What are omega-3 fatty acids?

Omega-3 fatty acids are among the most extensively researched nutrients — and at the same time among those most commonly lacking in Western diets. Whether for the heart, brain, eyes or the regulation of inflammation: these essential fatty acids play a central role in nearly every system of the body. This beginner's guide explains exactly what omega-3 fatty acids are, which types exist, why your body needs them, where to find them, and how much you should consume daily. Here you will get the basic knowledge you need to make well-informed decisions for your health — without marketing promises, but with concrete study references and EFSA-approved health claims.

What are omega-3 fatty acids? Definition and chemical basics

To truly understand omega-3 fatty acids, a brief look at biochemistry is helpful. Fats consist essentially of carbon chains with a carboxyl group at one end and a methyl group at the other.

The decisive difference lies in the molecular structure: in saturated fatty acids, all carbon atoms are linked by single bonds — the chain is "saturated" with hydrogen atoms. In unsaturated fatty acids, there are one or more double bonds between carbon atoms.

Omega-3 fatty acids are polyunsaturated fatty acids (PUFAs). The "omega-3" in their name describes the position of the first double bond: it is at the third carbon atom counted from the methyl end of the chain. In scientific nomenclature this is written as ω-3 or n-3. This seemingly small structural feature has far-reaching biological consequences — it influences how the fatty acid is incorporated into cell membranes, how flexible those membranes are, and which signalling molecules the body can derive from it.

By comparison: omega-6 fatty acids have their first double bond at the sixth carbon atom. Omega-9 fatty acids (such as oleic acid in olive oil) are not essential, as the body can produce them itself.

The omega-3 molecule, due to its specific geometry — the cis configuration of the double bonds creates a characteristic bend in the carbon chain — is particularly well suited to keeping cell membranes supple and permeable. It is precisely this property that makes omega-3 fatty acids so valuable for many bodily functions.

Another important characteristic: the human body cannot synthesise omega-3 fatty acids from other fatty acids. This makes them essential nutrients that must necessarily be obtained through the diet or dietary supplements. They share this property with few other nutrients such as certain amino acids and vitamins.

The three most important omega-3 fatty acids: EPA, DHA and ALA

Within the omega-3 family there are several different fatty acids, but three are of particular importance for human health: EPA, DHA and ALA. They differ in their chain length, their origin and their specific effects in the body.

EPA — Eicosapentaenoic acid: the anti-inflammatory fatty acid

EPA stands for eicosapentaenoic acid — an omega-3 fatty acid with 20 carbon atoms and five double bonds. It is found mainly in oily sea fish such as salmon, mackerel, herring and sardines. The name derives from the Greek word "eikosi" (twenty) and describes the chain length of the molecule.

EPA is particularly well known for its role in inflammation regulation. In the body, EPA is used as a precursor for so-called series-3 eicosanoids — local messenger substances such as prostaglandins, thromboxanes and leukotrienes. These series-3 eicosanoids generally act as anti-inflammatory and vasodilatory agents, in contrast to the series-2 eicosanoids formed from omega-6 fatty acids, which can have more pro-inflammatory effects.

In addition, EPA influences blood coagulation as it modulates platelet activation. According to EFSA, an intake of 250 mg of EPA+DHA daily contributes to normal cardiac function. EPA is also being intensively researched for its role in supporting mood regulation — several meta-analyses point to a positive association.

DHA — Docosahexaenoic acid: essential for brain and eyes

DHA, docosahexaenoic acid, with 22 carbon atoms and six double bonds, is the longest and most highly unsaturated of the three main omega-3 fatty acids. It is found in particularly high concentrations in the brain, retina and sperm cells — which already hints at its biological importance.

The human brain is made up of approximately 60% fat, and DHA accounts for a considerable proportion of this — especially in the phospholipids of neuronal cell membranes. An adequate supply of DHA is essential for signal transmission between nerve cells and the structural integrity of the brain. EFSA confirms that 250 mg of DHA daily contributes to normal brain function.

In the retina of the eye, DHA is the largest fat component. There it influences the function of rhodopsin, the light-sensitive protein in rod cells, and is thus directly involved in the processing of visual signals. EFSA has also approved a health claim for this function: 250 mg of DHA per day contributes to the maintenance of normal vision.

Especially during pregnancy and breastfeeding, an adequate supply of DHA is critical, as it significantly influences the development of the brain and eyes of the unborn child and newborn.

ALA — Alpha-linolenic acid: plant-based omega-3

ALA, alpha-linolenic acid, is the plant-based variant among the essential omega-3 fatty acids. It has 18 carbon atoms and three double bonds and is found abundantly in plant foods: linseed oil (up to 55% ALA), chia seeds (approximately 18% ALA), walnuts and hemp seeds. For vegans and vegetarians, ALA is often the primary omega-3 source from food.

The decisive problem with ALA: the human body can theoretically convert ALA into EPA and DHA, but this conversion rate is alarmingly low. Studies show that only about 5–15% of ingested ALA is converted to EPA. For DHA it is even worse: the conversion rate from ALA to DHA is below 1% — according to some studies as little as 0.5%.

This low conversion rate is influenced by various factors, including a high omega-6 to omega-3 ratio in the diet, genetic variations and general health status.

In practice this means: those who eat a purely plant-based diet can generally not meet their EPA and DHA requirements through ALA-rich foods alone. Targeted supplementation — ideally with algae oil as a vegan source of direct EPA and DHA — then becomes important. All the details are explained in the article Alpha-Linolenic Acid (ALA).

Why are omega-3 fatty acids essential?

The term "essential" has a precise meaning in nutritional science: it refers to nutrients that the body requires for vital functions but cannot produce on its own in sufficient quantities. In the case of omega-3 fatty acids, the human organism lacks the enzyme delta-15-desaturase, which would be needed to insert the critical double bond at the omega-3 position.

Once ingested, EPA and DHA are incorporated into the phospholipids of all cell membranes in the body. Membranes with a higher proportion of unsaturated fatty acids are more fluid and flexible — which improves the function of membrane-bound proteins, ion channels and receptors. This increased membrane fluidity is particularly decisive in highly specialised tissues such as the brain and retina.

In addition, EPA and DHA serve as precursors for eicosanoids and resolvins. Eicosanoids from EPA modulate inflammatory reactions, blood coagulation and immune responses. Resolvins actively promote the return to normality after an inflammatory reaction — a research field that has grown considerably in recent years.

For a comprehensive overview of the concrete health effects of an optimal omega-3 supply, it is worth consulting the health effects of omega-3, where individual organ systems and disease patterns are examined in detail.

EPA, DHA and ALA compared directly

Property	EPA	DHA	ALA
Full name	Eicosapentaenoic acid	Docosahexaenoic acid	Alpha-linolenic acid
Chain length	20 carbon atoms	22 carbon atoms	18 carbon atoms
Double bonds	5	6	3
Main sources	Oily sea fish, fish oil, krill oil, algae oil	Oily sea fish, fish oil, krill oil, algae oil	Linseed oil, chia seeds, walnuts, hemp seeds, rapeseed oil
Conversion to EPA	—	—	5–15%
Conversion to DHA	< 1%	—	< 1%
Main effects	Inflammation regulation, cardiac function, mood	Brain function, vision, development	Precursor for EPA/DHA (low rate)
EFSA Health Claim	250 mg EPA+DHA: normal cardiac function	250 mg DHA: normal brain function, normal vision	Essential nutrient (no specific claims)

The best sources of omega-3 fatty acids

Now you know what omega-3 fatty acids are and why you need them — but how do you best obtain them? Sources can broadly be divided into animal and plant sources, and the differences in bioavailability are considerable.

Animal sources: fish oil, oily fish, krill

By far the richest and most bioavailable sources of EPA and DHA are oily sea fish. At the top are Atlantic salmon, mackerel, herring, sardines and tuna. A single 150 g salmon steak can already deliver 2,000–3,000 mg of EPA+DHA — clearly more than the daily minimum recommendation. Anchovies, trout and sprats also belong to the EPA/DHA-rich fish varieties.

Why are fish so rich in omega-3 fatty acids? Ultimately because of the marine food chain: sea fish eat small crustaceans and zooplankton, which in turn have eaten microalgae. These microalgae are the true original producers of EPA and DHA in the sea.

Farmed salmon has often had a lower omega-3 content than wild salmon in recent years due to changes in feed (less fishmeal, more plant-based feed) — it is therefore worth checking the origin when purchasing.

Krill oil is another marine omega-3 source available in supplement form. The EPA and DHA in krill oil are partly bound as phospholipids, which according to some studies may improve bioavailability. However, the available amounts per capsule are often lower than in fish oil, and the evidence on superior bioavailability has not yet been conclusively established.

Plant sources: ALA in flaxseed, walnuts and chia seeds

For people who do not eat fish or prefer a plant-based diet, ALA-rich foods are the most accessible omega-3 source. Linseed oil leads here: it contains approximately 53–55% ALA and a single tablespoon (approx. 10 ml) already provides around 5,000 mg of ALA. However, the previously mentioned low conversion rate to EPA and DHA applies here.

Walnuts contain approximately 9% ALA relative to their total weight. A small handful of walnuts (30 g) provides about 2,500 mg of ALA. Chia seeds are also a concentrated ALA source with approximately 18% ALA. Other plant sources include hemp seeds, rapeseed oil and perilla oil. Important: heat damages polyunsaturated fatty acids. Linseed oil should therefore never be heated and is best used cold over salads or cottage cheese.

Despite the high ALA content in these foods, the central problem remains: the conversion to EPA and especially DHA is so low that purely plant-based omega-3 sources are generally not sufficient to cover EPA/DHA requirements.

Algae oil: the vegan alternative for EPA and DHA

The solution for vegans, vegetarians and everyone who does not like or cannot tolerate fish: algae oil. Since fish originally obtains its EPA and DHA from microalgae, it makes sense to go directly to this original source. Algae oil is derived from cultivated microalgae of the genera Schizochytrium, Crypthecodinium or Nannochloropsis and contains directly usable DHA — and depending on the algae species also EPA. It is the only plant source of directly bioavailable EPA and DHA and thus represents the optimal omega-3 supplement for a plant-based diet. Since the algae are grown under controlled conditions, the risk of heavy metal contamination is lower than with some fish oil products.

How much omega-3 do you need daily?

The question of the optimal omega-3 dosage is multifaceted, as it depends on the health goal, the individual baseline and the type of omega-3 fatty acid. The most reliable reference framework is the officially approved health claims of the European Food Safety Authority (EFSA), which are based on extensive study evaluations.

For the maintenance of normal bodily functions, EFSA recommends at least 250 mg of EPA+DHA per day for adults. This amount applies to normal cardiac function, normal brain function and the maintenance of normal vision. For specific health goals, higher amounts may be beneficial: for a contribution to normal triglyceride levels, 2,000 mg of EPA+DHA daily is required; for a contribution to normal blood pressure, even 3,000 mg daily.

In reality, the average omega-3 intake in Western countries is well below the recommended minimum — especially in people who rarely or never eat fish. For a personal assessment of your needs, our Omega-3 requirements calculator is available, which takes into account individual factors such as body weight, eating habits and health goals.

Omega-3 deficiency: common and often undetected

In Western industrialised societies, an insufficient omega-3 status is widespread — this is mainly due to a structural shift in diet. While our ancestors had an estimated omega-6 to omega-3 ratio of approximately 1:1 to 4:1, this ratio in the modern Western diet is 15:1 to 20:1. Industrially processed foods, sunflower and maize oils, and the low fish consumption of many people contribute to this imbalance.

A chronically low omega-3 status often manifests through a range of non-specific symptoms that are frequently attributed to other causes. Typical signs include dry, flaky skin and brittle nails and hair — as omega-3 fatty acids are important for the integrity of the skin barrier.

Other common symptoms are difficulty concentrating and memory problems, persistent joint and muscle pain, dry eyes, and frequent colds with a generally weakened immune system. Mood swings and increased irritability can also be associated with a low omega-3 status.

As these symptoms are non-specific, subjective assessment alone is insufficient. The safest way to check your own omega-3 status is a blood test — the so-called omega-3 index (EPA+DHA as a percentage of all fatty acids in red blood cells) is the most reliable marker.

An omega-3 index above 8% is considered optimal; below 4% is considered a risk zone. First take our quick Omega-3 deficiency check to assess whether you may be under-supplied.

Omega-3 supplements: when and how?

Those who do not meet their omega-3 needs through diet — whether due to preferences, intolerances, ethical reasons or simply the practical obstacles of daily fish consumption — can turn to supplements. On the market, three categories are most common: fish oil, krill oil and algae oil.

Fish oil is the most widely used and best-researched omega-3 supplement. It is derived from oily sea fish (usually anchovies, mackerel or sardines) and contains EPA and DHA in concentrated form. When choosing a fish oil, quality is critical: the TOTOX value (total oxidation value) provides information about the freshness of the oil — a low value is essential, as oxidised fish oil can not only be less effective but even counterproductive. A TOTOX below 26 is recommended. The form of delivery is also relevant: in the natural triglyceride form (TG), fish oil is more bioavailable than in the synthetic ethyl ester form (EE), which is found in many cheaper products.

Algae oil is the first choice for vegans and vegetarians, as well as for everyone who does not like the taste of fish oil. It delivers directly usable DHA and increasingly also EPA, without the detour through the marine food chain.

A detailed overview of quality criteria, ingredients and what to look out for when purchasing can be found in our Buying guide: What makes a good omega-3 oil? An overview of all the basics articles on omega-3 fatty acids is provided by the Basics overview.

Frequently asked questions about omega-3 fatty acids