What are the 6 Key Omega-3 Fatty Acids & Their Benefits?

Omega-3 fatty acids are called “essential fatty acids”* by many in the global scientific community because while they support human health, the human body can’t effectively synthesize them from other fatty acids. You must get them from dietary sources.

Omega-3s are used in the structures of cell membranes, including in the brain, where they help to regulate the transmission of electrical impulses. They are also used by the body to make hormones that regulate inflammatory processes.

Here’s a breakdown of six of the most consumed and researched omega-3 fatty acids: their chemical structure, dietary sources, and roles in human health.†

ALA (alpha-linolenic acid) is the simplest and likely the most widely consumed omega-3 fatty acid.

ALA is the simplest of the omega-3 fatty acids, composed of an 18-carbon chain with three double-bonds, with the first double-bond stemming from the third carbon, which makes it an n-3, or omega-3. It can also be referred to by the shorthand 18:3 (n-3). A similar 18:3 fatty acid, but with the first double bond located at the sixth carbon, would be the omega-6 fatty acid gamma-linolenic acid, or GLA, with the shorthand 18:3 (n-6). Every omega-3 has an omega-6 counterpart, where the difference is the location of the first double bond.

ALA is found in a variety of common seed oils, including flaxseed, chia, canola, soybean, and walnut. ALA is unique under American nutritional and regulatory guidelines, as it is the only omega-3 recognized by the FDA as an essential fatty acid, with a recommended intake of 1.6 grams per day. In the US, foods that offer 160 mg of ALA (10% of recommended daily intake) per RACC (Reference Amount Customarily Consumed, meaning a typical single serving of a food) can be labeled as a “good source” of ALA. Foods that have 320 mg of ALA (20% recommended daily intake) per RACC can be labeled as a “high” or “excellent” source of ALA.

Much of the research relating to ALA has been focused on measuring the ability of the human body to convert it to DHA and EPA, which are of particular interest because of the cardiovascular and brain health benefits ascribed to them (see sections on DHA and EPA below). The human body can only convert about 2-5% of ALA to DHA, and 5-10% of ALA to EPA. Consequently, typical ALA consumption is not considered to be sufficient to produce appreciable amounts of DHA or EPA.

In recent years, researchers have sought to identify ALA’s direct health benefits. For instance, a 2012 study published in the American Journal of Clinical Nutrition found that dietary intake of ALA correlated with a modest reduction in the risk of cardiovascular disease, and that every 1 gram per day of ALA consumed was associated with a 10% lower risk of fatal coronary heart disease. It should be noted that the authors of this study were uncertain to whether the benefit was attributable to ALA, or to EPA produced from consumed ALA.

In another study of patients with high blood pressure given a high-flax diet (which is high in ALA) or a placebo, those who consumed large amounts of flax had significantly lower blood pressures than the placebo group after 6 months, with reductions of 15 mm Hg (systolic) and 7 mm Hg (diastolic).

EPA (eicosapentaenoic acid) is a long-chain omega-3 that is used by the body to reduce inflammation.

EPA is an LC-PUFA (long-chain polyunsaturated fatty acid), composed of a 20-carbon chain with five double bonds starting at the third carbon, written as 20:3 (n-3). EPA is produced by photosynthetic microalgae, which are in turn eaten by krill and fish, accumulating in their tissues. Fatty fish such as salmon, mackerel, anchovies, and sardines accumulate especially large amounts of EPA and other omega-3s in their tissues, which is why they are commonly used as sources of EPA and DHA in human nutrition and fish feeds.

Because EPA can typically only be consumed in fish or other marine sources, Western diets tend to be low in EPA. The body can synthesize small amounts of EPA from ALA in the liver, but the conversion rate is roughly 5% to 10%. It cannot generate anywhere close to the 500 to 1,000 mg of combined EPA and DHA recommended by many health organizations and scientific bodies around the world.

Most research on LC-PUFAs examines the correlation between EPA and DHA and human health, thus the benefits of EPA in isolation are still a matter of debate. However, purified EPA is sold as a prescription drug under the name Vascepa, and a large-scale double-blind study found that it reduced triglyceride levels, as well as the incidence of heart attacks and strokes when compared with a placebo.

DHA (docosahexaenoic acid) constitutes 5% to 10% of the human brain and is believed to contribute to the health of the brain, heart, eyes, and other parts of the body.

DHA is the most complex of the commonly studied omega-3s and is sometimes classified as a VLC-PUFA (very long-chain polyunsaturated fatty acid), with a 22-carbon chain and six double bonds starting at the third carbon and is notated as 22:6 (n-3).

DHA, like EPA, is produced by microalgae, though DHA is solely produced by species that are largely or entirely non-photosynthetic. These microalgae produce DHA by metabolizing free-floating elements in the water around them, such as carbon, nitrogen, and phosphorus. When DHA is produced commercially using microalgae, the microalgae is typically fed sugarcane. As with EPA, DHA is typically consumed via fatty fish or nutritional supplements derived from fish oil, krill oil, or algal oil.

The role of DHA in human health has been extensively studied for more than 75 years, including how it potentially supports heart health, brain development and health, child development, eye development and health, and aging. The body of research on DHA is expansive. Articles on our site cover many of these areas of focus in more detail.

DHA has anti-inflammatory effects which research suggests may reduce blood pressure, and the risk of heart disease and heart attacks, while also playing critical roles in the structure and function of the human brain, eyes, and muscles.

Potential benefits of maintaining high DHA levels highlighted in recent studies include:

DPA (docosapentaenoic acid) is a group of omega-3 and omega-6 fatty acids whose role in human health is an emerging area of research, with particular attention being paid to the omega-3 clupanodonic acid.

There are multiple omega-6 and omega-3 fatty acids with 22-carbon chains and five double bonds which are collectively referred to as DPA. However, DPA is often used to refer to the omega-3 clupanodonic acid, also written as 22:5 n-3, and from here will be used as such.

DPA is an intermediate omega-3 between EPA and DHA. The synthetization of DHA typically involves a process of omega-3s being converted into increasingly longer-chain fatty acids, culminating in EPA, then DPA, and finally DHA. DPA is typically found in the same dietary sources as DHA and EPA—salmon, anchovies, tuna, and other fatty fish—which they accumulate from microalgae and species that feed on microalgae.

Research conducted over the last three decades suggests that DPA plays a role in human health similar to DHA and EPA, reducing inflammation and triglycerides. Studies have also found that high levels of DPA correlate with a reduced risk of heart disease and death resulting from coronary heart disease.   

SDA (stearidonic acid) is an intermediate between ALA and EPA, and is naturally found in some plants.

SDA is an 18-carbon PUFA with four double bonds, starting from the third carbon, and thus can be notated as 18:4 (n-3). In addition to fish and algal oil, SDA is found in a few plants, including the herbs borage, Buglossoides, and Echium.

A key benefit of SDA is that it’s more easily converted by the body into EPA, compared to ALA. For ALA to synthesize into EPA, it must convert into SDA, then ETA (eicosatetraenoic acid), then EPA. Starting with SDA removes a step in this process. The conversion rate of SDA has been reported to be 17% to 41%, compared to the 5% to 10% conversion rate of ALA to EPA. SDA consumption increases DHA levels with similar effectiveness as ALA.

ETA (eicosatetraenoic acid) is the name of a group of 8 omega-3s and omega-6s, with one of these being all-cis-8,11,14,17-eicosatetraenoic acid, an intermediary between SDA and EPA.

ETA can be used to refer to any of 8 fatty acids which have a 20-carbon chain and four double bonds, the most notable of which is the omega-6 arachidonic acid (AA), which is found in cell membranes throughout the body, especially in cells making up the brain, muscles, and liver. The 20:4 (n-3) version of ETA is the rather laborious to pronounce all-cis-8,11,14,17-eicosatetraenoic acid (hereafter referred to as ETA), which is most notably found in green-lipped mussels.

Current understanding of ETA’s impact on human health is limited, beyond its role as an intermediary omega-3 between SDA and EPA. The modicum of research conducted on ETA suggests that it may have anti-inflammatory properties similar to other omega-3s.

* Currently in the United States, only ALA is considered essential to the diet, even though our bodies do not efficiently synthesize DHA and EPA from ALA.

† None of the information in this article is intended to promote the use of omega-3s to treat medical conditions. Consult with a doctor when considering taking omega-3s or related supplements to control or treat medical conditions.