Omega-3 is sold with more adjectives than almost anything in the supplement aisle, so it is worth starting from the one figure a European regulator has actually committed to.
EFSA sets an adequate intake of 250 mg per day of EPA plus DHA combined for adults. Separately it sets 0.5% of energy for alpha-linolenic acid, which is the plant omega-3 and a different thing. Those two numbers are the whole official position, and they are modest.
Three molecules, one label
The word “omega-3” covers fats that behave differently in the body.
ALA (alpha-linolenic acid) comes from flaxseed, rapeseed oil, walnuts and chia. It is an essential fatty acid, it has its own reference value, and the body can convert it to the long-chain forms — badly. Conversion to EPA is limited; conversion onward to DHA is very limited, and lower in men than in women.
EPA and DHA come from oily fish, and from the algae the fish get them from. These are the forms the 250 mg figure refers to, and the ones the cardiovascular and neural evidence concerns.
Which means a product advertising omega-3 on the front may be delivering a fat your body converts at single-digit efficiency, or the one it uses directly, and the front of the pack is not obliged to tell you which.
“Rich in omega-3” on a rapeseed spread and on a tin of sardines are two different statements sharing a phrase.
Reaching 250 mg
Two portions of oily fish a week gets an average adult there comfortably, which is why national advice tends to be phrased that way rather than in milligrams. The reliable species are unglamorous and cheap: mackerel, sardines, herring, anchovies, and farmed or wild salmon. Tinned counts. Tinned sardines are probably the best value-per-milligram on any shelf in Europe.
Tuna is the awkward one. Fresh tuna carries a reasonable amount; the canning process for most tinned tuna leaves it with far less, which is why tinned tuna is usually classed as a white fish for this purpose.
If you don’t eat fish
Algae oil is the direct answer — EPA and DHA from the original source, skipping the fish entirely. It is more expensive than fish oil and it is the only supplement that actually substitutes for the fish rather than for the plant precursor.
Flax, walnuts and rapeseed oil are worth eating for their own sake and will cover the ALA requirement easily. They will not reliably deliver the long-chain forms, and a diet that relies on conversion tends to land short on DHA in particular.
What the evidence supports, and what it doesn’t
The clearest and least contested case is dietary: populations eating oily fish regularly do better on cardiovascular outcomes, and health bodies across Europe recommend it. The evidence for supplementing omega-3 in people who already eat a reasonable diet is much weaker — large trials have repeatedly come back neutral for general prevention — and the gulf between “eat the fish” and “take the capsule” is one of the widest in nutrition.
High-dose prescription preparations for specific conditions such as very high triglycerides are a separate, medical question, and not one to self-prescribe from a supermarket shelf.
For a healthy adult the practical version is short. Two portions of oily fish a week. If that is not happening and is not going to, an algae or fish oil giving roughly 250 mg of combined EPA and DHA per day covers the reference intake for the price of a coffee a fortnight.
