ALA, EPA and DHA: why flaxseed oil is not the omega-3 you need

You may know this moment. Someone asks how you cover your omega-3. You point at the dark bottle in the fridge. Flaxseed oil, a spoonful in your muesli every morning, plus walnuts. The label says, in large letters and quite correctly: rich in omega-3.

And then a lab report is in front of you, and your omega-3 index is low. Clearly low. That is almost never about discipline. It is because the word omega-3 refers to three different molecules, and your body treats them very differently.

Three molecules, one name, and that is where the misunderstanding starts

Omega-3 is not a substance, it is an address. The name only tells you that the first double bond sits three carbon atoms from the far end. Three different residents live at this address.

Four carbon atoms and three double bonds of difference sound like a detail. For biology they are not. Think of a hardware store. ALA is a length of timber, EPA and DHA are a finished window frame with fittings. Both are made of wood. If the frame is what you are missing, the stack of timber helps you only as far as your workshop can build from it.

Even the European food safety authority makes this separation: ALA counts as its own essential fatty acid, and for EPA plus DHA there is a separate intake value.

And now you know why two people can eat the same amount of omega-3 and still show completely different blood values.

The chain that thins out inside your body

The most common objection here is a fair one: the body can convert ALA. The pathway exists and it runs in the liver. The only question is how much arrives at the end. Picture a row of workshops: at two stations the same machine is standing, it has to be used twice, and the last station is not even in the same building.

And now you know why a spoonful of flaxseed oil moves more at the start of the chain than at its end.

What the tracer studies actually measured

Online you will find conversion rates between 21 percent and below 0.1 percent. That looks like a contradiction. But the studies are measuring different things.

And now you know why two serious sources can quote different percentages.

Why women convert differently, and what estrogen has to do with it

When two people eat the same and only one of them has a decent omega-3 index, that is not a measurement error. It is a pattern in the data. And there is one study on this that goes beyond mere observation.

A second piece fits with this: according to Burdge and Calder, women use a smaller share of ALA for beta-oxidation. I still stay careful. These data come from special groups on hormone therapy. Transferring them to the natural cycle is an interpretation, not a measured fact. More on this in the article on cycle based nutrition and on the blood sugar and hormone axis in women.

And now you know why a single blanket percentage for all people could never work.

Your enzyme is not yours alone: the linoleic acid competition

This part interests me most in clinical work. It is not about your omega-3 at all, but about what lies next to it on the plate.

Delta-6 desaturase, the bottleneck at station 1 and station 4, is not picky. It takes ALA from the omega-3 family and linoleic acid from the omega-6 family. Both stand at the same counter.

Linoleic acid is the most common polyunsaturated fatty acid in a western diet. Sunflower oil, safflower oil and many processed foods deliver it in amounts that never existed in evolutionary terms. The obvious conclusion would be: less omega-6, more conversion. That conclusion is too simple.

I would also warn against over-reading this. 3.6 percent more incorporation is real, but it is not a doubling, and the exit toward DHA stays practically closed. Anyone who changes their cooking oils does so for good reasons. It just does not answer the DHA question. More on this under fries or banana.

And now you know why it also matters how long the queue in front of your enzyme is.

Genes, ancestry and why some people do better with flaxseed oil

You may know someone who swears flaxseed oil changed something for them, while you feel nothing at all. Before you start doubting yourself: there is a biological explanation for this in the genome. The two enzymes are encoded by neighbouring genes, FADS1 for delta-5 desaturase and FADS2 for delta-6 desaturase.

A review article puts the genetically explained variance for arachidonic acid levels at 28.5 percent. That figure applies explicitly to the omega-6 branch, not to DHA. But it does show the order of magnitude: for a diet dependent blood value, that is a great deal.

A Swedish group studied 5652 people from five European cohorts and found two common FADS haplotypes that differ markedly in how well they build long chain fatty acids. The more efficient one arose after the lineages of modern humans and Neanderthals separated, and it shows signs of positive selection. So the ability to build long chain fatty acids from precursors is itself an adaptation. On current data, though, even the more efficient variant is not enough to cover the DHA requirement from flaxseed oil alone.

And there is one more level above this. A study of 144 human liver samples found allele specific DNA methylation between FADS1 and FADS2, clearly associated with FADS1 activity. So between your gene and your enzyme performance sits another layer of regulation. For me this is one of the most honest moments in this whole topic. That the effect is not just a snapshot is shown by a third piece of work: 122 men were followed for three years, and carriers of one particular variant ended up with lower levels of EPA and DPA.

And now you know why your neighbour's experience with flaxseed oil says little about you.

What EPA and DHA do in your body that ALA cannot

Up to here it has been about amounts, now it is about jobs. The question is not whether EPA and DHA are rarer than ALA, but whether they hold roles that ALA cannot take over.

DHA changes the physics of your cell envelopes

DHA with its six double bonds is a biophysical extreme case. A review describes what its incorporation into membrane phospholipids sets off: altered order of the acyl chains, altered fluidity, different permeability, different activity of membrane proteins. My metaphor for this: the difference between a rigid plastic window and one that can be opened. Membrane fluidity can co-determine how well receptors change their shape and how signals travel inward. Why this matters for fat metabolism is covered in the article on zone 2 training.

From EPA and DHA come the brakes on inflammation

This is the strongest functional difference between the three forms. An inflammation that is not actively brought to an end stays quietly in the background, a theme in the article on silent inflammation.

DHA sits where it is hardest to replace

In the retina, DHA is a main structural lipid of the outer segment membranes of the photoreceptors and can shape permeability, fluidity and thickness there, and according to a review on the retina it may thereby shape phototransduction itself. It is hard to make the difference between precursor and end product more concrete: if your body is to see, it needs DHA in the retinal membrane, not ALA in the blood.

And now you know why this is not about quantity, but about function.

Where EPA and DHA sensibly come from, and why fish size matters

If the conversion is narrow, two routes remain: small fatty fish such as sardine, anchovy, herring and mackerel, or microalgae oil. Here I part ways with many guides. I do not recommend large predatory fish, no salmon, no tuna, not even in organic quality. There is a physical reason for that.

An organic label says something about feed, husbandry and stocking density. It says nothing about how far up the food web an animal sits and how long it lived. Yet both determine the mercury burden. Small schooling fish therefore answer two questions at once: plenty of EPA and DHA at a low trophic level. The European authority also weighs the benefit and risk of eating fish species by species rather than judging across the board.

For everyone eating plant based: algae oil is not a fallback

It matters to me to say this without any undertone. Plant based eating has many well documented advantages. This article names one gap, and there is an equally plant based answer to it.

This was also tested directly: 32 adults received 600 mg DHA per day for two weeks, once from algae oil capsules and once from cooked salmon. DHA rose by about 80 percent in plasma phospholipids in both groups, with no significant difference. Transparency on this: the author group had ties to an algae oil manufacturer, but the same conclusion is supported by the independent Munich group.

The omega-3 index makes the question measurable

One blood value maps exactly this: the share of EPA plus DHA in the red blood cell membrane. It shows what has landed in your membranes, regardless of how much flaxseed oil you bought.

In a dose response study over five months, 115 adults received 0, 300, 600, 900 or 1800 mg EPA plus DHA per day. The index rose with the dose, and dose alone explained 68 percent of the variability. That is the contrast with ALA: with direct intake, the response is far more predictable. Everything on measurement methods and target ranges is in the article on the omega-3 index, and a broader overview of sources under omega-3 from plants, animals or algae.

And now you know why I ask about body length when it comes to fish, and not about the certificate.

What ALA can still do, and what the large heart trials show

Now it gets uncomfortable, and specifically for my own argument. This article moves on the level of molecules, enzymes and blood values. Whether more EPA and DHA leads to fewer heart attacks in the end is a different question. There the data are mixed.

Three large individual trials show how differently results can turn out, depending on dose, molecular form and baseline risk.

These findings cannot be fully reconciled. Differences in molecular form, comparator substance and baseline risk are being discussed. What matters to me is the safety signal: at very high doses, atrial fibrillation was observed more often in REDUCE-IT. So more is not automatically better, and the European authority has assessed the upper intake level in a dedicated opinion.

And now you know why I do not talk flaxseed oil down and still do not call it the omega-3 solution.

Frequently asked questions about ALA, EPA and DHA

Omega-3 in the bigger picture

The question of ALA, EPA and DHA hangs on three other topics: on measurement, on inflammation biology and on the toxicology of the food chain. From here, routes lead into those areas.