNonclassic eicosanoids are biologically active signaling molecules made by oxygenation of twenty-carbon fatty acids other than the classic eicosanoids.-Terminology:"Eicosanoid" is the collective...
- Endogenous CannabinoidCannabinoidsCannabinoids are a class of chemical compounds that include the phytocannabinoids , and chemical compounds that mimic the actions of phytocannabinoids or have a similar structure...
- Essential nutrientEssential nutrientAn essential nutrient is a nutrient required for normal body functioning that either cannot be synthesized by the body at all, or cannot be synthesized in amounts adequate for good health , and thus must be obtained from a dietary source...
- Essential amino acidEssential amino acidAn essential amino acid or indispensable amino acid is an amino acid that cannot be synthesized de novo by the organism , and therefore must be supplied in the diet.-Essentiality vs. conditional essentiality in humans:...
- Fatty acid metabolismFatty acid metabolismFatty acids are an important source of energy and adenosine triphosphate for many cellular organisms. Excess fatty acids, glucose, and other nutrients can be stored efficiently as fat. Triglycerides yield more than twice as much energy for the same mass as do carbohydrates or proteins. All cell...
- Fatty acid synthaseFatty acid synthaseFatty acid synthase is an enzyme that in humans is encoded by the FASN gene.Fatty acid synthase is a multi-enzyme protein that catalyzes fatty acid synthesis...
- Oily fishOily fishOily fish have oil in their tissues and in the belly cavity around the gut. Their fillets contain up to 30 percent oil, although this figure varies both within and between species...