Nomenclature
Fatty acids are straight chain hydrocarbons possessing a carboxyl (COOH) group at one end. Biological fatty acids can be of different lengths, the last position is labelled as a "ω". 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). 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 ω-3 18:4 : 18-carbon chain with 4 double bonds, and with the first double bond in the third position from the CH3 end.
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) LA, and the ω-3 linolenic acid (18:3,9,12,15) ALA, are essential for humans in the diet. These two fatty acids cannot be synthesised by humans, as humans lack the desaturase enzymes required for their production. EFAs 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)
(ω-9 fatty acids (Oleic acid) are not essential in humans, because humans generally possess all the enzymes required for their synthesis)
These two fatty acids 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)
(Traditionally speaking, the LC-PUFAs are not essential. Because the LC-PUFA are sometimes required, they may be considered "conditionally essential", or not essential to healthy adults.)
Food Sources
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. Plant sources of ω-3 contain neither EPA nor DHA. The human body can convert α-linolenic acid (ALA) to EPA and subsequently DHA. This however requires more metabolic work.
Canola Oil
Canola oil is low in saturated fat and contains both omega-6 and omega-3 fatty acids in a ratio of 2:1. If consumed it also reduces Low-density lipoprotein and overall cholesterol levels, and as a significant source of the essential omega-3 fatty acid is associated with reduced all-cause and cardiovascular mortality. It is recognized by many health professional organizations including the American Dietetic Association and American Heart Association. Canola oil has been given a qualified health claim from the United States Food and Drug Administration due to its high levels of cholesterol-lowering fats.
Fatty acids are straight chain hydrocarbons possessing a carboxyl (COOH) group at one end. Biological fatty acids can be of different lengths, the last position is labelled as a "ω". 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). 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 ω-3 18:4 : 18-carbon chain with 4 double bonds, and with the first double bond in the third position from the CH3 end.
Essential fatty acids (EFAs)
EFAs refers to fatty acids required for biological processes, and not those that only act as fuel. Humans and other animals must ingest because the body requires them for good health but cannot synthesize them. There are two known EFAs 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).
The biological effects of the ω-3 and ω-6 fatty acids are mediated by their mutual interactions. In the body, essential fatty acids serve multiple functions:
- 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).
- They act on DNA (activating or inhibiting transcription factors such as NF-κB, which is linked to pro-inflammatory cytokine production).
- 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.
- 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. Modern Western diets typically have ratios of omega-6 to omega-3 in excess of 10 to 1, some as high as 30 to 1, partly due to corn oil which has an omega-6 to omega-3 ratio of 49:1. The optimal ratio is thought to be 4 to 1 or lower.
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) LA, and the ω-3 linolenic acid (18:3,9,12,15) ALA, are essential for humans in the diet. These two fatty acids cannot be synthesised by humans, as humans lack the desaturase enzymes required for their production. EFAs 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)
(ω-9 fatty acids (Oleic acid) are not essential in humans, because humans generally possess all the enzymes required for their synthesis)
These two fatty acids 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)
(Traditionally speaking, the LC-PUFAs are not essential. Because the LC-PUFA are sometimes required, they may be considered "conditionally essential", or not essential to healthy adults.)
Food Sources
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. Plant sources of ω-3 contain neither EPA nor DHA. The human body can convert α-linolenic acid (ALA) to EPA and subsequently DHA. This however requires more metabolic work.
Canola Oil
Canola oil is low in saturated fat and contains both omega-6 and omega-3 fatty acids in a ratio of 2:1. If consumed it also reduces Low-density lipoprotein and overall cholesterol levels, and as a significant source of the essential omega-3 fatty acid is associated with reduced all-cause and cardiovascular mortality. It is recognized by many health professional organizations including the American Dietetic Association and American Heart Association. Canola oil has been given a qualified health claim from the United States Food and Drug Administration due to its high levels of cholesterol-lowering fats.
