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Introduction
Let me guess, you think that we need to take fish oil to stay healthy. Well, that is another achievement of marketing. The reality is that EPA and DHA, the super-famous components of fish oil, are not essential at all. While you are reading this, your body is happily producing them. This article explains which are the real essential fatty acids that you must eat to stay healthy. For this, I followed the very interesting papers written by Ralph T. Holman (Ralph T. Holman, 1998) and Spector and Kim (Spector & Kim, 2015).
The story of the discovery
Back in 1930, George and Mildred Burr published a work describing that when rats eat meals without fats for weeks, they developed dermatitis, kidney degeneration and died early. As a result of their experiment, they concluded that linoleic acid, and most likely alpha-linolenic acid as well, were essential fatty acids for rats, this meaning that they either ate these particular fatty acids in their meals, or would develop disease and die soon (Burr & Burr, 1930).
It took time to establish that these two fatty acids are also essential for humans. The first clue came from a study lead by Arild Hansen and Hilda Wiese (Hansen et al., 1958). In the 1940s – 1950s, baby formula increasingly substituted breastfeeding in the US for a number of reasons (marketing was involved again). This baby formula was prepared with skimmed cow milk, which was low in fats. In parallel to the growth in popularity of baby formula, a high incidence of infant eczema developed (Holman, 1998). Hansen and colleagues found that this affection was resolved by adding linoleic acid to the baby formula (Hansen et al., 1958).
Now it was the turn to prove that the same applied to adults. However, it wasn’t until 1969, when a 78-year-old lady died from fat-free parenteral nutrition (PN), that the importance of ingesting essential fatty acids became clear (Holman, 1981). It seems the same mistake was commited: A lack of interest in including fats in nutrition. However, in this case they tried, but the difficulties of keeping fats dissolved in water prompted scientists to decide that they were good to go with fat-free PN. Parenteral nutrition is not the dripping thing that keeps us hydrated when we go to the hospital. It is a dark solution plenty of nutrients that is injected straight to the heart to keep alive patients whose digestive system is not working properly. Due to the fatal outcome of this lady, it became clear that linoleic acid is an essential fatty acid for adult humans as well.
What about the other essential fatty acid? Its name is alpha-linolenic acid, and it took a bit more time to establish its essentiality for human health. It was not until 1982 that a case report presented the evidence. This case was a 6-year-old girl who had to undergo surgery to remove 3 m of her intestine to save her life, as she accidentally self-infringed a rifle shot in the abdomen (Holman et al., 1982). The girl received total parenteral nutrition (TPN – total because scientists learned to include fats), but only linoleic acid. After a time, the girl experienced numbness, weakness, inability to walk and blurring of vision. These symptoms disappeared when alpha-linolenic acid was added to her TPN. At that time, scientists knew of the importance of DHA in vision, learning ability and wound healing. However, the girl recovered thanks to alpha-linolenic acid alone, and it was understood that her body subsequently converted alpha-linolenic acid in EPA, and then DHA to recover from her symptoms.
What do these essential fatty acids do?
They themselves are used by our body. In addition, they are the initial substrate that our body uses to produce fatty acids that are longer and have a higher degree of unsaturation. These longer and polyunsaturated fatty acids perform essential functions in human physiology.
Fatty acids are primarily synthesized as lineal, non-bendable molecules. However, if double bonds are introduced in the synthesis process, they bend. The more double bonds (unsaturations) are introduced, the more bending positions are caused. For example, if you open a matchbox, it is like opening a box of lineal (saturated) fatty acids, they look like straight sticks. This is why butter or lard, which are rich in lineal (saturated) fatty acids are solid at room temperature, because the fatty acids, or stick-like molecules, are highly ordered in space thanks to their shape. Unsaturated fatty acids don’t keep their position at room temperature, and this is why oils, which are rich in unsaturated fatty acids, remain disordered and therefore liquid at room temperature.
Cell membranes are composed of fatty acids as part of higher-order molecules named phospholipids. Depending on their function, cells will need a more or less rigid membrane, and this is achieved in part by the richness in saturated and unsaturated fatty acids of the phospholipids they place in their membranes. For instance, how weaving do you think neuron membranes need to be at their synaptic end? A lot, because at that place, little sacs need to be easily prepared to send neurotransmitters to the next neuron. Consequently, these membranes are highly populated with phospholipids bearing DHA (and other poly-unsaturated fatty acids such as arachidonic acid – ARA). On the other hand, membranes of neuronal axons are rich in saturated fatty acids because they have to behave as a more rigid insulation cover, like the plastic cover in an electric cable.
Moreover, EPA, DHA (and others) are used by our body to manufacture some molecules that act in many essential processes, such as inflammation release. Therefore, polyunsaturated fatty acids such as EPA, DHA or ARA perform very important functions, but they are not essential, as we produce them. Those that are essential are linoleic acid and alpha-linolenic acid, as if you don’t ingest it, you cannot produce EPA, DHA or ARA.
But we humans are very bad in producing DHA, this is why we need fish oil!
It is widely assumed that humans are very bad in converting the fatty acid precursor alpha-linolenic acid (ALA) into DHA, at around 1 % of ALA ingested. However, this low conversion rate comes from measurements of DHA in the blood, and the measuring technique has been challenged (Domenichiello et al., 2015). In any case, let’s put our deficient capacity of DHA production in context. Your healthy adult brain contains around 3.5 g of DHA (Lacombe et al., 2023), and it uptakes 4 mg of DHA per day from your blood to replace used DHA (Bazinet et al., 2022; Klievik et al., 2023; Rapoport et al., 2011). Your fat also contains DHA, around 20 – 30 g, which is released to the bloodstream in the form that the brain prefers to uptake, as a free fatty acid (Bazinet et al., 2022). From this data, the (healthy adult) brain does not need much DHA per day, just 0.1 % of its constant DHA pool, and our fat has plenty of stock provenient from the liver. Following this reasoning, this would suggest that reasonable variations in blood DHA between humans might be ok. This brings me to Dr R. Bazinet words: “I think the question was framed in the wrong way: It is not how much you can convert [to DHA], it is how much you need!” (Bazinet R et al., 2022).
Another fascinating discovery is that when we ingest capsules with fish oil, our liver slows down internal DHA production (Metherel et al., 2024). To me, this finding highlights how fine-tuned our “DHA system” is.
Dear vegans and vegetarians…
What follows is for you. Studies show that the DHA levels in your blood are likely lower than in omnivorous people; but not much lower (Burns-Whitmore et al., 2019; Sinclair et al., 2022). This demonstrates that your liver is converting ALA in DHA! Furthermore, your fat stores DHA likewise the fat of omnivorous people, but at a lower level (0.12 % of total fatty acids is DHA in the fat of lacto-ovo vegetarians vs 0.18 % in omnivores) (Miles et al., 2019). However, to keep these or higher levels of DHA in your body, it is your responsibility to ingest sufficient ALA-rich foods. You must be careful here, because most vegetal foods and oils will be richer in the other essential fatty acid: Alpha-linoleic acid (Hibbeln, Nieminen, Blasbalg, Riggs, & Lands, 2006). Therefore, please make sure you are ingesting ALA rich foods, such as flaxseed oil, flaxseeds, chia seeds, walnuts, and canola oil.
A second point to consider is your overall health, particularly relating to your liver. As your liver is the main DHA production hub, if you have a liver disease, your internal DHA production capacity might be compromised. If this is the case, you should seek medical advice (not google, not internet, not even this blog). If your doctor recommends you take DHA capsules due to liver disease, there are great DHA capsules sourced from microalgae commercially available. This would also apply if your genetic background is not very efficient in producing DHA. However, to find out about this, you should measure your DHA profile (there are a few companies doing this – I have nothing to do with them).
Finally, I want to emphasize here that the above applies only to healthy adults. Not to lactating women, nor to babies, children, adolescents, elderlies, adults with diseases, particularly liver disease. For them, much more care needs to be taken, and health services should be ready to help them.
Then, does it make sense to capture oily fish to produce fish oil, if EPA and DHA are not essential?
The industry of omega-3 fatty acids makes money disseminating the message that this oil is good for your cardiovascular health. However, as you could read above, this claim is inconclusive and under constant debate (Abdelhamid et al., 2020), as it is based on the heavy-publisized idea that adult humans are bad at synthesizing DHA. Upon my modest review of the scientific literature, the consumption of capsules of fish (or krill oil) can have benefits only in cognition (summarised in (Prado-Cabrero & Nolan, 2021)). However, this is an open topic. My advice here is that, in view of the pressure put on marine ecosystems by climate change, we should leave the anchovies where they are and take our runners and do some sports to get healthier, and consume sufficent amounts of ALA and LA (more ALA than LA).
But again, this advice is for people that have the capability to take their runners and go out. What about the elderlies? What about autistic and other neurodivergent children? They can be very restrictive in their diets (Hoffmann et al., 2025), and they may need to carefully supplement what they eat to stay as healthy as possible, including the essential fatty acids. From here, I encourage families to seek medical advice and to demand that their governments provide better public access to expert medical and nutritional guidance.
The two essential fatty acids are present in flaxseed, chia, canola or hemp oil, and the subsequent fatty acids EPA and DHA can be obtained from microalgae. The sustainable sources are there, but expert advice needs to be put in place to make good use of them.
References
Bazinet R, Harris B, & Jackson KH. (2022). OmegaMatters – Episode 21: Dr Richard Bazinet.
