Omega-3

The importance of a diet with sufficient omega-3 fatty acids concentration: EPA, DHA and SDA

Definition

Fatty acids are absorbable units of fat. They are carboxylic acids that have an even number of carbon atoms (between four and twenty-four) and their classification is made on the basis of chain length, structure and the position of the first double bond. 

Depending on their chain length, they are called short chain (18 or fewer carbon atoms) or long chain (20 or more carbon atoms). 

According to their chemical structure, fatty acids are classified as monounsaturated, polyunsaturated and saturated fats

  • Monounsaturated fatty acids have only one double bond (unsaturated) in their chain, are likely to be liquid at room temperature and olive oil is one of their principal sources. 
  • Polyunsaturated fatty acids have two or more double bonds (unsaturated) in their chain and are found in seed oils and fish, especially oily fish. 
  • Saturated fatty acids have no double bonds (saturated) in their chain and are usually solid at room temperature. An excessive intake leads to increased risk of cardiovascular disease. Lard, for example, is a type of saturated fat. 

Depending on the position of the first double bond, fatty acids can be classified into three series: omega-3 (n-3) when the first double bond is in the 3rd position from the methyl end, omega-6 (n-6) and omega-9 (n-9) when this double bond is in the 6th or 9th position, respectively, from the methyl end.

Types of omega-3 fatty acids

Omega-3 fatty acids are polyunsaturated essential fatty acids (so called because the human body cannot produce them). Among them are those known as eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), which are found in very high proportion in the tissues of certain fish (mainly oily fish), and alpha-linolenic acid (ALA), which is found primarily in plant sources such as flax seeds, chia seeds, Sacha Inchi (48% omega-3), hemp seeds and walnuts. 

An intake of sufficient amounts of omega-3 fatty acids has been experimentally shown to provide beneficial effects on health, which explains why the incidence of cardiovascular disease, among others, is so low in communities that consume many omega-3 rich foods (Eskimos, Japanese, etc.).

Short chain omega-3 fatty acids

Fatty acids are classified as essential according to the position of the first double bond, counting from the methyl group (-CH3) located at the end of the alkyl group chain (-CH2). Mammals do not have the enzymes needed for synthesizing double bonds in positions n-3 and n-6 of fatty acids, which is why they need to get alpha-linolenic and linoleic essential fatty acids through the diet. 

Fatty acids of plant origin have fewer than 18 carbon atoms and are called short chain fatty acids. 

Alpha-linolenic acid (short chain omega-3 fatty acid) is found in plants, in significant amounts in flax and canola seeds, among others. The human body, like those of other animals, produces derivatives from alpha-linolenic acid that contain a higher number of carbon atoms. Alpha-linolenic acid has significant biological effects and helps in the prevention and treatment of some chronic diseases, acts on inflammation (a characteristic of many of these diseases) and promotes healthy blood vessel function, thereby reducing the risk of heart attack and stroke. 

Alpha-linolenic acid constitutes between 75% and 80% of total omega-3 fatty acids in mother's milk, which is very important for the growth and development of children. Alpha-linolenic acid is also necessary to maintain proper nervous system function, and a lack of it in humans can cause poor growth, numbness, pain in the legs, walking difficulties and blurry vision. 

Long chain omega-3 fatty acids (LC-PUFA)

The action of desaturase and elongase enzymes allows to obtain derivatives of biological significance from omega-3, omega-6 and omega-9 series of fatty acids. More specifically, from alpha-linolenic acid (omega-3) we can get eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). 

EPA contains 20 carbon atoms and 5 double bonds (20:5), and DHA contains 22 carbon atoms and 6 double bonds (20:6); they are what we know as long chain omega-3 fatty acids. Epidemiological, human intervention and experimental studies attribute properties that are very beneficial for health to long chain omega-3 fatty acids because they are effective in the primary and secondary prevention of a number of diseases, such as cardiovascular disease. Omega-3 fatty acids may have antiatherosclerotic, antithrombotic, anti-arrhythmic, anticancer and anti-inflammatory effects, as well as a actions on nervous system function, among other properties. The mechanisms of action range from structural changes in cell membranes to regulation of gene expression. Taking their rapid rate of metabolic assimilation into account, the observation of the association between these diseases and EPA and DHA deficiency confers greater importance on clinical nutrition support based on omega-3 fatty acids.

Sources of omega-3 fatty acids

Flaxseed oil is considered to be the richest plant source of alpha-linolenic acid (57% of total fatty acids). Rapeseed, soybeans, wheat germ and walnuts have between 7% and 13% of this type of acid. Some authors believe that vegetables are a good source of alpha-linolenic acid (e.g. spinach, lettuce), although their fatty content is quite low. 

As for EPA and DHA, the richest sources are fish oils and oily fish. The high content of DHA and EPA in fish is due to their feeding on phytoplankton (which is rich in omega-3 polyunsaturated fatty acids), which helps fish adapt to cold water. The omega-3 polyunsaturated fatty acids content varies according to the fish species, their location, the season of the year, and the availability of phytoplankton.

Physiological roles of omega-3 in the body

In human beings, omega-3 fatty acids are important in maintaining the structure of cellular membranes, improving absorption of liposoluble vitamins (A, D, E and K), regulating cholesterol metabolism and producing eicosanoids, which regulate various cellular processes (vascular and bronchial tone, gastrointestinal and uterine motility, gastric protection, urine output, blood clotting, body temperature, inflammatory and immune processes, etc.). 

The triglyceride-lowering effects of omega-3 fatty acids are due to: 

  • Reduction hepatic synthesis of triglycerides and very low-density lipoproteins (VLDL), as eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) are bad substrates for the enzymes responsible for triglyceride synthesis, and also inhibit the esterification of other fatty acids needed for triglyceride synthesis.
  • Increase of hepatic peroxisomal fatty acid beta-oxidation, thereby lowering their availability for VLDL synthesis.
  • Inhibition of the activity of the acyl-CoA:1,2-diaglycerol acyltransferase enzyme that takes part in triglyceride synthesis.
  • Inhibition of synthesis and secretion of kilomicrons and acceleration of postprandial reduction of triglyceride concentrations.

The improvement of omega-3 fatty acids in endothelial function has been attributed to their ability to augment nitric oxide release by the endothelial cells. Omega-3 fatty acids inhibit platelet aggregation, especially that induced by collagen, and the production of thromboxane A2 (TXA2), so that their administration could result in a prolonged bleeding time.

Omega-3 fatty acids become incorporated into cell membranes and can act as substrate for cyclooxygenases and lipoxygenase, thereby suppressing the synthesis and plasma concentration of 2-series thromboxane and prostacyclins and 4-series leukotrienes, which have pro-aggregation, vasoconstriction and pro-inflammatory effects.

Omega-3 fatty acids also show anti-inflammatory properties by reducing C reactive protein levels. 

The hypolipemiant and anti-inflammatory effects of EPA and DHA may be related to their ability to perform as ligands of the peroxisome proliferator activated receptors (PPAR-a), which regulate several genes that participate in lipid metabolism. 

Omega-3 fatty acids hyperpolarize membrane potential, which increases the ventricular excitability threshold and prolongs the duration of the refractory period, resulting in two of the effects of its anti-arrhythmic properties.

Omega-3 fatty acids are components of the phospholipids that make up cell membranes, which is why they are essential to the growth of nervous system tissue during pregnancy, breastfeeding and infancy.

Omega-3 in high concentration

Fish is the primary source for omega-3 fatty acids in human diet. Fish from species such as tuna, sardines and salmon are those that have the highest percentage of long chain omega-3 fatty acids DHA and EPA (from 0.24 g/100 g in tuna to 1.10 g/100 g in mackerel). Traditional processes to obtain fish oil involve two phases: extraction of the oil from the fish and then refining it. Using this method, the concentration of EPA and DHA thus obtained can vary between 19.8% and 40.5% of the total fatty acids in the supplement. 

In order to obtain a greater concentration of omega-3 fatty acids DHA and EPA from the raw material, new methods of extraction, such as supercritical fluid extraction, have been developed. A fluid is considered to be in supercritical state when, by keeping it at a certain temperature, pressure and density, it is in a phase where its properties are halfway between those of a liquid and a gas. At this point its density is similar to that of liquids and at the same time, its viscosity and diffusivity are gas-like. These supercritical fluids have high solvent power and are able to separate the different fatty acids in fish in order to obtain high concentrations of each one of them based on their molecular weight. The most commonly used supercritical fluid is carbon dioxide, which is considered a "green solvent", as it is non-toxic, inexpensive and non-flammable. 

Through the use of this technique, it is possible to obtain concentrations of 90% pure omega-3 fatty acids EPA and DHA (95% of EPA and more than 80% of DHA). The result is a product that is highly efficacious and safer, as virtually 100% of the toxins, such as dioxins, present in the fish, are eliminated. 

The concentration strength of long chain omega-3 fatty acids (DHA and EPA) in supplements is very important, as it has been shown that these fatty acids are absorbed faster and that a higher proportion are incorporated into plasma phospholipids than when they are ingested at lower concentrations, even if the total amount of omega-3 fatty acids ingested is the same. Furthermore, this greater absorption and incorporation into plasma phospholipids translates into higher efficacy, as has been shown by the reduction of plasma triglycerides and cholesterol in persons who were taking them in high concentrate supplements (85% against 62,5%).

Glossary

Adipokine. Hormone from the anterior lobe of the hypophysis that causes the mobilization of fat from adipose tissue.

Atheromatous plaque. A mass of lipids and other substances that tend to be deposited in the shape of plaques on the walls of an artery.

Cytokines. Proteins that regulate the functional activities of the cells that produce them or those of other cells. They mediate interactions between cells, induce activation of specific receptors in the membrane, promote cellular proliferation and differentiation, induce chemotaxis, growth and modulation of immunoglobulin secretion. 

DHA. Docosahexaenoic acid. Omega 3 polyunsaturated fatty acid found in fish fat. 

Dyslipidemia. Alteration of the lipid pattern.

Eicosanoids. Group of lipid molecules that are produced by the oxygenation of omega 3 and omega 6 type 20-carbon essential fatty acids. All eicosanoids are classified into prostaglandins, thromboxanes, leukotrienes and some hydro acids that are precursors to the leukotrienes. 

Enteral nutrition. Method of delivering nutrients to the body through the digestive system.

EPA. Eicosapentaenoic acid. Omega 3 polyunsaturated fatty acid. It is found primarily in fish fat.

Essential fatty acid. Fatty acids indispensable for the body. They must be ingested from food because the body cannot produce them. Linoleic acid and linolenic acid are essential.

Fatty acid. Absorbable unit of fat. Fairly wide group of series of carbon atoms that are linked together. The classification of fatty acids is based upon the nature of the bonds and the length of the molecule. 

Interleukin. Name given to cytokines produced by lymphocytes.

Leukotrienes. Fatty acids derived from arachidonic acid by oxidative metabolism through the 5-lipoxygenase pathway. 

Lipids. Chemical substances of widely varied composition that are insoluble in water. They are made almost exclusively of carbon, hydrogen and oxygen. 

Lipogenesis. Lipid anabolism. Process in which fatty acids are synthesized and esterified with glycerol to form triglycerides for storage. 

Lipolysis. Lipid catabolism. Process in which body lipids are hydrolyzed into glycerol and free fatty acids, and in this way provide for energy needs.

Linoleic acid. C18:2, of the omega 6 series. Essential fatty acid that has two unsaturated bonds. Found primarily in the seed oils: sunflower, corn, grapeseed, etc. 

Linolenic acid. C18:3, of the omega 3 series. Found in some vegetable oils such as soy and rapeseed oils. Also found in walnuts, flax seeds, soy beans and soy products.

Monounsaturated fatty acid. Fatty acid in which there is one double bond (unsaturated) in its chain. Likely to be liquid at room temperature. Found in olive oil. 

Oleic acid. Olive oil is the main dietary source of this monounsaturated fatty acid. 

Omega 3 fatty acids. Polyunsaturated fatty acids that contain their first double bonds between carbons 3 and 4 from the methyl end of the fatty acid. They are considered to be protectors of the cardiovascular system and are found mainly in the fat of oily fish. 

Omega 6 fatty acids. Polyunsaturated fatty acids that contain their first double bonds between carbons 6 and 7 from the methyl end of the fatty acid. They are found mainly in nuts and seeds.

Parenteral nutrition. Method of delivering nutrients to the body through a system other than the gastrointestinal tract. 

Peptide. Molecule consisting of two or more amino acids. They are intermediate products of protein digestion. They are a dietary nitrogen source. 

Placebo. A pharmacologically inactive substance. It may have a psychological effect.

Polyunsaturated fatty acid. Fatty acid in which there are two or more double bonds (unsaturated) in its chain. Found in seed and fish oils. 

Postprandial. Situation of the the body after the ingestion of a specific nutrient. 

Prostaglandins. Compounds produced from both omega 3 and omega 6 unsaturated fatty acids; they are extremely potent mediators in numerous physiological processes.

Saturated fatty acid. Fatty acid that has no double bonds (saturated) in its chain. Likely to be solid at room temperature. A high intake is related to increased risk of cardiovascular disease. Found, for example, in lard.

Stearic acid. Saturated fatty acid found in animal fat.

Thromboxane. Each one of the two derivatives of prostaglandins that are related to arachidonic acid. Thromboxane A2 (TXA2) is a very powerful inducer of platelet aggregation and also has vasoconstrictive properties; it acts as a physiological antagonist of prostacyclin. It is synthesized by platelets and is rapidly non-enzymatically hydrolyzed to thromboxane B2, which is inactive (TXB2).

Trans fatty acid. Spatial structure that double bonds can adopt. They occur naturally in the milk and meat of ruminants. They are also produced when natural fatty acids with double bonds are subjected to certain technological processes such as hydrogenation, oil refining, etc. They tend to accumulate in various tissues. Their hypercholesterolemic effect has been shown.