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Omega-3 Fatty Acids – Types, Structure, Sources, Functions

What is Omega-3 Fatty Acid?

  • Omega-3 fatty acids, also known as Omega-3 oils, ω-3 fatty acids, or n-3 fatty acids, are polyunsaturated fatty acids (PUFAs) distinguished by the presence of a double bond three atoms away from the terminal methyl group in their chemical structure. These fatty acids are crucial components of animal lipid metabolism and play a significant role in human physiology and diet.
  • There are three main types of omega-3 fatty acids that are essential for human health: α-linolenic acid (ALA), eicosapentaenoic acid (EPA), and docosahexaenoic acid (DHA). ALA is primarily found in plants, while DHA and EPA are found in algae and fish. Marine algae and phytoplankton are the primary sources of omega-3 fatty acids, with DHA and EPA accumulating in fish that consume these algae. Common sources of ALA include walnuts, edible seeds, flaxseeds, and hempseed oil, while EPA and DHA are found in fish and fish oils, as well as algae oil.
  • Mammals are unable to synthesize the essential omega-3 fatty acid ALA and must obtain it through their diet. However, they can convert ALA into EPA and DHA by adding double bonds along its carbon chain (desaturation) and extending it (elongation). The ability to convert ALA into the longer-chain omega-3 fatty acids may decrease with age. Unsaturated fatty acids, such as omega-3, are susceptible to oxidation and rancidity when exposed to air.
  • While there is some research suggesting that omega-3 fatty acid supplementation may reduce the risk of certain diseases, such as coronary heart disease, cancer, and cardiovascular disease, high-quality evidence is lacking. Studies on fish oil supplements have not consistently supported claims of preventing heart attacks, strokes, or other vascular disease outcomes.
  • The importance of omega-3 fatty acids was discovered in 1929 by George and Mildred Burr, who found that these fatty acids were critical to health and coined the term “essential fatty acids.” Since then, researchers have increasingly recognized the health benefits of omega-3 fatty acids, particularly for their role in forming cell membranes.
  • In 2004, the U.S. Food and Drug Administration acknowledged the potential health benefits of EPA and DHA omega-3 fatty acids, stating that “supportive but not conclusive research shows that consumption of EPA and DHA [omega-3] fatty acids may reduce the risk of coronary heart disease.” Similarly, the Canadian Food Inspection Agency recognizes the importance of DHA omega-3 in supporting the normal physical development of the brain, eyes, and nerves in children under two years of age.
  • Historically, whole food diets provided sufficient amounts of omega-3 fatty acids. However, the shift towards shelf-stable processed foods has led to a deficiency in omega-3 in manufactured foods due to its susceptibility to oxidation.

Definition of Omega-3 Fatty Acid

Omega-3 fatty acids are essential polyunsaturated fatty acids (PUFAs) characterized by a double bond three atoms away from the terminal methyl group in their chemical structure, crucial for human health, found in plants (as α-linolenic acid, ALA) and marine sources like algae and fish (as eicosapentaenoic acid, EPA, and docosahexaenoic acid, DHA).

Nomenclature of Omega-3 Fatty Acids

The nomenclature of omega-3 fatty acids is based on the location of the double bond closest to the methyl end of the molecule, following principles from organic chemistry. Here’s a breakdown of the nomenclature:

  1. Naming Convention:
    • ω−3 (“omega−3”) or n−3 (“n−3”) indicates the locant of the methyl end of the molecule.
    • The number n−x (or ω−x) refers to the locant of the nearest double bond from the methyl end.
    • In omega−3 fatty acids, the double bond closest to the methyl end is located at carbon 3 in the chain.
  2. Symbol Usage:
    • The symbol n (or ω) represents the locant of the methyl end, counted from the carboxyl end of the carbon chain.
    • For example, in an omega−3 fatty acid with 18 carbon atoms, where the methyl end is at location 18 from the carboxyl end, n (or ω) represents the number 18, and n−3 (or ω−3) represents 18−3 = 15, the locant of the double bond closest to the methyl end.
  3. Use of n vs. ω:
    • While n and ω are synonymous, the IUPAC recommends using n to identify the highest carbon number of a fatty acid.
    • However, the term omega−3 fatty acid is more commonly used in both lay media and scientific literature.


  • α-Linolenic acid (ALA) is an omega−3 fatty acid with an 18-carbon chain and three double bonds, with the first at the third carbon from the methyl end.
  • Counting from the carboxyl end, the three double bonds are at carbons 9, 12, and 15, indicated as Δ9c, Δ12c, and Δ15c or cisΔ9, cisΔ12, and cisΔ15.
  • ALA is polyunsaturated and described by the lipid number 18:3, indicating 18 carbon atoms and 3 double bonds.

This nomenclature system is valuable for understanding the structure and properties of omega-3 fatty acids in various contexts, including dietary and biochemical studies.

Structure of Omega-3 Fatty Acids

Omega-3 fatty acids are a group of polyunsaturated fatty acids that play crucial roles in human physiology. Understanding their chemistry is essential for appreciating their functions and effects on health. Here’s a breakdown of the chemistry of omega-3 fatty acids:

  1. Structure:
    • Omega-3 fatty acids have multiple double bonds in their carbon chain.
    • The first double bond is between the third and fourth carbon atoms from the end of the carbon chain, hence the term “omega-3.”
    • There are two types based on chain length:
      • Short-chain omega-3 fatty acids: Chain length of 18 carbon atoms or less.
      • Long-chain omega-3 fatty acids: Chain length of 20 carbon atoms or more.
  2. Important Omega-3 Fatty Acids:
    • α-linolenic acid (ALA): 18:3, n-3. It has 18 carbon atoms and 3 double bonds.
    • Eicosapentaenoic acid (EPA): 20:5, n-3. It has 20 carbon atoms and 5 double bonds.
    • Docosahexaenoic acid (DHA): 22:6, n-3. It has 22 carbon atoms and 6 double bonds.
    • These fatty acids are essential for human health and must be obtained from the diet.
  3. Double Bond Configuration:
    • Naturally-produced omega-3 fatty acids have double bonds in the cis-configuration.
    • In the cis-configuration, two hydrogen atoms are on the same side of the double bond.
    • The double bonds are interrupted by methylene bridges (-CH2-), ensuring two single bonds between each pair of adjacent double bonds.
  4. Oxidation Susceptibility:
    • Atoms at bis-allylic sites (between double bonds) are susceptible to oxidation by free radicals.
    • Substituting hydrogen atoms with deuterium atoms at these sites can protect omega-3 fatty acids from lipid peroxidation and ferroptosis, a form of regulated cell death.

Shelf life of Omega-3 Fatty Acids

  1. Susceptibility to Oxidation:
    • Omega-3 fatty acids are prone to oxidation when exposed to air, leading to a loss of nutritional value in the food.
    • This oxidation process can be accelerated by factors such as light, heat, and moisture, further reducing the shelf life of omega-3 fatty acids in foods.
  2. Storage Recommendations:
    • To preserve the nutritional quality of foods rich in omega-3 fatty acids, such as fish, eggs, meat, and seeds, it is advisable to store them in a cold and sealed environment.
    • Storing these foods in a cool place helps slow down the oxidation process and extends their shelf life.
  3. Optimal Consumption Time:
    • While proper storage can help extend the shelf life of omega-3 fatty acid-containing foods, it is generally recommended to consume them as soon as possible to ensure maximum nutritional benefits.
  4. Considerations for Storage:
    • Store omega-3 rich foods in airtight containers to minimize exposure to air and moisture.
    • Avoid storing these foods near heat sources or in direct sunlight to prevent accelerated oxidation.

Sources of Omega-3 Fatty Acids

Plant Sources of Omega-3 Fatty Acids:

  1. Flax Seeds and Flax Seed Oil: These are rich sources of ALA, a type of omega-3 fatty acid.
  2. Chia Seeds: Chia seeds are high in omega-3 fatty acids and also provide other nutrients like manganese and magnesium.
  3. Edamame: These are young soybeans and can be a source of omega-3 fatty acids.
  4. Soybean and Soybean Oil: Soy products contain omega-3s and are also rich in riboflavin, folate, and other nutrients.
  5. Walnuts: Walnuts are a plant-based source of omega-3 fatty acids and also provide fiber, copper, and vitamin E.
  6. Avocado: Avocado contains some omega-3 fatty acids, along with other beneficial nutrients.
  7. Oatmeal: Oatmeal can contribute to omega-3 intake, among other nutrients.
  8. Vegetables: Certain vegetables such as spinach, cauliflower, and Brussels sprouts contain small amounts of omega-3 fatty acids.
Plant SourcesOmega-3 ContentOther Nutrients
Flax Seeds and Flax Seed OilALA
Chia SeedsALAManganese, Magnesium
Soybean and Soybean OilALARiboflavin, Folate, Potassium, Vitamin K, Magnesium
WalnutsALAFiber, Copper, Vitamin E
Vegetables (Spinach, Cauliflower, Brussels Sprouts)ALA

Animal Sources of Omega-3 Fatty Acids:

  1. Fatty Fish: Fish like mackerel, salmon, herring, anchovy, tuna, oysters, halibut, sardines, bluefish, striped bass, and rainbow trout are rich sources of omega-3 fatty acids.
  2. Fish Oils: Fish oils, including egg oil, krill oil, and squid oils, are concentrated sources of omega-3 fatty acids.
  3. Caviar: Caviar, which consists of fish eggs or roe, is a good source of choline and omega-3 fatty acids.
  4. Anchovies: Anchovies are a good source of niacin, selenium, and omega-3 fatty acids.
Animal SourcesOmega-3 ContentOther Nutrients
Fatty FishEPA, DHAVarious nutrients depending on the fish
Fish Oils (Egg Oil, Krill Oil, Squid Oils)EPA, DHA
CaviarEPA, DHACholine
AnchoviesEPA, DHANiacin, Selenium

Benefits of omega-3 fatty acids

  1. Reduced Risk of Chronic Diseases:
    • Omega-3 fatty acids have been linked to a reduced risk of various chronic diseases, including cancer, obesity, strokes, pneumonia, and cardiovascular problems like heart disease.
  2. Cell Membrane Health:
    • Omega-3s help maintain the fluidity of cell membranes, which is essential for cellular communication and overall cell function.
  3. Anti-inflammatory Properties:
    • Omega-3s can reduce inflammation, which may help reduce symptoms of conditions like morning stiffness, swollen joints, ulcerative colitis, Crohn’s disease, psoriasis, and rheumatoid arthritis.
  4. Kidney Health:
    • Omega-3s may help prevent the formation of kidney stones.
  5. Mental Health Benefits:
    • Omega-3s are beneficial for mental health, helping to reduce symptoms of depression and anxiety, and improving mood and overall mental well-being.
  6. Hair and Skin Health:
    • Omega-3s provide nutrition to dry and damaged hair, helping to improve its condition. They also support skin health.
  7. Menstrual Health:
    • Omega-3s can reduce menstrual cramp pain.
  8. Brain Development and Cognitive Function:
    • Omega-3s are crucial for brain development and may enhance memory power and cognitive function.
  9. Cholesterol Management:
    • Omega-3s help maintain healthy cholesterol levels, reducing the risk of cardiovascular disease.
  10. Anti-inflammatory Effects:
    • Omega-3s, particularly those from marine sources, can lower blood inflammation markers.
  11. Appetite Control and Weight Management:
    • Omega-3 supplements can help control appetite and aid in weight management.
  12. Pregnancy and Child Development:
    • Omega-3s are important during pregnancy for brain health and cognitive development in the child, improving communication skills.
  13. Eye Health:
    • Omega-3s can improve eye health and reduce the risk of macular degeneration.
  14. ADHD Management:
    • Omega-3s may decrease the risk of attention deficit hyperactivity disorder (ADHD).
  15. Improved Sleep:
    • Omega-3s can promote good sleep quality.

Types of Omega-3 Fatty Acids

Omega-3 fatty acids are essential nutrients that play crucial roles in the human body, particularly in maintaining cardiovascular health, brain function, and inflammatory responses. There are three main types of omega-3 fatty acids: alpha-linolenic acid (ALA), eicosapentaenoic acid (EPA), and docosahexaenoic acid (DHA).

Omega-3 Fatty Acids - Types, Structure, Sources, Functions
  1. Alpha-linolenic acid (ALA):
    • ALA is a plant-derived omega-3 fatty acid, found in foods like flaxseed, soybean oil, chia seeds, walnuts, and algae oil.
    • It consists of 18 carbon atoms and three double bonds (C18:3n-3).
    • ALA is an essential fatty acid, meaning it must be obtained from the diet as the body cannot produce it.
    • While the body can convert some ALA into EPA and DHA, the conversion rate is limited, usually less than 15%.
    • ALA is primarily used by the body for energy.
  2. Eicosapentaenoic acid (EPA):
    • EPA is a long-chain omega-3 fatty acid found in fatty fish, fish oils, and krill oils.
    • It consists of 20 carbon atoms (C20:5n-3).
    • EPA is crucial for the proper functioning of the inflammatory system, which helps maintain the immune response.
    • Originally, EPA is synthesized by microalgae, and fish acquire it from their diet.
    • EPA can convert into DHA in the body.
  3. Docosahexaenoic acid (DHA):
    • DHA is another long-chain omega-3 fatty acid found in fatty fish, fish oil, meat, eggs, and dairy products from grass-fed animals.
    • It consists of 22 carbon atoms (C22:6n-3).
    • DHA is essential for the normal development and function of the brain, nervous system, retina, skin, testicles, and sperm.
    • It is highly present in the cell membrane of the retina, where it plays a crucial role in vision.
    • Unlike ALA, DHA is not present in significant amounts in vegetarian and vegan diets.
Omega-3 Fatty AcidSourceStructureFunction
Alpha-linolenic acid (ALA)Plant oils (flaxseed, soybean, canola), chia seeds, walnuts, algae oilC18:3n-3 (18 carbon atoms, 3 double bonds)Essential fatty acid; limited conversion to EPA and DHA; used for energy
Eicosapentaenoic acid (EPA)Fatty fish, fish oils, krill oilsC20:5n-3 (20 carbon atoms, 5 double bonds)Supports inflammatory system; precursor to DHA; originally synthesized by microalgae
Docosahexaenoic acid (DHA)Fatty fish, fish oil, meat, eggs, dairy (from grass-fed animals)C22:6n-3 (22 carbon atoms, 6 double bonds)Essential for brain, nervous system, retina, skin, testicles, sperm; not abundant in vegetarian/vegan diets

 Functions of Omega-3 Fatty Acids

  1. Cardiovascular Health: They decrease the aggregation of platelets, inhibit thickening of the arteries, and have antioxidant properties that protect cells from harmful substances, all of which are beneficial for cardiovascular health.
  2. Anti-inflammatory Effects: Omega-3s decrease the production of cytokines, which are messenger chemicals that promote inflammation. They have anti-inflammatory, immunomodulatory, hypolipidemic, anti-cancer, and hepatoprotective properties.
  3. Energy Production: Omega-3s provide energy to the body by transferring fatty acids into the mitochondria, which is crucial for maintaining a healthy cardiovascular and endocrine system.
  4. Vision: DHA (docosahexaenoic acid) and EPA (eicosapentaenoic acid) are crucial for vision. DHA alters signaling pathways that help regenerate rhodopsin and maintain healthy vision, while EPA serves as a precursor for signaling molecules important for retinal function.
  5. Triglyceride Reduction: Omega-3s reduce high triglycerides by influencing total body lipid accretion, which is important for metabolic health.
  6. Endothelial Function: They enhance the chemical activity derived from endothelial cells, leading to the production of nitric oxide, which causes arteries to relax and dilate, improving blood flow and reducing blood pressure.
  7. Transport of Substances: They transport calcium and other substances in and out of cells, contributing to cell function.
  8. Cell Membrane Structure: Omega-3 fatty acids are essential components of phospholipids, which are integral to cell membrane structure and function. They support the interaction between cells.
  9. Digestion: Omega-3s support digestion, aiding in the absorption of nutrients.
  10. Lipid Regulation: They lower lipid amounts, such as cholesterol, LDL (low-density lipoprotein), and triglycerides, circulating in the bloodstream, which is beneficial for heart health.
  11. Muscle Function: Omega-3s help in the movement of muscles, including relaxation and contraction.
  12. Blood Clotting: They prevent excessive blood clotting, which is crucial for cardiovascular health.
  13. Growth and Cell Division: Omega-3s play a role in growth and cell division processes in the body.

Causes of Omega-3 Deficiency

  • Dietary Insufficiency: Not consuming enough foods rich in omega-3 fatty acids is a primary cause of deficiency. These foods include fatty fish like salmon, mackerel, and sardines, as well as plant-based sources like flaxseeds, chia seeds, and walnuts.
  • Limited Conversion: While plant-based sources like flaxseeds and walnuts contain alpha-linolenic acid (ALA), a type of omega-3 fatty acid, the conversion of ALA into the more beneficial forms, eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), can be limited in some individuals. This limitation can result in lower levels of EPA and DHA, which are more readily used by the body.
  • Medical Conditions: Certain medical conditions can interfere with the absorption and utilization of omega-3 fatty acids. For example, digestive disorders like Crohn’s disease, celiac disease, and pancreatitis can affect the body’s ability to absorb nutrients, including omega-3s, from food.
  • Increased Omega-3 Requirements: Individuals with certain health conditions or lifestyles may have increased requirements for omega-3 fatty acids. This includes pregnant and lactating women, as well as athletes and those with high levels of physical activity.
  • High Omega-6 Intake: An imbalance between omega-6 and omega-3 fatty acids in the diet can also contribute to omega-3 deficiency. While both are essential, a high intake of omega-6 fatty acids, which are abundant in vegetable oils like soybean and corn oil, can interfere with the body’s utilization of omega-3s.

Symptoms of Omega-3 deficiency

  • Dry Skin: One of the earliest signs of omega-3 deficiency is dry, flaky skin. Omega-3 fatty acids help maintain the skin’s lipid barrier, which keeps it hydrated and healthy.
  • Joint Pain: Omega-3 fatty acids have anti-inflammatory properties. A deficiency can lead to increased inflammation, resulting in joint pain and discomfort.
  • Mood Swings: Omega-3s are crucial for mental health. A lack of these fatty acids can contribute to mood swings, depression, and anxiety. They play a role in neurotransmitter function and brain health.
  • Fatigue: Inadequate levels of omega-3 fatty acids can lead to reduced energy levels and increased fatigue, affecting overall productivity and well-being.
  • Cardiovascular Problems: Omega-3s are essential for heart health. A deficiency can increase the risk of cardiovascular issues, including high blood pressure and heart disease.
  • Weight Gain and Obesity: Omega-3 deficiency may contribute to weight gain and obesity, as these fatty acids are involved in regulating metabolism and fat storage.
  • Cognitive Decline: A lack of omega-3 fatty acids can affect brain health, potentially leading to conditions like Alzheimer’s disease and poor memory.
  • Depression and Mood Swings: The deficiency can exacerbate symptoms of depression and lead to significant mood swings, affecting overall mental health.
  • Joint Pains and Cramps: Due to their role in reducing inflammation, a lack of omega-3s can lead to increased joint pains and cramps.
  • Increased Cholesterol Levels: Omega-3 fatty acids help regulate cholesterol levels. Deficiency can result in higher levels of bad cholesterol (LDL) and lower levels of good cholesterol (HDL).
  • Autoimmune Diseases: Omega-3 deficiency can contribute to the development of autoimmune diseases, where the immune system mistakenly attacks healthy cells.
  • Rough, Scaly Skin and Dermatitis: Insufficient omega-3s can cause rough, scaly skin and conditions like dermatitis due to their role in skin health.
  • Sleep Deprivation: Omega-3 fatty acids are important for healthy sleep patterns. A deficiency can lead to sleep disturbances and deprivation.
  • Improper Brain Development and Functioning: In children, a lack of omega-3s can result in improper brain development, potentially leading to conditions like Parkinson’s disease and cognitive impairments.


  • Tur JA, Bibiloni MM, Sureda A, Pons A (June 2012). “Dietary sources of omega 3 fatty acids: public health risks and benefits”. The British Journal of Nutrition. 107 (Suppl 2): S23-52. doi:10.1017/S0007114512001456. PMID 22591897.

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