Omega-3 ALA, EPA and DHA: what's the difference?

Omega-3 is a family of fats, not a single nutrient, and the three types you need to know about are ALA, EPA and DHA. The difference matters: two of them are what your body actually uses, and the third is mostly found in plant foods but is not nearly as beneficial.

what are ALA, EPA and DHA?

They're three fatty acids in the same family of omega-3s. The difference is how long their carbon chains are. [1]

ALA (alpha-linolenic acid) is the short-chain one and is commonly found in nuts and seeds. It's an essential fatty acid, which means your body can't build it and has to get it from food.

EPA (eicosapentaenoic acid) and DHA (docosahexaenoic acid) are the long-chain forms. These are the ones your body uses directly and are responsible for most of the benefits. DHA is a structural fat: it's concentrated in the brain and the retina, where it sits in cell membranes rather than being burned for energy.

where do ALA, EPA and DHA come from?

ALA comes from plants: flaxseed and flaxseed oil, chia, walnuts, rapeseed oil, and soya foods. [1]

EPA and DHA come from the sea. Oily fish is the richest dietary source, and shellfish contain a little too. [1][6]

But fish don't make omega-3. They accumulate it, because the EPA and DHA in the ocean originates in micro-algae and works its way up the food chain. [1] This matters, because it means algae is a direct source too.

can your body make EPA and DHA from ALA?

Some, but usually not enough.

Your body can convert ALA into EPA, and then on into DHA. The ALA-EPA conversion works reasonably well. The ALA-DHA conversion is very low to negligible. [4]

What that means in practice: if you rely on nuts and seeds for your omega-3, you might manage enough EPA through your body's conversion process, but you're unlikely to be getting enough DHA.

Both percentages are shares of the ALA you started with, not of the step before. [4]

The evidence behind that is consistent. Studies that gave people ALA and followed it through the blood found roughly a fifth of it becoming EPA in young women, and only a small fraction becoming DHA.

In the companion study in young men, there was no detectable DHA at all across three weeks. [3][2] Those tracked a single dose, though. The more useful test is what happens when people simply eat more ALA for weeks or months, and there the answer is consistent: EPA rises, and DHA barely moves. Reviews of that work find no reliable increase in blood DHA at any ALA intake. [8][9]

In addition to the already poor conversion, a diet high in omega-6 (as most modern diets are), competes for the same enzymes and slows the whole process by up to half again. [4]

One of the researchers behind those original studies put it plainly in a later review: ALA is "a limited source" of the long-chain omega-3s. [9]

In summary, that means that eating nuts and seeds, or taking flaxseed supplements isn't a reliable way of increasing your EPA and DHA levels.  

what does a tablespoon of flaxseed actually get you?

A tablespoon of flaxseed contains about 2.35 g of ALA. [7] On paper that's a lot of omega-3. Two things happen to it before your body can use any of it.

First it has to be ground. In a whole seed the oil is locked inside a hard coat, and whole flaxseed passes through you largely undigested. Grinding releases it, which is why ALA is far more available from milled seed or oil than from whole seeds. [7] A tablespoon of whole seeds sprinkled on porridge delivers a good deal less than you might think.

Then it has to convert, and only the first half of that works. Reviews of ordinary diets put ALA-to-EPA conversion at around 6%, which from 2.35 g is roughly 140 mg of EPA. [4] Considering that average adults should be aiming for 250 mg a day for EPA and DHA combined, one spoonful get you part of the way there.

There's no equivalent sum to do for DHA, because the conversion rate is very low to negligible. [8][9] You can't count on it being there at all.

A tablespoon of ground flaxseed counts towards your EPA, then. It won't get you DHA.

is flaxseed a waste of time?

No. ALA is an essential fatty acid in its own right: your body can't make it and needs it from food. It also has an agreed benefit of its own, at a higher intake than the EPA and DHA ones. At 2 g a day, ALA contributes to the maintenance of normal blood cholesterol levels, and a single tablespoon of ground flaxseed clears that on its own. [7]

Flaxseed, chia and walnuts are genuinely good foods, and the fibre and lignans in ground flaxseed are genuinely good for you.

What ALA won't do is raise your DHA significantly. 

how much EPA and DHA do you need a day?

At 250 mg of DHA a day, scientists agree that DHA contributes to the maintenance of normal brain function and of normal vision.

At 250 mg of EPA and DHA combined, they agree that EPA and DHA contribute to the normal function of the heart.

There may be other benefits too, but these are the ones that experts all agree on.

DHA is the real powerhouse of the omega-3 family, as it's such an important structural component of many cells in the body.

From food, the NHS recommends at least two portions of fish a week, one of them oily, and notes that most of us aren't eating that much. [6]

how much flaxseed do you need for 250 mg of EPA and DHA?

On the EPA side, it's manageable. At around 6% conversion you'd need roughly 4 g of ALA a day to end up with 250 mg of EPA, which across the usual plant sources looks like this. [10]

Flaxseed and chia can easily be incorporated into a breakfast. Rapeseed oil means drinking three tablespoons of the stuff, and edamame would take more than a kilo.

On the DHA side, the range runs from about 4% down to nothing. Take the generous end of it and 250 mg of DHA would need around 6 g of ALA a day, which is about three tablespoons of ground flaxseed. That's assuming the best case scenario, without factoring in genetics or diet. [2][4][8][9]

You have no practical way of knowing which end of that range you're on. That makes ALA an unreliable route to getting enough DHA.

To guarantee you're getting enough DHA and EPA reliably, you need a source that already contains it.

where can I get EPA and DHA?

Oily fish is the direct route: salmon, sardines, mackerel, herring, trout, pilchards. [6]

If you don't eat fish and don;t wish to take fish oil, algae oil is the perfect alternative. Algae is the original source of EPA and DHA and provides them already formed with no conversion required. Ours is vegan omega-3 DHA and EPA from algae.

Whatever you choose, read the label for milligrams of DHA and EPA per serving rather than a combined "total omega-3" figure. Total omega-3 can be almost entirely ALA.

the bottom line

ALA is the plant omega-3 and an essential nutrient in its own right. EPA and DHA are the long-chain forms your body uses directly, and they come from the sea, originally from algae.

Your body converts ALA to EPA at something like 6% on an ordinary diet. Conversion on to DHA is very low to negligible. So if you rely on nuts and seeds for your omega-3, you may manage enough EPA, but you're unlikely to be getting enough DHA.

If you eat oily fish twice a week, you're covered. If you don't, ALA won't get you there on its own, so check that whatever you take lists EPA and DHA on the label rather than just omega-3.

Algae oil is a clean, fish-free way of getting the important EPA and DHA fatty acids your body needs.