Anyone interested in omega-3 quickly ends up at fish oil within minutes. Salmon, mackerel, capsules with a fish symbol on the tin — the answer seems so obvious that the question behind it is hardly asked anymore.
And yet it is worth asking. Fish does not produce the fatty acids we eat it for itself. It absorbs them. And it absorbs them along with everything else that drifts through the sea.
This text explains which three fatty acids lie behind the umbrella term omega-3, how much the body needs of them each day, what actually becomes of plant-based omega-3 in the body — and why, in the end, the question of the source is more interesting than the question of the milligram amount.
First, the essentials in simple terms
"Omega-3" is not a single substance, but a collective name for three fatty acids. They differ in where they come from and what the body does with them. There is no need to know more at the start:
| Which one | Found in | What the body does with it |
|---|---|---|
| The plant-based one | Linseed oil, flaxseed, chia seeds, walnuts, rapeseed oil | It is the raw material. The body can use it to build the other two — but only poorly. |
| The one for heart and circulation | Microalgae. Through the food chain, it also ends up in fish. | The body uses it to make a range of its own messenger substances. |
| The one for brain and eyes | Microalgae. Through the food chain, it also ends up in fish. | It is a building material and sits firmly in the cell membranes of the brain and retina. |
From this follow the two sentences this text is about: The two important ones originally come from algae, not fish. And: From the plant-based type, the body can hardly make them itself. We’ll look at both in more detail shortly.
The three abbreviations on every package
The nutrition table does not contain descriptions, but abbreviations. There are exactly three, and they belong to the three lines above:
| Abbreviation | Stands for | This is |
|---|---|---|
| ALA | Alpha-linolenic acid | the plant-based one |
| EPA | Eicosapentaenoic acid | the one for heart and circulation |
| DHA | Docosahexaenoic acid | the one for brain and eyes |
From here on, the abbreviations are used in the text — exactly as they appear on the tin on the shelf. Once you can match them, you can read any nutrition table without help.
What the body really does with plant-based omega-3
The conversion of ALA to EPA and then to DHA happens through a chain of enzymatic steps. The first and slowest is handled by delta-6-desaturase — the same enzyme that also processes omega-6 fatty acids. So both fatty acid families compete for the same bottleneck, and in a typical Western diet omega-6 is far ahead in quantity. The final step to DHA also runs through a detour via another part of the cell — and is once again much less efficient.
In numbers, it looks like this:
| Conversion | Approximate amount |
|---|---|
| ALA → EPA | about 5 to 8 percent, and generally higher in women of childbearing age |
| ALA → DHA | usually under 1 percent, and in some studies barely measurable |
So the bottleneck is not EPA, but DHA. What this means in everyday life becomes clear when you translate the calculation into tablespoons.
What this means in tablespoons
For EPA, it still looks manageable: to reach around 250 milligrams of EPA through conversion, you need roughly three to five grams of ALA per day. That is about one teaspoon of linseed oil — realistic, if you think about it.
For DHA, the calculation falls apart. At a conversion rate in the region of half a percent, about 50 grams of ALA would be needed to obtain 250 milligrams of DHA — every day. Linseed oil contains about 53 percent ALA, which corresponds to around 95 grams of oil, or about seven tablespoons. Every day. That would also add up to about 850 kilocalories from this oil alone.
This is not a nutrition recommendation, but a ratio. It explains why flaxseed oil, chia and walnuts are excellent foods — and why they still do not cover DHA needs. If you want DHA, you have to take it in, not have the body make it for you.
Where fish gets its omega-3 from
This is where it gets interesting. The same also applies to fish. Salmon, herring and mackerel do not produce EPA and DHA in any meaningful amount themselves. They absorb them through their food.
At the start of this chain are microalgae. They are the true producers of the long-chain omega-3 fatty acids in the sea. Tiny plankton eat the algae, small fish eat the plankton, larger fish eat the small ones. With each step, the DHA moves further up — and eventually ends up on the plate.
Fish oil is therefore not the source of omega-3. It is a stopover. The fatty acid in salmon is the same fatty acid an alga formed weeks earlier.
What else comes along the way through the food chain
A food chain does not transport nutrients alone. Fat-soluble pollutants accumulate along the same route, and with each step they become more concentrated — the principle is called biomagnification. Three groups are especially relevant:
- Methylmercury enters seawater through industry and natural processes and binds to muscle tissue. Large, long-lived predatory fish at the end of the chain carry the highest amounts.
- Dioxins and dioxin-like PCBs are fat-soluble and therefore accumulate in fatty tissue — exactly where the oil is.
- Microplastics and the additives bound to them are the newest addition to this list and have not yet been fully assessed.
Good fish oil is purified, usually by molecular distillation, and reputable manufacturers have the limits tested. The point is not that fish oil is dangerous. The point is that purification is needed at all — because the oil comes from the middle of a food chain rather than from its beginning.
Algae oil: the direct route
Algae oil skips the chain. It is obtained from microalgae, usually from the genus Schizochytrium, which are cultivated in closed containers on a nutrient medium — comparable to the production of yeast or yogurt cultures. The algae grow there under controlled conditions and have no contact with the open sea.
That has three consequences that can be stated plainly:
- No accumulation from the marine food chain. What never was in the sea cannot absorb anything there.
- No fishing. The vast majority of fish oil produced worldwide comes from wild-caught small schooling fish such as anchoveta, sardines and anchovies — species that play an important role in the ecosystem as forage fish.
- No fish taste.The typical taste and burping after fish oil capsules are mainly caused by oxidation products. Algae oil is produced without a smell.
The remaining question is whether the body handles one oil differently from the other. It does not: the DHA molecules are identical, regardless of whether they come from a cultivated alga or from an alga that first passed through a fish. Absorption studies accordingly show that DHA from algae oil appears in the blood just as DHA from fish oil does.
Algae oil and fish oil in direct comparison
| Algae oil | Fish oil | |
|---|---|---|
| Position in the chain | Source — the alga produces EPA and DHA itself | Stopover — the fish absorbs both |
| Origin | Cultivated in closed containers | Wild-caught, mostly small schooling fish |
| Pollutants from the sea | No contact with the marine food chain | Purification necessary, usually molecular distillation |
| Fatty acid profile | Usually DHA-dominant | Usually EPA-dominant |
| Taste | Neutral | Fishy as soon as oxidation starts |
| For vegans | Suitable | Not suitable |
| Fish allergy | No fish protein included | Not suitable for affected individuals |
For fairness, one point should be added: the fatty acid profiles differ. Classic fish oils usually provide more EPA than DHA, while many algae oils are the other way around. Anyone specifically looking for a high EPA amount should therefore look at the label rather than the source — and anyone wanting both will find them in algae oils that list both fatty acids.
What EPA and DHA do in the body
For omega-3 — unlike most plant substances — there are well-supported, verified claims. They are tied to a daily amount, and that amount is the real benchmark when comparing products:
| Fatty acid | Claim | From what daily amount |
|---|---|---|
| EPA and DHA | contribute to normal heart function | 250 mg EPA and DHA |
| DHA | contributes to the maintenance of normal brain function | 250 mg DHA |
| DHA | contributes to the maintenance of normal vision | 250 mg DHA |
| EPA and DHA | contribute to the maintenance of normal blood triglyceride levels | 2 g EPA and DHA |
| EPA and DHA | contribute to the maintenance of normal blood pressure | 3 g EPA and DHA |
| ALA | contributes to the maintenance of normal blood cholesterol levels | 2 g ALA |
For pregnant and breastfeeding women, there is an additional claim: maternal DHA intake contributes to the normal development of the brain and eyes of the fetus and breastfed infant. The amount for this is 200 milligrams of DHA in addition to the general recommendation.
The table shows two things. First, the threshold for most claims is 250 milligrams per day — that is the number that matters. Second, it says EPA and DHA, not fish oil and not algae oil. The claim belongs to the fatty acid, not to its source.
How much per day — and how to tell if you’re deficient
As a guideline for adults, 250 milligrams of EPA and DHA together per day is recommended. Pregnant and breastfeeding women need an additional 200 milligrams of DHA. These amounts can be achieved through diet: two portions of fish per week, one of them fatty, cover them on average.
The word average carries a lot of weight here. Anyone who does not eat fish — for taste, conviction or because of an allergy — will practically not reach this amount through diet, because plant foods provide ALA and the conversion to DHA, as calculated above, does not hold up.
There is no simple self-test for a deficiency. Complaints such as dry skin, dry eyes or difficulty concentrating are often associated with it, but they have many possible causes and are not proof. Anyone who wants to know for sure can have the omega-3 index measured — it measures the proportion of EPA and DHA in the membranes of red blood cells and is therefore a long-term value over about three months. If symptoms persist, medical evaluation should come first, not capsules.
Where omega-3 is found in foods
| Food | Which fatty acid | Approximate amount per 100 g |
|---|---|---|
| Salmon, herring, mackerel | EPA and DHA | about 1.5 to 3 g |
| Sardines, anchovies | EPA and DHA | about 1.5 to 2 g |
| Linseed oil | ALA | about 53 g |
| Flaxseed, ground | ALA | about 20 g |
| Chia seeds | ALA | about 18 g |
| Walnuts | ALA | about 9 g |
| Rapeseed oil | ALA | about 9 g |
Two practical notes: flaxseed must be ground, otherwise it passes through the intestine largely unchanged. And linseed oil should be used cold and kept in the refrigerator — it oxidizes quickly, and oxidized oil not only tastes rancid, it also loses its purpose.
How to recognize a good supplement
The selection is confusing, but the criteria are manageable:
1. EPA and DHA instead of oil amount
On many packs, the amount of oil is printed in large type — for example "1000 mg". That is the capsule fill, not the omega-3 content. What matters is how much EPA and DHA are actually in it. That number is listed in the nutrition table, and only that can be compared with the 250 milligrams.
2. Protection against oxidation
Long-chain fatty acids are sensitive. A good supplement contains antioxidants such as rosemary extract, mixed tocopherols or ascorbyl palmitate and comes in light-protected glass rather than clear plastic. The TOTOX value has become established as a freshness indicator; in the industry, a value up to 26 is considered acceptable.
3. Traceable origin
For algae oil, that means: which algae, cultivated or harvested. For fish oil: which species, which fishing area, which purification method. If neither is stated, there is usually a reason.
4. What else is in the capsule
Some supplements combine omega-3 with vitamin D — useful, because both are fat-soluble and are absorbed together with a meal. Vitamin D contributes, among other things, to normal immune system function and the maintenance of normal bones.
Taking it: when and how
Omega-3 is fat-soluble and is therefore taken with a meal that contains some fat itself. Whether this happens in the morning or evening has no proven effect — what matters is consistency, because the amount in the cell membranes builds up over weeks. Anyone expecting a change should think in months, not days.
The recommended intake on the package should be followed. Anyone taking anticoagulant medication or facing surgery should discuss taking higher amounts with a doctor beforehand: EPA and DHA can affect blood clotting. The same applies in the case of existing conditions and during pregnancy — omega-3 is not the problem there, but coordination is part of it.
How well omega-3 is tolerated
In usual amounts, omega-3 is well tolerated. What may occur:
- Burping and aftertaste — common with fish oil, usually a sign of beginning oxidation. With algae oil, the fish taste is absent.
- Gastrointestinal discomfort such as soft stools or fullness, especially with larger single doses on an empty stomach.
- Longer bleeding time at high amounts — the reason for checking before operations.
The European Food Safety Authority has assessed additional intake of up to 5 grams of EPA and DHA per day as safe. Typical supplements are well below that.
Briefly summarized
- Omega-3 includes three fatty acids: ALA from plants, and EPA and DHA, which originally come from microalgae.
- The body can convert ALA, but poorly: about 5 to 8 percent becomes EPA, and under 1 percent becomes DHA. Linseed oil alone cannot cover DHA needs.
- Fish do not produce EPA and DHA themselves — they absorb both through microalgae. Fish oil therefore sits in the middle of the food chain, algae oil at its beginning.
- Along the same route, methylmercury, dioxins and PCBs accumulate. Fish oil therefore has to be purified; cultivated microalgae have no contact with the open sea.
- The fatty acids themselves are identical. DHA from algae oil reaches the body just as well as DHA from fish oil.
- 250 milligrams of EPA and DHA per day is the reference value against which supplements can be measured — not the amount of oil in the capsule.
Dietary supplements are no substitute for a varied diet and a healthy lifestyle.
