A tin of sardines, a spoonful of ground flaxseed and an algae-based capsule may all be described as sources of omega-3. Yet EPA, DHA and ALA: what's the difference? The answer matters when choosing foods or supplements for your own needs, because these three fats are related but not interchangeable.
Omega-3s have an established place in a balanced diet, with roles in normal bodily function that vary according to the particular fatty acid and the amount consumed. Knowing which form you are looking at helps you read a label beyond the headline claim and choose a product that best suits your dietary needs and health goals. Once you know the difference, our guide to choosing an omega-3 supplement walks through picking one.
EPA, DHA and ALA: the key difference
EPA, DHA and ALA are all polyunsaturated omega-3 fatty acids. ALA, or alpha-linolenic acid, is the shorter-chain plant form. EPA, or eicosapentaenoic acid, and DHA, or docosahexaenoic acid, are longer-chain forms found principally in oily fish and marine algae.
The body cannot make ALA, so it is considered essential and must come from food. Only a small proportion of dietary ALA is converted to EPA, and conversion to DHA is very limited in most adults. That is why a diet rich in flaxseed, chia or walnuts should not automatically be treated as nutritionally identical to one containing oily fish or a direct EPA and DHA supplement. ALA contributes to the maintenance of normal blood cholesterol levels. The beneficial effect is obtained with a daily intake of 2g ALA.
EPA and DHA are often grouped together on packaging as 'marine omega-3'. They frequently appear in the same fish oil capsule, though the proportion of each can be very different. The total amount of fish oil is less informative than the actual amounts of EPA and DHA provided per daily serving.
ALA: the plant-based essential
ALA is found in flaxseed and flaxseed oil, chia seeds, hemp seeds, rapeseed oil, walnuts and soya-based foods. It contributes to normal blood cholesterol levels when consumed at an appropriate daily intake as part of a healthy lifestyle.
For those following a vegetarian or vegan diet, these foods are valuable regular sources of omega-3. Freshly ground flaxseed is often more practical than whole seeds, as it is easier for the body to access. Oils and seeds are also calorie-dense, so a modest portion used consistently is usually more useful than an occasional large serving.
However, ALA supplements and foods do not provide DHA directly. This distinction is particularly relevant for people who do not eat fish and want a reliable source of the long-chain omega-3s. Algae oil offers a plant-based route to DHA and, in some formulations, EPA too. It is grown from marine microalgae, most commonly a strain called Schizochytrium - which is, in fact, where the fish get their omega-3 in the first place. That makes algal oil a direct source rather than a second-best substitute, and our vegan omega range covers the options.
EPA: and heart health
EPA is a major component of oily fish such as salmon, mackerel, herring, sardines and anchovies. It is also present in krill oil and certain algae oils. EPA and DHA together contribute to the normal function of the heart. The beneficial effect is obtained with a daily intake of 250mg of EPA and DHA combined.
Some higher-strength formulations are designed to provide a more substantial EPA intake. Higher-strength products may be appropriate for some individuals following advice from a healthcare professional but high-dose products are not a substitute for clinical care or prescribed treatment. The right amount depends on your diet, health history and the reason you are taking it.
EPA is sometimes selected by shoppers who want a fish oil with a higher EPA-to-DHA ratio. There is no universally superior ratio for every person. A product formulated to provide different proportions of EPA and DHA can be appropriate within a well-chosen routine.
DHA: the omega-3 associated with brain and vision
DHA is particularly concentrated in the brain and retina. A daily intake of 250 mg of DHA contributes to the maintenance of normal brain function and normal vision. These are established claims, but they should be understood in context: supplements support a balanced diet and healthy habits, rather than promising a noticeable short-term change.
DHA is also commonly considered during pregnancy and breastfeeding. During pregnancy and breastfeeding, maternal DHA intake contributes to the normal brain and eye development of the foetus and breastfed infant. Higher-DHA formulas are grouped in our pregnancy range. Anyone who is pregnant, planning a pregnancy or managing a health condition should seek individual advice from a pharmacist, midwife, GP or other qualified healthcare professional before beginning a supplement.
Fish provides DHA naturally, while algae oil is an effective vegetarian and vegan source. Algae-derived omega-3 supplements may be suitable for people who avoid fish, including many with fish allergy, but anyone with a confirmed food allergy should check product ingredients and seek advice if unsure.
Food first, then choose the right supplement format
Most people can meet their omega-3 needs through a healthy, balanced diet. Oily fish offers more than omega-3, including protein, vitamin D in some varieties and other micronutrients. For many adults, including two portions of fish each week, one of them oily, is a sensible dietary foundation. Variety matters: rotate choices such as sardines, salmon, trout and mackerel rather than relying on one species alone.
A supplement can be a considered addition where fish is rarely eaten, dietary preferences limit access to marine omega-3s, or a specific DHA or EPA intake is desired. The label should make your decision straightforward. Look for the actual milligrams of EPA and DHA in the daily dose, rather than judging a formula by the size of its capsule or the amount of oil alone.
Capsules, liquid oils and gummies each have practical advantages. Capsules are discreet and often provide a concentrated dose; liquids can suit those who dislike swallowing capsules; and gummies may be convenient, though they can contain lower omega-3 amounts and added sweeteners. Taking fish oil with a meal can improve comfort for those prone to a fishy aftertaste or reflux.
What to look for on an omega-3 label
A premium omega-3 supplement should be clear about its source, daily serving and EPA and DHA content. Fish body oil, cod liver oil, krill oil and algae oil are distinct ingredients, not simply different names for the same thing.
Cod liver oil deserves particular attention because it naturally contains vitamins A and D as well as omega-3. Cod liver oil should not be combined with other vitamin A-containing supplements without checking total intake. During pregnancy, products containing retinol, including many cod liver oils, are generally avoided unless specifically recommended by a healthcare professional.
Quality also concerns freshness and traceability. Omega-3 oils are delicate and can oxidise over time, which affects taste and quality. Choose products stored in protective packaging, follow the storage directions carefully and do not use an oil that smells persistently rancid. For fish-derived products, clear sourcing and purification information can provide useful reassurance.
A few sensible precautions
Omega-3 supplements are well tolerated by many people, but they are not suitable for every circumstance. Speak to a pharmacist or GP before taking a higher-dose omega-3 supplements if you use anticoagulants or antiplatelet medicines, have a bleeding disorder or are managing a long-term condition. Tell your healthcare team if you take omega-3 supplements before surgery, as they will advise whether any medicines or supplements should be stopped. Those with a fish or shellfish allergy should check both the source and allergen statement with care.
It is also wise to avoid doubling up unintentionally. A multivitamin, cod liver oil and separate fish oil capsule may each contain relevant nutrients. Reviewing the full routine is often the simplest way to make sure every product has a clear role - our guide to vitamin and mineral pairing covers avoiding overlap.
The most useful choice is rarely the one with the largest number on the front of the pack. It is the omega-3 format, source and daily dose that fits your diet, preferences and healthcare needs - and that you will be happy to take consistently. If you decide a supplement is right for you, our omegas and oils range includes products providing EPA, DHA and plant-based omega-3 options.