Omega-3 and oily fish: what the NHS actually recommends
Before you buy a fish oil capsule, the UK advice is about food and it is specific: two portions of fish a week, one of them oily. Here is what counts, what a portion is, and the limits that apply to some groups.
Published 13 August 2026
Fish oil is one of the biggest-selling supplements in Britain. The official UK advice on omega-3 is not about capsules at all - it is about food, and it is unusually specific.
The recommendation
The NHS advises eating at least 2 portions of fish a week, including 1 portion of oily fish.
A portion is around 140g cooked.
That is the whole guidance. Two portions, one oily, roughly a palm-sized piece each.
What counts as oily
Herring, pilchards, salmon, sardines, sprats, trout and mackerel.
One thing catches people out constantly: fresh and canned tuna do not count as oily fish. Tuna is a perfectly good source of protein and it counts towards your two portions, but not towards the oily one.
Tinned sardines and mackerel are the cheapest way to hit this by a distance, and both keep in a cupboard indefinitely.
The limits, which apply to some people and not others
This is the part usually left out of supplement marketing, and it matters.
- Girls and women who may have children one day, or who are pregnant or breastfeeding: no more than 2 portions of oily fish a week, because certain pollutants can build up over time.
- Pregnant or breastfeeding: avoid shark, swordfish and marlin entirely. Limit tuna to no more than 4 cans or 2 steaks a week.
- Children under 16: avoid shark, swordfish and marlin, because of mercury.
Everyone else has no upper limit on oily fish beyond common sense.
Where supplements fit
If you eat oily fish regularly, a fish oil capsule is largely redundant. If you never eat fish - because you do not like it, or you are vegetarian or vegan - then it is a genuine and identifiable gap, and that is exactly the situation supplements exist for. Algae-derived omega-3 is the plant-based option.
The authorised wording is that EPA and DHA contribute to the normal function of the heart, at an intake of 250mg a day. DHA also contributes to the maintenance of normal brain function and normal vision, at the same intake. Those are the claims permitted on the GB Nutrition and Health Claims Register, and they are narrower than most fish oil packaging implies.
How to actually do it
Two portions a week sounds simple and most people still miss it, usually because fish is treated as a thing you cook rather than a thing you keep in.
- Tinned sardines on toast. Five minutes, and one of the cheapest oily portions available.
- A tin of mackerel through a salad or into pasta.
- A frozen salmon fillet in the oven with whatever else is going.
Frozen counts. Tinned counts. It does not have to be fresh from a fishmonger to meet the guidance.
The pattern here
This is the third UK recommendation in a row where the honest answer is food first and a supplement only for a specific, identifiable gap - the same as with fibre and magnesium. Vitamin D is the one genuine exception, because it is about British latitude rather than diet. We covered that in vitamin D in the UK.
Sources
NHS, Fish and shellfish. At least 2 portions of fish a week including 1 of oily fish; 140g portion; oily fish list; limits for specific groups.
General information, not medical advice. If you are pregnant, have a health condition or take prescription medication, speak to your GP or pharmacist.
