Omega 3 & Omega Oil Supplements: Types, Differences & How to Choose

Omega oils are one of the hardest supplement categories to compare at a glance. Fish oil, algae oil, cod liver oil, krill oil, evening primrose oil and blended plant oils all sit under the same "omega" heading, yet they come from completely different sources, supply different fatty acids, and are labelled in different ways.

The confusing part isn't whether omega oils are worth considering. It's that two products can both say "1000mg" on the front and provide very different amounts of the fatty acids that actually matter. A 1000mg fish oil capsule with 30% EPA/DHA is not the same as a 1000mg capsule with 55% EPA/DHA, even though the headline number looks identical.

This guide explains what to check when comparing omega oil supplements, including the difference between omega-3, omega-6, omega-7 and omega-9, why the percentage on the label matters more than the total oil weight, and how source, format and strength affect which product is right for your routine.

What are omega oils?

Omega oils are a group of polyunsaturated and monounsaturated fats, most commonly supplied as omega-3, omega-6, omega-7 and omega-9. The best-researched fatty acids in this category are EPA (eicosapentaenoic acid) and DHA (docosahexaenoic acid), both types of omega-3 found mainly in oily fish and marine sources.

EPA and DHA contribute to the normal function of the heart, and DHA contributes to the maintenance of normal brain function and normal vision, at an intake of 250mg per day. These are recognised nutritional roles under the GB Nutrition and Health Claims Register, not medical claims — a supplement does not diagnose, treat or prevent any condition.

"Omega oils" is a broad label, not one ingredient. Fish oil, algal DHA and cold-pressed seed oil all sit in the same category while providing very different fatty acid profiles.

Omega-3, 6, 7 and 9: what's the difference?

Products across this category aren't interchangeable, because each omega type behaves differently and comes from different sources.

• Omega-3 — the most researched group, supplying EPA and DHA (mainly from fish, krill and algae) and ALA (mainly from plant oils such as flaxseed). Most shoppers in this category are looking for omega-3, usually because oily fish intake is below the recommended two portions a week.
• Omega-6 — found abundantly in vegetable oils, nuts and seeds, so most people already get enough through diet. Evening primrose and starflower oil are the most commonly supplemented sources, supplying gamma-linolenic acid (GLA).
• Omega-7 — a less widely known fatty acid, supplied mainly through sea buckthorn oil and usually sold as a standalone specialist supplement.
• Omega-9 — found naturally in olive oil and avocados. It isn't classed as essential, since the body can produce it itself, and typically appears as one component within a blended oil rather than a standalone supplement.

Blended products such as flaxseed oil or "3-6-9" formulas supply more than one omega type per serving — useful for general dietary support, but less concentrated in any single fatty acid than a dedicated fish oil or algae oil supplement.

Total oil weight vs actual EPA & DHA content: what the percentage means

This is the single most useful thing to understand when comparing omega-3 products, and it's the reason two "1000mg" capsules can be very different supplements.

When a product states "1000mg fish oil (30% DHA/EPA)", the 1000mg refers to the total weight of the oil in the capsule. The 30% tells you how much of that oil is the fatty acids you're actually looking for. On that basis, a single capsule supplies in the region of 300mg combined EPA and DHA — not 1000mg.

Compare that with Lindens Omega 3 Fish Oil Extra (55% DHA/EPA) 1000mg, from the same manufacturer. It's also a 1000mg fish oil capsule, but the label states a higher 55% concentration, and the product itself confirms that two capsules provide 1100mg of combined omega-3 DHA and EPA.

Both products are described as "1000mg" fish oil. Neither figure is wrong — but comparing the 1000mg headline number alone tells you almost nothing about how much EPA and DHA you're actually getting. The percentage, and the manufacturer's own stated EPA/DHA figure where given, are what make the comparison meaningful.

Practical takeaway: when comparing fish oil products, look past the total oil weight and find the EPA/DHA percentage or the combined EPA+DHA milligram figure, usually shown in the nutritional information or supplement facts panel.

How to compare omega oil supplements

Once you know which figures to look for, comparing products across this category becomes far more manageable.

• Omega type — confirm whether the product is omega-3, 6, 7, 9, or a blend, since they aren't interchangeable.
• EPA/DHA concentration — for fish, krill and algae oil, check the percentage or the stated combined EPA+DHA amount rather than the total oil weight.
• Serving size — check whether the stated amount comes from one capsule, two capsules, or a measured liquid dose.
• Source — fish, algae, krill, cod liver oil, or a plant-based blend such as flaxseed or evening primrose oil.
• Single-source vs blended — a dedicated fish oil or algae oil supplement versus a multi-oil formula covering several omega types at once.
• Format — capsule, softgel or liquid, and whether it needs refrigeration.
• Additional ingredients — some products combine omega-3 with vitamin D, glucosamine or other nutrients.
• Dietary suitability — vegan and vegetarian shoppers need an algae or plant-based source rather than fish or krill oil.
• Number of servings — don't assume a bigger bottle or higher capsule count necessarily lasts longer once serving size is accounted for.

Real examples from our range

Three real products show how strength, source and format can differ within the same broad category.

Laid out together, these three products show why "omega oil" can't be judged as one product type: a high-concentration fish oil capsule, a fish-free algae capsule, and a refrigerated liquid plant-oil blend are built, sourced and taken very differently, even though all three sit in the same collection.

Fish oil, algae oil and plant oils: does the source matter?

Source affects both what a product provides and who it suits.

• Fish oil — the most widely available EPA/DHA source, typically from oily fish such as anchovy, sardine or mackerel. Not suitable for vegans or vegetarians.
• Cod liver oil — a fish oil that also naturally contains vitamin A and vitamin D, which changes who it's suitable for — see the safety section below.
• Krill oil — sourced from small crustaceans and not suitable for anyone with a shellfish allergy.
• Algae oil — EPA and DHA extracted directly from algae, the source fish get their own omega-3 from. It's the main way vegans and vegetarians can supplement EPA and DHA specifically, rather than relying on ALA alone.
• Plant oils (flaxseed, evening primrose, starflower, sea buckthorn) — supply omega-3 as ALA, omega-6 or omega-7 rather than EPA/DHA. ALA is not the same fatty acid as EPA or DHA and shouldn't be assumed to provide an equivalent amount of either.

If EPA and DHA specifically are what you're after, check the source: fish, krill and algae oil supply them directly, while most plant oils do not. Browse our fish oil range or full omega oils collection to compare sources side by side.

Capsules, softgels and liquids

Format is a practical rather than a medical consideration, but it affects which product fits your routine.

• Softgel capsules — the most common format for fish, krill and algae oil; a fixed, pre-measured serving, easy to store at room temperature.
• Liquid oils — usually taken by the spoonful; can suit people who prefer not to swallow capsules, but often need refrigeration and have a shorter shelf life once opened.
• Blended multi-oil formulas — available in both capsule and liquid form, typically combining several plant oils rather than a single concentrated fatty acid.

Format can also change storage requirements, so check both alongside the fatty acid content rather than choosing on format alone.

How much omega-3 do you need?

The NHS recommends eating at least two portions of fish a week, including one portion of oily fish, as the main dietary route to omega-3. Not everyone manages this consistently, which is one reason fish, algae and other omega-3 supplements are widely used.

For reference, the GB Nutrition and Health Claims Register sets out the intake levels tied to specific authorised claims: 250mg combined EPA and DHA per day for the heart-function claim, and 250mg DHA per day for the brain-function and vision claims. These are labelling reference points, not personalised dosing advice — your overall intake also includes omega-3 obtained through diet.

Always follow the serving recommended on the individual product rather than assuming a higher milligram figure means you should take more. If you're unsure how a supplement fits alongside your diet, a pharmacist or GP can advise on your individual circumstances.

Safety and suitability

Omega oil supplements are food supplements, not medicines, and shouldn't be used to diagnose, treat, prevent or cure disease. Supplements are intended to complement a balanced, varied diet, not replace it.

A few practical points worth checking on the label:

• Allergen information — fish oil and krill oil are unsuitable for people with a fish or shellfish allergy respectively.
• Dietary suitability — only algae oil and plant-based oils are suitable for vegans; fish, cod liver and krill oil are not.
• Vitamin A content — relevant specifically to cod liver oil and other fish liver oil products, as set out above.
• Storage — some liquid oils need refrigeration to stay fresh; always follow the instructions on the individual product.

Related concepts

• ALA vs EPA/DHA — ALA is a plant-based omega-3 found in flaxseed and similar oils; EPA and DHA are the marine-sourced omega-3s linked to the authorised heart, brain and vision claims. They are related but not interchangeable, and this distinction could support its own dedicated comparison article.
• Omega-3 vs omega-6 balance — most UK diets already provide ample omega-6 through cooking oils, while omega-3 intake is more commonly the gap worth addressing through diet or supplementation.
• Fish oil vs cod liver oil — both are fish-derived, but cod liver oil additionally supplies vitamin A and vitamin D, which changes who it's suitable for, as covered in the safety section above.
• Omega oils vs vitamin D — some combination products pair omega-3 with vitamin D; if you're specifically comparing vitamin D products, our Vitamin D supplements guide covers forms and strengths in more depth.

The practical takeaway

The omega oils category stops being confusing once you stop comparing products on the total milligram figure alone. The questions worth asking are:

• Which omega type does the product actually supply — 3, 6, 7, 9, or a blend?
• What percentage or milligram amount of EPA and DHA does it provide, not just the total oil weight?
• What's the source — fish, algae, krill, cod liver oil or a plant blend?
• How many capsules, or how much liquid, make one serving?
• Does the format and storage suit your routine?
• Does it meet your dietary or allergen requirements?

Compared on those terms, a 1000mg fish oil capsule, an algae-based vegan capsule and a refrigerated liquid blend stop looking like variations on the same product and start looking like what they are: genuinely different ways of getting essential fatty acids into your diet.

Sources & further reading

• NHS — Fish and shellfish nutrition
• GOV.UK — Great Britain Nutrition and Health Claims (NHC) Register
• ASA / CAP Code — Section 15: Food, food supplements and associated health or nutrition claims

Written by the Health Plus Living editorial team. Last reviewed: September 2026.