Essential Fatty Acids: What They Are and Where to Find Them
- , by SANUSq Research team
- 13 min reading time
They are called essential fatty acids for a simple reason: your body cannot make them, so they have to come from food. Behind the name sits a family of fats in which the balance between omega-3 and omega-6 matters as much as the amount. Here is what they are, where to find them, and what large trials have shown about supplements.
What are essential fatty acids?
Strictly speaking, humans have only two truly essential fatty acids. The first is alpha-linolenic acid (ALA), the parent of the omega-3 family. The second is linoleic acid (LA), the parent of the omega-6 family. Everything else in these two families, including EPA, DHA and arachidonic acid, can in principle be made from those two parents. In practice, the body is not very good at it.
These fats are far more than a source of energy. They are built into the membranes of every cell, where they affect how flexible those membranes are and how well the receptors embedded in them work. They are also the raw material for signalling molecules that help regulate inflammation, blood clotting and the tone of blood vessels.
Broadly, mediators made from omega-6 fats tend to switch inflammatory responses on, while those made from omega-3 fats help resolve them. Both jobs are necessary.
Omega-3 and omega-6: a question of balance
This is the heart of the subject, and also where most of the confusion lies. Omega-3 and omega-6 fats are processed by the same enzymes, so they compete with each other. A diet heavy in omega-6, from sunflower, corn and grapeseed oils and many processed foods, keeps those enzymes busy and further limits the conversion of ALA into EPA and DHA, which is low to begin with.
You will often see a precise "ideal ratio" quoted, such as 4:1 or 1:1. Those figures are more a convenient shorthand than an established target. What can be said with confidence is that typical Western diets supply plenty of omega-6 and relatively little omega-3. The useful correction is not to cut out omega-6, which is essential too, but to eat more omega-3 and use a wider variety of oils.
Omega-6 fats have their own place in a healthy diet. Linoleic acid contributes to the maintenance of normal blood cholesterol levels, with the beneficial effect obtained from a daily intake of 10 g, an amount most people already reach without trying.
A Cochrane review by Hooper et al. (2018) pooled 19 randomised trials in 6,461 people who increased their omega-6 intake, usually in place of saturated or monounsaturated fats, for one to eight years. Higher omega-6 intake modestly lowered total cholesterol but made little or no clear difference to deaths or cardiovascular events overall.
Essential fatty acids foods: where to find them
Long-chain omega-3: EPA and DHA
The direct source of EPA and DHA is oily fish: sardines, mackerel, herring, salmon, trout and anchovies. Two portions a week cover most people's needs. Smaller fish such as sardines and anchovies tend to accumulate fewer contaminants.
Plant omega-3: ALA
ALA comes from plants. Good sources include:
- Oils — rapeseed (canola), linseed (flaxseed), walnut and sacha inchi oil.
- Nuts — walnuts in particular.
- Seeds — ground linseed, chia seeds and hemp seeds.
ALA contributes to the maintenance of normal blood cholesterol levels, with the beneficial effect obtained from a daily intake of 2 g. A tablespoon of rapeseed oil or a small handful of walnuts goes a good way towards that.
Oils rich in omega-3 oxidise quickly. Keep them cool and away from light, and use them raw rather than for frying. Grind linseeds, as whole ones tend to pass through undigested.
Omega-6: linoleic acid
Omega-6 needs no effort to find. It is in sunflower, corn, soya and grapeseed oils, in most nuts and seeds, and in a large share of processed and fried foods. The challenge is not getting enough but not overdoing it.
Conversion: the technical detail that matters
Here is the part most often glossed over. The body can turn ALA into EPA, and EPA into DHA, but it does so inefficiently. Only a small fraction of ALA becomes EPA, and even less becomes DHA. Women generally convert a little more than men.
Reviewing stable isotope tracer studies, Burdge and Calder (2005) found that conversion of ALA to EPA does occur but is limited in men, and that further conversion to DHA is very low. Eating more ALA for weeks to months raised EPA levels in the blood but did not raise DHA. Conversion was greater in women. The authors concluded that ALA is a limited source of longer-chain omega-3 fats.
A later review reached the same conclusion.
Baker et al. (2016) reviewed the metabolism of plant-derived omega-3 fats in humans. They described ALA as an essential fatty acid and the starting point for EPA and DHA, but noted that humans have limited capacity for this conversion, especially to DHA, and that seafood remains the primary source of EPA and DHA.
The practical consequence is clear. Someone who never eats fish will not meet their DHA needs from plant oils alone, however much they use. Plant sources are still worth having for the ALA itself, but they don't fully replace marine sources. For people who follow a vegan diet, microalgae are the only direct source of DHA.
In a two-week randomised study of 32 healthy adults, Arterburn et al. (2008) compared 600 mg a day of DHA from algal-oil capsules with the same amount from cooked salmon. DHA levels in blood plasma and red blood cells rose by similar amounts in both groups, indicating that algal oil delivers DHA as effectively as fish.
Why does DHA matter so much? DHA contributes to the maintenance of normal brain function and normal vision, and EPA and DHA together contribute to the normal function of the heart. In each case, the beneficial effect is obtained from a daily intake of 250 mg, which two portions of oily fish a week will provide for most people.
Omega-3 supplements: what the trials found
This is where marketing and the evidence part company most clearly. People who eat plenty of fish tend to have better heart health, but capsules tested in large trials have not matched that.
A Cochrane review by Abdelhamid et al. (2018) included 79 randomised trials with more than 112,000 participants, most taking omega-3 capsules. Increasing EPA and DHA made little or no difference to deaths or cardiovascular events, although it lowered triglycerides by around 15%. Low-quality evidence suggested that more ALA may slightly reduce cardiovascular events and irregular heart rhythms.
That does not mean omega-3 fats are useless. It means that taking capsules does not reproduce what is seen in people who eat oily fish regularly, perhaps because fish also brings protein, iodine, selenium and vitamin D, and takes the place of other foods on the plate.
In an updated review, Innes and Calder (2020) noted that long-term cohort studies consistently link higher fish and EPA/DHA intake with lower cardiovascular risk. They described the trial evidence in the general population as relatively weak, with more supportive results in some higher-risk groups under medical care.
You may also come across the omega-3 index, a blood test of EPA and DHA in red blood cells. Its role in everyday decisions is still debated.
von Schacky (2014) reviewed the omega-3 index and noted that, although large trials had not shown fewer cardiovascular events, higher blood levels of EPA and DHA were consistently associated with lower risk in observational studies.
Essential fatty acids in your diet: what actually helps
The order of priorities is simple:
- Eat oily fish twice a week. This covers EPA and DHA.
- Vary your oils. Use rapeseed and walnut oil regularly rather than sunflower oil for everything.
- Add nuts and seeds. Walnuts, ground linseed and chia are easy additions.
- Cut back on ultra-processed foods. They are the main source of surplus omega-6 in most diets.
Supplements come after that, mainly for people who don't eat fish. If you do choose one, look at the actual EPA and DHA content per serving rather than the total weight of oil on the label. A plant oil such as sacha inchi provides ALA, not EPA or DHA, so it is a way to add plant omega-3 rather than a direct substitute for fish.
A note on safety
High-dose omega-3 supplements can affect blood clotting. If you take a blood thinner such as warfarin, a newer anticoagulant or antiplatelet medicine such as aspirin or clopidogrel, talk to your doctor or pharmacist before taking omega-3 supplements, and mention them before any surgery or dental procedure. The same applies if you are pregnant, breastfeeding or have a medical condition.
Signs your intake may be too low
A true deficiency of essential fatty acids is rare in countries with a varied diet. When it does occur, it shows up as dry, scaly skin, slow wound healing and brittle hair. These signs have many other possible causes, so raise them with your doctor rather than assuming a fat shortfall.
The common situation is not deficiency but imbalance: plenty of omega-6, too little omega-3. That is not a diagnosis. It is a dietary pattern, and the steps above are the way to shift it.
Frequently asked questions
What are the two essential fatty acids?
Alpha-linolenic acid (ALA), an omega-3, and linoleic acid (LA), an omega-6. The body makes EPA and DHA from them only inefficiently.
What is the right balance of omega 3 and omega 6?
The two families share the same enzymes, so they compete. There is no firmly established ideal ratio. Western diets tend to be high in omega-6 and low in omega-3, so the sensible step is to eat more omega-3 and vary your oils, not to remove omega-6.
Which foods are richest in essential fatty acids?
Oily fish such as sardines, mackerel and salmon for EPA and DHA; rapeseed, linseed, walnut and sacha inchi oils, walnuts, ground linseed and chia seeds for ALA. Store omega-3-rich oils somewhere cool.
Are plant oils enough if I don't eat fish?
Not for DHA, because conversion from ALA is too low. Plant sources are still useful for ALA itself. If you follow a vegan diet, microalgae oil is the only direct plant-based source of DHA.
Should I take omega-3 capsules?
A Cochrane review of more than 112,000 participants found little or no effect of EPA and DHA capsules on deaths or cardiovascular events. Supplements may make sense if you don't eat fish; choose them on their real EPA and DHA content, and check with your doctor first if you take blood thinners.
What are the signs of essential fatty acid deficiency?
True deficiency is rare and can cause dry, scaly skin, slow wound healing and brittle hair. Far more common is an imbalance between omega-6 and omega-3, which is a matter of diet rather than a medical condition.
A plant source of omega-3
Sacha inchi oil in capsules — a plant source of omega-3 ALA, from the seeds of the sacha inchi plant.
Free shipping available — see current offers
References
- Hooper L, Al-Khudairy L, Abdelhamid AS, et al. Omega-6 fats for the primary and secondary prevention of cardiovascular disease. Cochrane Database of Systematic Reviews. 2018;11(11):CD011094. PMID 30488422
- Burdge GC, Calder PC. Conversion of alpha-linolenic acid to longer-chain polyunsaturated fatty acids in human adults. Reproduction Nutrition Development. 2005;45(5):581–597. PMID 16188209
- Baker EJ, Miles EA, Burdge GC, Yaqoob P, Calder PC. Metabolism and functional effects of plant-derived omega-3 fatty acids in humans. Progress in Lipid Research. 2016;64:30–56. PMID 27496755
- Arterburn LM, Oken HA, Bailey Hall E, et al. Algal-oil capsules and cooked salmon: nutritionally equivalent sources of docosahexaenoic acid. Journal of the American Dietetic Association. 2008;108(7):1204–1209. PMID 18589030
- Abdelhamid AS, Brown TJ, Brainard JS, et al. Omega-3 fatty acids for the primary and secondary prevention of cardiovascular disease. Cochrane Database of Systematic Reviews. 2018;11(11):CD003177. PMID 30521670
- Innes JK, Calder PC. Marine omega-3 (N-3) fatty acids for cardiovascular health: an update for 2020. International Journal of Molecular Sciences. 2020;21(4):1362. PMID 32085487
- von Schacky C. Omega-3 index and cardiovascular health. Nutrients. 2014;6(2):799–814. PMID 24566438
Read more on the blog
- Omega-3 for Heart Health →
- Sacha Inchi: A Complete Plant-Based Source of Omega-3 →
- The Anti-Inflammatory Diet: Best Foods and What to Avoid →
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