Three major types of omega-3 fatty acids
In this video, I’m going to talk about three major types of omega-3 fatty acids.
This slide shows the chemical structures of three major types of Omega-3 fatty acids or omega-3s. Omega-3 fatty acids have a carbon–carbon double bond located three carbons from the methyl end of the chain. The upper chemical structure in this slide is ALA which contains 18 carbons and 3 double bonds. The middle one is EPA which contains 20 carbons and 5 double bonds. The lower structure is DHA which contains 22 carbons and 6 double bonds.
ALA is an essential fatty acid because human body can not make ALA and it must be obtained from diet. Although ALA can be converted into EPA and then to DHA, the conversion rate is less than 15%. Therefore, in order to increase the levels of EPA and DHA in the body, people need to obtain EPA and DHA from foods and/or dietary supplements.
ALA is present in certain plants. Flaxseed oil, flaxseed, Chia seeds, walnuts, canola oil and soybean oil contain high amount of ALA.
In contrast, DHA and EPA are present in fish, fish oils, and krill oils. Fatty fish, such as salmon, herring, sardines, mackerel, trout etc. contain high amounts of DHA and EPA.
Because seafood contain relatively high amount of EPA and DHA, the 2015–2020 Dietary Guidelines for Americans recommend at least 8 ounces of seafood per week for adults. Women who are pregnant or breastfeeding should consume 8–12 ounces of seafood with higher EPA and DHA content per week. Fish with lower mercury levels such as salmon, herring, sardines, and trout are preferred over fish with higher mercury levels such as king mackerel, shark, swordfish, and tilefish.
Dietary supplements of EPA and DHA at no more than 5 g/day are considered safe when used as recommended.
This table provides the best choices of Fish that contain low mercury levels and the list of fish to avoid.
As shown in this table, the National Academy of Medicine has established the adequate intakes of omega-3 fatty acids for people of different age groups.
Most of the studies on the benefits of omega 3 fatty acids have focused on EPA and DHA.
Supportive evidence indicates that EPA and DHA may reduce the risk of coronary heart disease.
Omega-3 fatty acids in fish oils have been approved by the FDA as an adjunct to diet for reducing elevated triglyceride levels (at least 500 mg/dL [5.65 mmol/L]) in adults.
EPA and DHA may be helpful in alleviating the symptoms of rheumatoid arthritis.
The side effects of omega-3 supplements are usually mild. Common side effects include unpleasant taste, bad breath, odorous sweat, headache, heartburn, nausea, and diarrhea.