Omega-3 vs Fish Oil: What's the Difference and Which Should You Take?

Walk into any pharmacy or health food shop in the UK and you'll find shelves lined with both "omega-3" and "fish oil" supplements. Many people use these terms interchangeably, but they are not the same thing — and understanding the difference can significantly affect the quality and effectiveness of the supplement you choose.

In this article, we clarify the relationship between omega-3 and fish oil, explain what to look for on a label, and help you make an informed decision about which supplement is right for your health goals.

What Are Omega-3 Fatty Acids?

Omega-3 fatty acids are a family of polyunsaturated fats that are essential for human health. The term "essential" has a specific meaning in nutrition: the body cannot synthesise these fats on its own, so they must be obtained through diet or supplementation [1].

There are three main types of omega-3 fatty acids relevant to human health:

• ALA (Alpha-linolenic acid) — found in plant sources such as flaxseed, chia seeds, and walnuts. ALA is the most common dietary omega-3 but must be converted by the body into EPA and DHA to be biologically active — a process that is highly inefficient in humans [2].
• EPA (Eicosapentaenoic acid) — a long-chain omega-3 found primarily in marine sources. EPA has well-documented anti-inflammatory effects and plays a key role in cardiovascular and mental health [3].
• DHA (Docosahexaenoic acid) — a long-chain omega-3 also found in marine sources. DHA is a structural component of brain cell membranes, the retina, and the nervous system, and is critical for cognitive function throughout life [4].

EPA and DHA are the forms of omega-3 that deliver the majority of the health benefits associated with omega-3 supplementation.

What is Fish Oil?

Fish oil is a dietary supplement derived from the tissues of oily fish such as mackerel, sardines, anchovies, herring, and salmon. It is one of the richest natural sources of EPA and DHA — the two long-chain omega-3 fatty acids with the strongest evidence base for human health [5].

So the relationship is this: fish oil is a source of omega-3s, but not all omega-3 supplements are fish oil. Omega-3 supplements can also be derived from algae (algal oil), krill, or plant sources — each with different EPA and DHA content and bioavailability profiles. Browse our full range of fish oil & omega-3 supplements.

Fish Oil vs Algal Omega-3: What's the Difference?

For those who are vegan or vegetarian, algal oil is the primary alternative to fish oil as a source of EPA and DHA. Algal oil is derived from the microalgae that fish themselves consume — making it the original source of marine omega-3s in the food chain.

Research has shown that algal DHA is bioequivalent to DHA from fish oil [6], and some algal oils now also provide EPA. Algal omega-3 is also free from the risk of heavy metal contamination associated with some fish-derived products, and is more sustainable from an environmental perspective [7].

For non-vegans, high-quality fish oil remains the most widely studied and cost-effective source of EPA and DHA.

What Does the Research Say About Omega-3 and Fish Oil?

The health benefits of EPA and DHA from fish oil are among the most extensively researched in nutritional science:

Cardiovascular health: A large meta-analysis published in the Journal of the American College of Cardiology found that omega-3 supplementation significantly reduced triglyceride levels, a key cardiovascular risk factor [8]. The REDUCE-IT trial, published in the New England Journal of Medicine, found that high-dose EPA supplementation reduced major cardiovascular events by 25% in high-risk patients [9].

Brain and cognitive function: DHA is the predominant structural fatty acid in the brain, comprising approximately 97% of all omega-3 fatty acids in the brain [4]. Studies have associated higher DHA intake with reduced risk of age-related cognitive decline and improved memory function [10].

Inflammation and joint health: EPA and DHA inhibit the production of pro-inflammatory eicosanoids and cytokines. Clinical trials have demonstrated reductions in joint pain and stiffness in patients with rheumatoid arthritis following omega-3 supplementation [11]. See our joint & bone support collection for complementary supplements.

Mental health: A meta-analysis in Translational Psychiatry found that omega-3 supplementation — particularly EPA-dominant formulas — had a significant positive effect on depressive symptoms [12].

Eye health: DHA is a major structural component of the retina. Adequate DHA intake is associated with reduced risk of age-related macular degeneration [13].

How Much EPA and DHA Do You Need?

Most health authorities recommend a minimum of 250–500mg of combined EPA and DHA per day for general health maintenance in adults [14]. Higher doses of 1,000–4,000mg per day are used in clinical settings for specific conditions such as elevated triglycerides or inflammatory conditions, under medical supervision.

Crucially, when evaluating a fish oil supplement, look at the EPA and DHA content specifically — not just the total fish oil dose. A 1,000mg fish oil capsule may contain as little as 300mg of combined EPA and DHA, depending on the concentration of the product. Higher-concentration formulas provide more EPA and DHA per capsule and are generally better value.

What to Look for When Buying a Fish Oil Supplement

When choosing a fish oil or omega-3 supplement, consider the following:

• EPA and DHA content — check the label for the specific amounts of each, not just total fish oil
• Triglyceride vs ethyl ester form — fish oil in triglyceride form is better absorbed than the ethyl ester form [15]
• Purity and testing — look for products that are tested for heavy metals, PCBs, and dioxins
• Freshness — oxidised fish oil is less effective and can have an unpleasant taste; look for products with added antioxidants such as Vitamin E
• Sustainability — choose products sourced from sustainably managed fisheries, ideally with MSC certification
• UK manufacturing — products manufactured in the UK to GMP standards offer greater quality assurance

The Bottom Line

Omega-3 and fish oil are related but not identical terms. Fish oil is one of the best dietary sources of EPA and DHA — the long-chain omega-3 fatty acids responsible for the majority of health benefits associated with omega-3 supplementation. When choosing a supplement, prioritise the EPA and DHA content over the total fish oil dose, and look for a high-quality, pure, and sustainably sourced product.

For vegans and vegetarians, algal oil provides a bioequivalent source of DHA and increasingly EPA, without the need for fish-derived ingredients. Browse our fish oil & omega-3 range, or if you're over 50, see our guide to Best Supplements for Over 50s.

References

1. Simopoulos AP. The importance of the ratio of omega-6/omega-3 essential fatty acids. Biomedicine & Pharmacotherapy. 2002;56(8):365-379.
2. Burdge GC, Calder PC. Conversion of alpha-linolenic acid to longer-chain polyunsaturated fatty acids in human adults. Reproduction Nutrition Development. 2005;45(5):581-597.
3. Calder PC. Omega-3 fatty acids and inflammatory processes. Nutrients. 2010;2(3):355-374.
4. Innis SM. Dietary omega-3 fatty acids and the developing brain. Brain Research. 2008;1237:35-43.
5. Mozaffarian D, Wu JH. Omega-3 fatty acids and cardiovascular disease. Journal of the American College of Cardiology. 2011;58(20):2047-2067.
6. Arterburn LM, Hall EB, Oken H. Distribution, interconversion, and dose response of n-3 fatty acids in humans. American Journal of Clinical Nutrition. 2006;83(6 Suppl):1467S-1476S.
7. Tocher DR, et al. Omega-3 long-chain polyunsaturated fatty acids, EPA and DHA: bridging the gap between supply and demand. Nutrients. 2019;11(1):89.
8. Mozaffarian D, Wu JH. Omega-3 fatty acids and cardiovascular disease. Journal of the American College of Cardiology. 2011;58(20):2047-2067.
9. Bhatt DL, et al. Cardiovascular risk reduction with icosapentaenoic acid for hypertriglyceridemia. New England Journal of Medicine. 2019;380(1):11-22.
10. Yurko-Mauro K, et al. Beneficial effects of docosahexaenoic acid on cognition in age-related cognitive decline. Alzheimer's & Dementia. 2010;6(6):456-464.
11. Calder PC. Omega-3 fatty acids and inflammatory processes: from molecules to man. Biochemical Society Transactions. 2017;45(5):1105-1115.
12. Liao Y, et al. Efficacy of omega-3 PUFAs in depression: a meta-analysis. Translational Psychiatry. 2019;9(1):190.
13. SanGiovanni JP, Chew EY. The role of omega-3 long-chain polyunsaturated fatty acids in health and disease of the retina. Progress in Retinal and Eye Research. 2005;24(1):87-138.
14. EFSA Panel on Dietetic Products, Nutrition and Allergies. Scientific opinion on the tolerable upper intake level of eicosapentaenoic acid (EPA), docosahexaenoic acid (DHA) and docosapentaenoic acid (DPA). EFSA Journal. 2012;10(7):2815.
15. Dyerberg J, et al. Bioavailability of marine n-3 fatty acid formulations. Prostaglandins, Leukotrienes and Essential Fatty Acids. 2010;83(3):137-141.