The omega alphabet: what 3, 6, 7 and 9 actually do

A quick, honest heads-up: this is by far the longest piece on this site, about a 17-minute read. I genuinely tried to make it shorter, but this topic deserves the nuance. Take your time; it’s worth it.

When I started, I had expectations. No miracles, but something. More energy. A sharper mind. Or just the quiet feeling that I was doing something good for myself.

After a few months, an uncomfortable question surfaced.

Do I actually feel a difference?

The quiet trap in my own head

Before we get to the science, I have to admit something. About myself and, honestly, about all of us.

There is a psychological phenomenon called cognitive dissonance. Put simply: we badly want to believe our choices were sensible. We remember the days we feel good. We forget the tired days. We tie the good feeling to the product.

Not because we want to fool ourselves. But because that is simply how the brain works.

What does such a number actually mean?

“Omega” simply refers to where in the fatty-acid chain the first double bond sits, counted from the end of the chain furthest from the acid group. Omega-3 has that bond at the third position, omega-6 at the sixth, omega-9 at the ninth. So it is not a quality seal and not a ranking, it is a spot on a molecule. Nothing more.

Within “omega 3” there are, in turn, different fatty acids. The two that science almost always cares about are EPA (eicosapentaenoic acid) and DHA (docosahexaenoic acid), both with long, polyunsaturated chains. A third, ALA (alpha-linolenic acid), is the plant-based variant from flaxseed and walnuts, and serves mainly as a raw material: the body can make a little EPA and DHA from it, but that conversion is inefficient.

What is genuinely not up for debate?

EPA and DHA sit in the walls of your cells, in your brain, in your nerves and in the retina of your eyes. That is biology. In fact: why evolution chose these two molecules in particular is a lovely story in itself. Cell membranes are not rigid plastic; they have to move, bend, fuse and pass on signals. The double bonds in EPA and DHA keep membranes supple enough to do that. That is why the brain in particular, where signals must travel at lightning speed, contains relatively high amounts of DHA. An overview of this role in the brain can be found in Dighriri et al. (2022) in Cureus.

But here a thinking error often slips in.

That something is important for your body does not automatically mean an extra scoop brings benefit. Water is important. Sleep is important. But if you already get enough, more does not make you healthier.

Why can’t my body just make them itself?

A logical follow-up: if EPA and DHA are so important, why doesn’t my body make them itself, as it does with so many other substances?

The answer lies in a conversion chain: ALA → EPA → DHA. Humans have the enzymes to carry out that conversion, but they work slowly and inefficiently: only a small part of the ALA you eat ends up in your tissues as EPA or DHA. That is probably also why oily fish played such a big evolutionary role: algae make EPA and DHA directly, fish eat those algae (or eat other fish that ate the algae), and we eat the fish. Almost all the EPA and DHA on our plate therefore comes, via a few links, from the ocean.

So what does science really say, about omega 3?

Here it gets more nuanced than the brochure. I’ll split it honestly in two.

Where the evidence is strongest. Omega 3 demonstrably lowers triglycerides, a certain type of fat in your blood and that effect grows with higher doses (Wang et al., 2023, Journal of the American Heart Association). There is also benefit in specific groups: people who already have heart problems or a high risk, and people who eat little fish. High-dose, pure EPA shows the clearest results there (Yang et al., 2022, Progress in Lipid Research). Importantly: this is the doctor’s territory, not the shelf in the shop.

Where the evidence is actually weak. And that is exactly what most bottles aim at: the healthy adult hoping for more energy, a sharper memory, better concentration or a brighter mood. Large, careful studies in healthy people usually find little to no measurable difference here. For the memory of healthy older adults: no demonstrable effect in the largest trials (Dangour et al., 2010, OPAL; Andrieu et al., 2017, MAPT). For the mood of people without depression: next to nothing (Deane et al., 2021, The British Journal of Psychiatry). With a real, diagnosed depression it is different – there, EPA-rich omega 3 as an add-on can indeed help (Liao et al., 2019, Translational Psychiatry). But that is a medical situation, and it belongs with your GP or psychiatrist.

Even for the heart the story is divided: a large, much-cited analysis found no effect on death, heart attack or stroke (Rizos et al., 2012, JAMA), while newer analyses see at most a modest benefit, strongest in people who are already ill (Hu et al., 2019, Journal of the American Heart Association; Siscovick et al., 2017, Circulation). The spectacular promises from the advert are therefore hard to find in the data.

The honest summary? Omega 3 is more like maintenance on a house than a renovation. You don’t feel it right away. Over the long term it may contribute to preservation, but it is not a switch that pumps out energy or focus.

Now the real omega alphabet: who is 6, who is 9, and who is 7?

Omega-6: the much-feared neighbour

Omega-6 revolves mainly around linoleic acid, found above all in vegetable oils: sunflower oil, corn oil, soybean oil, and in nuts and seeds. Like ALA, linoleic acid is an essential fatty acid, your body cannot make it itself, so it has to come from food.

Omega-6 has gained a bad image in recent years, often from the idea that it is “pro-inflammatory” and that a Western diet is thereby out of balance. Scientifically, that picture is too crude. A recent review shows that linoleic acid is in fact associated with a lower risk of cardiometabolic disease, and that it does not confirm the supposed “inflammation dogma”, in clinical studies linoleic acid lowers inflammatory markers rather than raising them (Belury, 2023, Current Opinion in Clinical Nutrition and Metabolic Care). An extensive review of soybean oil, the most-used vegetable oil worldwide, reaches the same conclusion: there is no good evidence that omega-6, or a high omega-6-to-omega-3 ratio, in itself causes inflammation or oxidative stress, and health authorities have consistently rejected the idea of an “ideal ratio”, the emphasis is on enough of each type of fat, not on a precise ratio (Messina, Shearer & Petersen, 2021, Nutrition).

So where is the real problem? Not that we eat too much omega-6. The problem is that most Western diets contain relatively little omega-3. The solution is therefore rarely “less omega-6”, but almost always “add more omega-3”.

Omega-9: the fatty acid you don’t strictly need and that is valuable anyway

Omega-9 revolves around oleic acid, the main component of olive oil. Here is a crucial difference from omega-3 and omega-6: oleic acid is not essential. Your body can simply make it itself from other fats. So there is, strictly speaking, no “deficiency” of omega-9 to worry about.

And yet oleic acid is not just a neutral filler. A large meta-analysis of 32 cohort studies with more than 840,000 participants found that a higher intake of monounsaturated fat, especially via olive oil specifically, is associated with less all-cause mortality, less cardiovascular death and fewer strokes. Strikingly: that benefit turned out to be tied above all to olive oil itself, and not simply to “monounsaturated fat” in general, whatever its source (Schwingshackl & Hoffmann, 2014, Lipids in Health and Disease). That fits the broader picture of the Mediterranean dietary pattern, in which olive oil plays a central role.

In short: you don’t need an omega-9 supplement. But olive oil on your plate is – quite apart from that “omega-9” framing – genuinely a sensible choice.

Without fish: what if I eat plant-based?

I’m adding this part because it isn’t fair for a story about omega to be only about fish. Anyone who eats vegetarian or vegan deserves the same sober, scientific answer, not a footnote.

The core is a biochemical fact I touched on above, but which becomes decisive here. There are two kinds of plant-based omega-3 sources, and they are not interchangeable with fish:

The raw material: ALA from flaxseed, chia seed, walnuts, hemp and rapeseed oil. This is alpha-linolenic acid, the plant-based omega-3. Your body can in principle make EPA and DHA from it, but the conversion is inefficient: reviews show that supplementing with ALA or ALA-rich oils usually does raise EPA levels a little, but has no measurable effect on DHA or on the omega-3 index (Takic et al., 2022, Molecules; Deckelbaum & Torrejon, 2012, Journal of Nutrition). In other words: a spoonful of flaxseed on your yoghurt is healthy and worthwhile, but biologically it is not the same as eating fish. It tops up the raw material, not automatically the end product.

The end product: DHA and EPA straight from algae. And here is the loveliest solution, one many people don’t know: algae oil skips the fish and goes straight to the original source. And it demonstrably works, a randomised study showed that algae-oil DHA is well absorbed and raised DHA levels in blood and tissue four- to fivefold (Lloyd-Still et al., 2006, Nutrition; studied in a specific patient group, but absorption itself is a general principle).

The honest conclusion for those who eat plant-based: don’t rely on flaxseed alone for your DHA. If you want to play it safe, algae oil is the scientifically most defensible route, the same fatty acids as in fish, but without the fish, without the mercury question, and with a smaller ecological footprint. For the precise choice and dosage in your situation, as always, your GP or a dietitian is best placed to look along with you.

The question I asked myself out loud one day: why don’t we just eat the algae?

Microalgae – tiny plants in the water – are the original makers of EPA and DHA in the ocean. Small fish eat those algae, bigger fish eat the small fish, and at the end of that chain stand we, with a fork.

And then I thought: but the fish is really a detour. A middleman. Why don’t we just take the source itself? Then surely I take the fresh version, without all the worries that come with fish, the mercury, and in the worst case bacteria or other sources of contamination?

Here my answer became, honestly, more sobering than I had hoped. It is not a biological problem, it is a matter of price, scale and habit. Growing algae at large scale currently costs more energy and is more expensive than catching fish, even though per unit of land it actually yields more (Deepika et al., 2026). And fish feels like food to most people, while algae oil feels like a pill, that is human habit, not science.

The only reason it is not yet standard on everyone’s plate lies in the wallet, not in biology.

Omega-7: the newcomer from the macadamia nut

The main omega-7 fatty acid is palmitoleic acid. Like omega-9, this too is a non-essential, monounsaturated fatty acid: your body makes it itself from palmitic acid, with the help of an enzyme called stearoyl-CoA desaturase (Cetin et al., 2024, Frontiers in Endocrinology). It is sometimes called a “lipohormone”, because it is released by fat tissue and appears to influence organs such as the liver and muscles at a distance.

A placebo-controlled study in people with chronic muscle and joint complaints found no effect at all of omega-7 supplements on inflammatory markers (Sasagawa, Boclair & Amieux, 2021, Nutrients). A small pilot study in patients with ulcerative colitis did see a favourable signal on inflammatory values (Bueno-Hernández et al., 2017, Minerva Gastroenterologica e Dietologica), but that study was small and not repeated. And a much-cited, positive study on omega-7 and cholesterol and inflammatory values (Bernstein, Roizen & Martinez, 2014, Journal of Clinical Lipidology) has since been formally retracted by the journal itself.

For omega-7, the current verdict is: interesting biology, a plausible story, but no solid foundation to buy a supplement for as a healthy adult.

What would I look at and which seals make a bottle truly “the best”?

There is no single magic stamp that guarantees everything, but there are a few independent standards that separate the wheat from the chaff. The three that matter in practice:

• IFOS (International Fish Oil Standards). This counts as the strictest, most transparent standard, with a 5-star system. IFOS tests per production batch for purity (heavy metals such as mercury and lead, plus PCBs and dioxins), for potency (is the promised EPA + DHA really in there?) and for freshness/oxidation. The special thing: the test results per batch can be viewed online.
• GOED (Global Organization for EPA and DHA Omega-3s). The global industry body that de facto sets the quality standard serious brands follow, including maximum oxidation values.
• USP (United States Pharmacopeia) Verified. Confirms that the supplement delivers the stated strength, is free of harmful contaminants, and is made according to good manufacturing standards.

The most important concrete number behind this is the TOTOX value (Total Oxidation value), a measure of how “fresh” or “rancid” the oil is. TOTOX combines the peroxide value (early oxidation) and the anisidine value (later oxidation) into a single figure. The internationally used limits (from GOED, CRN and IFOS) are: peroxide value under 5, anisidine value under 20, and TOTOX under 26 – the lower, the fresher.

Besides the seals, a few simple facts help just as much:

• Look at the actual EPA + DHA content, not at “1000 mg fish oil”. The two are not the same.
• Store cool and dark, and take it with a meal containing some fat — that helps absorption.
• When in doubt: look first at what is already on your plate (oily fish, 1–2 times a week, varied in kind; or algae oil if you eat plant-based), and only then at a jar.

How do I know if I have enough, the omega-3 index

There is a blood test that measures precisely what you cannot feel yourself: the omega-3 index. It measures the percentage of EPA + DHA in the membrane of your red blood cells, and thereby gives a picture of your intake over the past months, far more informative than simply asking how much fish someone eats.

Research across ten large cohort studies suggests that an index below 4% is associated with a higher risk of fatal heart disease, and that an index between 8 and 12% goes together with a considerably lower risk (Harris, Del Gobbo & Tintle, 2017, Atherosclerosis). In people who took a high dose of pure EPA (icosapent ethyl) in a large cardiovascular trial, the estimated index rose from around 5% to around 7% (Harris & Jackson, 2019, Journal of Clinical Lipidology). A low index also turns out to be associated with a higher neutrophil-to-lymphocyte ratio, a marker of low-grade inflammation (McBurney, Tintle & Harris, 2022, Prostaglandins, Leukotrienes and Essential Fatty Acids).

The question I was actually asking wrong

Along the way I noticed that my original question, “do I feel something?”, was perhaps the wrong one.

A better question is: “Does this demonstrably contribute to my health, given my situation?”

Those are two very different things. You never feel a smoke detector. A seatbelt feels like nothing. And yet they are valuable, precisely because they prevent problems you never consciously experience. Some healthy choices work in silence.

In closing

The omega alphabet is bigger than I thought when I first picked up a jar. Omega-6 is no enemy, most people already have plenty of it, though a fragile oil should not be overheated. Omega-9 is valuable via olive oil, but not an essential fatty acid to supplement separately. Omega-7 is an intriguing, still-young file with more promise than proof. And omega-3 remains, of this whole alphabet, the only fatty acid for which a deficiency is realistic for many people and the only one for which science consistently shows a measurable effect on triglycerides. Those who eat plant-based need not be left out: flaxseed provides the raw material, but algae oil provides – like fish – the real end product.

Not everything expensive is valuable. But everything that is valuable deserves to be examined honestly, including by me, even when the answer is more uncomfortable than the number on the label.

This article is not medical advice. If you have questions about your own triglyceride levels or about omega-3 supplementation in your situation, talk to your GP or a treating specialist.

---

Sources

• Andrieu, S., Guyonnet, S., Coley, N., Cantet, C., Bonnefoy, M., Bordes, S., Bories, L., Cufi, M.-N., Dantoine, T., Dartigues, J.-F., Desclaux, F., Gabelle, A., Gasnier, Y., Pesce, A., Sudres, K., Touchon, J., Robert, P., Rouaud, O., Legrand, P., … Vellas, B. (2017). Effect of long-term omega 3 polyunsaturated fatty acid supplementation with or without multidomain intervention on cognitive function in elderly adults with memory complaints (MAPT): A randomised, placebo-controlled trial. The Lancet Neurology, 16(5), 377–389. https://doi.org/10.1016/S1474-4422(17)30040-6
• Belury, M. A. (2023). Linoleic acid, an omega-6 fatty acid that reduces risk for cardiometabolic diseases: Premise, promise and practical implications. Current Opinion in Clinical Nutrition and Metabolic Care, 26(3), 288–292. https://doi.org/10.1097/MCO.0000000000000919
• Bernstein, A. M., Roizen, M. F., & Martinez, L. (2014). Purified palmitoleic acid for the reduction of high-sensitivity C-reactive protein and serum lipids: A double-blinded, randomized, placebo controlled study [Retracted publication]. Journal of Clinical Lipidology, 8(6), 612–617. https://doi.org/10.1016/j.jacl.2014.08.001
• Bueno-Hernández, N., Sixtos-Alonso, M. S., Milke García, M. del P., & Yamamoto-Furusho, J. K. (2017). Effect of cis-palmitoleic acid supplementation on inflammation and expression of HNF4γ, HNF4α and IL6 in patients with ulcerative colitis. Minerva Gastroenterologica e Dietologica, 63(3), 257–263. https://doi.org/10.23736/S1121-421X.17.02367-4
• Cetin, E., Pedersen, B., Porter, L. M., Adler, G. K., & Burak, M. F. (2024). Protocol for a randomized placebo-controlled clinical trial using pure palmitoleic acid to ameliorate insulin resistance and lipogenesis in overweight and obese subjects with prediabetes. Frontiers in Endocrinology, 14, Article 1306528. https://doi.org/10.3389/fendo.2023.1306528
• Dangour, A. D., Allen, E., Elbourne, D., Fasey, N., Fletcher, A. E., Hardy, P., Holder, G. E., Knight, R., Letley, L., Richards, M., & Uauy, R. (2010). Effect of 2-y n-3 long-chain polyunsaturated fatty acid supplementation on cognitive function in older people: A randomized, double-blind, controlled trial. The American Journal of Clinical Nutrition, 91(6), 1725–1732. https://doi.org/10.3945/ajcn.2009.29121
• Deane, K. H. O., Jimoh, O. F., Biswas, P., O’Brien, A., Hanson, S., Abdelhamid, A. S., Fox, C., & Hooper, L. (2021). Omega-3 and polyunsaturated fat for prevention of depression and anxiety symptoms: Systematic review and meta-analysis of randomised trials. The British Journal of Psychiatry, 218(3), 135–142. https://doi.org/10.1192/bjp.2019.234
• Deckelbaum, R. J., & Torrejon, C. (2012). The omega-3 fatty acid nutritional landscape: Health benefits and sources. The Journal of Nutrition, 142(3), 587S–591S. https://doi.org/10.3945/jn.111.148080
• Deepika, C., Hankamer, B., & Ross, I. L. (2026). Can microalgal omega-3 PUFA production systems remain viable as GM plant sources emerge? Bioresource Technology, 441, Article 133525. https://doi.org/10.1016/j.biortech.2025.133525
• Dighriri, I. M., Alsubaie, A. M., Hakami, F. M., Hamithi, D. M., Alshekh, M. M., Khobrani, F. A., Dalak, F. E., Hakami, A. A., Alsueaadi, E. H., Alsaawi, L. S., Alshammari, S. F., Alqahtani, A. S., Alawi, I. A., Aljuaid, A. A., & Tawhari, M. Q. (2022). Effects of omega-3 polyunsaturated fatty acids on brain functions: A systematic review. Cureus, 14(10), Article e30091. https://doi.org/10.7759/cureus.30091
• Festinger, L. (1957). A theory of cognitive dissonance. Stanford University Press.
• Harris, W. S., Del Gobbo, L., & Tintle, N. L. (2017). The Omega-3 Index and relative risk for coronary heart disease mortality: Estimation from 10 cohort studies. Atherosclerosis, 262, 51–54. https://doi.org/10.1016/j.atherosclerosis.2017.05.007
• Harris, W. S., & Jackson, K. H. (2019). Translating plasma eicosapentaenoic acid concentrations into erythrocyte percentages of eicosapentaenoic acid plus docosahexaenoic acid during treatment with icosapent ethyl. Journal of Clinical Lipidology, 13(5), 771–777. https://doi.org/10.1016/j.jacl.2019.07.001
• Hu, Y., Hu, F. B., & Manson, J. E. (2019). Marine omega-3 supplementation and cardiovascular disease: An updated meta-analysis of 13 randomized controlled trials involving 127 477 participants. Journal of the American Heart Association, 8(19), Article e013543. https://doi.org/10.1161/JAHA.119.013543
• Liao, Y., Xie, B., Zhang, H., He, Q., Guo, L., Subramanieapillai, M., Fan, B., Lu, C., & McIntyre, R. S. (2019). Efficacy of omega-3 PUFAs in depression: A meta-analysis. Translational Psychiatry, 9(1), Article 190. https://doi.org/10.1038/s41398-019-0515-5
• Lloyd-Still, J. D., Powers, C. A., Hoffman, D. R., Boyd-Trull, K., Lester, L. A., Benisek, D. C., & Arterburn, L. M. (2006). Bioavailability and safety of a high dose of docosahexaenoic acid triacylglycerol of algal origin in cystic fibrosis patients: A randomized, controlled study. Nutrition, 22(1), 36–46. https://doi.org/10.1016/j.nut.2005.05.006
• McBurney, M. I., Tintle, N. L., & Harris, W. S. (2022). The omega-3 index is inversely associated with the neutrophil-lymphocyte ratio in adults. Prostaglandins, Leukotrienes and Essential Fatty Acids, 177, Article 102397. https://doi.org/10.1016/j.plefa.2022.102397
• Messina, M., Shearer, G., & Petersen, K. (2021). Soybean oil lowers circulating cholesterol levels and coronary heart disease risk, and has no effect on markers of inflammation and oxidation. Nutrition, 89, Article 111343. https://doi.org/10.1016/j.nut.2021.111343
• Rizos, E. C., Ntzani, E. E., Bika, E., Kostapanos, M. S., & Elisaf, M. S. (2012). Association between omega-3 fatty acid supplementation and risk of major cardiovascular disease events: A systematic review and meta-analysis. JAMA, 308(10), 1024–1033. https://doi.org/10.1001/2012.jama.11374
• Sasagawa, M., Boclair, M. J., & Amieux, P. S. (2021). Omega-7 mixed fatty acid supplementation fails to reduce serum inflammatory biomarkers: A placebo-controlled, double-blind randomized crossover trial. Nutrients, 13(8), Article 2801. https://doi.org/10.3390/nu13082801
• Schwingshackl, L., & Hoffmann, G. (2014). Monounsaturated fatty acids, olive oil and health status: A systematic review and meta-analysis of cohort studies. Lipids in Health and Disease, 13, Article 154. https://doi.org/10.1186/1476-511X-13-154
• Siscovick, D. S., Barringer, T. A., Fretts, A. M., Wu, J. H. Y., Lichtenstein, A. H., Costello, R. B., Kris-Etherton, P. M., Jacobson, T. A., Engler, M. B., Alger, H. M., Appel, L. J., & Mozaffarian, D. (2017). Omega-3 polyunsaturated fatty acid (fish oil) supplementation and the prevention of clinical cardiovascular disease: A science advisory from the American Heart Association. Circulation, 135(15), e867–e884. https://doi.org/10.1161/CIR.0000000000000482
• Takic, M., Pokimica, B., Petrovic-Oggiano, G., & Popovic, T. (2022). Effects of dietary α-linolenic acid treatment and the efficiency of its conversion to eicosapentaenoic and docosahexaenoic acids in obesity and related diseases. Molecules, 27(14), Article 4471. https://doi.org/10.3390/molecules27144471
• Wang, T., Zhang, X., Zhou, N., Shen, Y., Li, B., Chen, B. E., & Li, X. (2023). Association between omega-3 fatty acid intake and dyslipidemia: A continuous dose-response meta-analysis of randomized controlled trials. Journal of the American Heart Association, 12(11), Article e029512. https://doi.org/10.1161/JAHA.123.029512
• Yang, B., Tseng, P.-T., Hu, X., Zeng, B.-Y., Chang, J. P.-C., Liu, Y., Chu, W.-J., Zhang, S.-S., Zhou, Z.-L., Chu, C.-S., Chang, C.-H., Tu, Y.-K., Wu, Y.-C., Stubbs, B., Carvalho, A. F., Lin, P.-Y., Matsuoka, Y. J., Suen, M.-W., & Su, K.-P. (2022). Comparative efficacy of omega-3 polyunsaturated fatty acids on major cardiovascular events: A network meta-analysis of randomized controlled trials. Progress in Lipid Research, 88, Article 101196. https://doi.org/10.1016/j.plipres.2022.101196
• Yang, B., Tseng, P.-T., Hu, X., Zeng, B.-Y., Chang, J. P.-C., Liu, Y., Chu, W.-J., Zhang, S.-S., Zhou, Z.-L., Chu, C.-S., Chang, C.-H., Tu, Y.-K., Wu, Y.-C., Stubbs, B., Carvalho, A. F., Lin, P.-Y., Matsuoka, Y. J., Suen, M.-W., & Su, K.-P. (2023). Corrigendum to “Comparative efficacy of omega-3 polyunsaturated fatty acids on major cardiovascular events: A network meta-analysis of randomized controlled trials”. Progress in Lipid Research, 89, Article 101206. https://doi.org/10.1016/j.plipres.2022.101206

Want to check something? The sources above point to the original publications. If you spot an error, do let me know.