Fish Oil and Omega-3 Supplements Explained: EPA, DHA, Oil Forms and Why Oxidation Is the Number That Matters

Fish oil is one of the most widely sold supplements in the world and one of the most misread. Two softgels can both say “1000 mg” on the front and deliver very different amounts of the fatty acids that matter, in different chemical forms, with very different freshness. This article explains what EPA and DHA are, how to read the numbers on an omega-3 label, how the oil forms differ, why oxidation is the specification that separates a good fish oil from a poor one, and what a brand owner in Malaysia or elsewhere should ask a manufacturer before putting a name on the bottle.

Quick answer: The useful number on a fish oil label is the combined EPA and DHA content per serving, not the “1000 mg fish oil” on the front. A standard 1000 mg softgel typically contains about 300 mg of EPA plus DHA, while concentrates contain 500 mg to 900 mg. Fish oil is sold as a health supplement in Malaysia, the EU and most ASEAN markets, and the same label-reading logic applies to krill and algal oils. Because the oil is highly unsaturated, it oxidises easily, so freshness markers (peroxide value, anisidine value and TOTOX) matter as much as potency. A brand owner should request a certificate of analysis that reports EPA, DHA, oil form and oxidation values for the actual batch, not the supplier’s typical specification.

Key takeaways

• “Fish oil 1000 mg” describes the whole oil. EPA and DHA, the active omega-3 fatty acids, are usually 30% of that in a standard oil and 50% to 90% in a concentrate.
• Omega-3 is sold in four main chemical forms: natural triglyceride, ethyl ester, re-esterified triglyceride and phospholipid. They differ in concentration, absorption and cost.
• Oxidation is the hidden quality problem. Industry standards from GOED and the Codex Alimentarius set a peroxide value ceiling of 5 meq/kg and an anisidine value ceiling of 20, and independent surveys have found many retail products exceed them.
• The regulatory story is favourable but narrow: the EU permits a heart-function claim for 250 mg of EPA plus DHA per day, and EFSA has judged supplemental intakes up to 5 g per day safe for adults. Disease-treatment claims remain off limits for a supplement.
• Plant omega-3 (ALA from flaxseed or chia) is not a direct substitute. Conversion to EPA and DHA in the body is low, so a vegan product that promises DHA needs algal oil.

Who this is for: founders planning an omega-3 or general wellness supplement, product teams writing a specification for a softgel, and marketing or regulatory staff who need to know which label numbers are meaningful and which claims are permitted.

What are EPA and DHA, and why are they the numbers that matter?

EPA (eicosapentaenoic acid) and DHA (docosahexaenoic acid) are the two long-chain omega-3 fatty acids that most of the published evidence on fish oil is actually about. They are found in oily fish such as anchovy, sardine, mackerel and salmon, and in the marine algae those fish feed on. The third omega-3, ALA (alpha-linolenic acid), comes from plants such as flaxseed, chia and walnut. The body can convert some ALA to EPA and a much smaller amount to DHA, but according to the National Institutes of Health Office of Dietary Supplements the conversion is very limited, which is why dietary guidelines treat marine omega-3 and plant omega-3 separately.

This matters for labels because “fish oil” is a whole oil. A crude oil from anchovy or sardine contains EPA and DHA alongside many other fatty acids, and the standard refined grade sold for decades carries roughly 18% EPA and 12% DHA. That is the origin of the familiar “1000 mg fish oil, EPA 180 mg, DHA 120 mg” softgel, which delivers 300 mg of EPA plus DHA per capsule. Concentrates are made by removing the non-omega-3 fatty acids, which pushes the EPA plus DHA share to 50%, 60% or more than 80% of the oil. A “1000 mg” concentrate and a “1000 mg” standard oil therefore differ by a factor of two or three in the ingredient the customer is paying for.

The practical rule for a buyer or a brand owner is to read the supplement facts panel, not the front label, and to compare products on milligrams of EPA plus DHA per serving. A label that gives only “omega-3 fatty acids” without splitting EPA and DHA, or gives totals per two or three softgels where a competitor gives them per one, is not necessarily wrong, but it is harder to compare and should prompt a closer look at the certificate of analysis. How to read that document is covered in the earlier guide on certificates of analysis and what they verify.

How do the omega-3 oil forms differ?

Omega-3 fatty acids are sold in four main chemical forms, and the form is written into the specification even when it never appears on the front of the pack. The differences are summarised below.

Form	How it is made	Typical EPA + DHA	Absorption	Relative cost	Usual source
Natural triglyceride (TG)	Refined and deodorised crude fish oil, structure unchanged	About 30%	Good; the form found in food	Lowest	Anchovy, sardine, cod liver, salmon
Ethyl ester (EE)	Fatty acids detached from glycerol and bound to ethanol, then concentrated by distillation	50% to 90%	Lower, especially on an empty stomach; improves with a fat-containing meal	Moderate	Anchovy, sardine (concentrates)
Re-esterified triglyceride (rTG)	Ethyl ester concentrate converted back onto a glycerol backbone	50% to 80%	Highest in most comparative studies	Higher	Anchovy, sardine (concentrates)
Phospholipid	Extracted from krill; omega-3 partly bound to phospholipids, naturally contains astaxanthin	About 10% to 25%	Good per milligram, but low total dose per capsule	Highest	Antarctic krill
Algal oil (TG)	Fermented microalgae, usually DHA-rich with some EPA; vegan	About 20% to 55%	Comparable to fish TG oil	High	Schizochytrium and related species

Two analysis points follow from the table. First, concentration and form are linked: it is not possible to reach 80% EPA plus DHA without going through the ethyl ester step, so a high-potency product is either an ethyl ester or a re-esterified triglyceride, and the specification should say which. Second, the absorption differences are real but often overstated in marketing. Comparative studies generally rank re-esterified triglyceride at or above natural triglyceride and ethyl ester below both, with the gap narrowing substantially when the capsule is taken with a meal that contains fat. For most consumers the bigger variable is whether they take the product consistently, not which ester it is.

Why is oxidation the specification that matters most?

EPA and DHA have five and six double bonds respectively, which is exactly what makes them biologically useful and chemically fragile. Exposure to oxygen, heat and light breaks those bonds down into peroxides, which in turn break down into aldehydes and other secondary products. The result is the rancid smell and “fishy” aftertaste associated with poor fish oil, a loss of the EPA and DHA that were measured at manufacture, and compounds that the evidence suggests are not merely unpleasant but may undo part of the benefit.

The industry measures oxidation with three numbers. Peroxide value (PV, in milliequivalents of oxygen per kilogram) measures the primary oxidation products. Anisidine value (pAV) measures the secondary aldehydes that peroxides turn into. TOTOX is a combined index calculated as twice the peroxide value plus the anisidine value, so that an oil cannot hide a history of oxidation by having a low peroxide reading at the moment of testing. The GOED Voluntary Monograph, the quality standard published by the Global Organization for EPA and DHA Omega-3s and used by most reputable refiners, sets PV at no more than 5 meq/kg, pAV at no more than 20 and TOTOX at no more than 26. The Codex Alimentarius Standard for Fish Oils (CXS 329-2015), the international food standard, applies the same 5 meq/kg peroxide and 20 anisidine ceilings.

These limits are not always met on the shelf. A 2015 study published in Scientific Reports tested fish oil supplements sold in New Zealand and found that the majority exceeded at least one of the recommended oxidation limits, and that only a small minority contained the EPA and DHA stated on the label. Market surveys since then in other countries have reported similar, if less extreme, findings. The point for a brand owner is that the oxidation numbers on a supplier’s typical specification describe the oil when it left the refinery, not the softgel after encapsulation, warehousing, shipping through a tropical port and three months on a retail shelf.

Manufacturers control oxidation at several points. The raw oil is stored cold under nitrogen and used within a defined window. Antioxidants, usually mixed tocopherols or rosemary extract, are added at refining or at blending. Encapsulation lines flush the oil with nitrogen and keep exposure time short. The softgel shell itself is a barrier, which is why oxidation in a sealed capsule proceeds far more slowly than in a bottle of liquid oil once opened. Opaque packaging, induction seals and desiccant complete the picture. The evidence that all of this worked is an oxidation test at release and again at the stability time points, which is part of the product testing that a contract manufacturer runs before and after launch rather than something a brand owner can check by opening a capsule and smelling it. The general discipline of putting a product through real-time and accelerated conditions is described in the guide to stability testing and shelf life.

What about mercury, PCBs and other contaminants?

Mercury is the contaminant consumers ask about most and, counter-intuitively, the one that refined fish oil is least likely to contain. Mercury in fish binds to protein in the muscle, not to the oil, and the refining steps remove what little carries over. Independent testing programmes consistently report mercury in finished fish oil at or near the limit of detection. The contaminants that genuinely matter are the fat-soluble ones: dioxins, dioxin-like PCBs and non-dioxin-like PCBs, which accumulate in fish fat and therefore in the oil. Molecular distillation, the same process used to make concentrates, is also the main tool for stripping them out, which is one reason concentrates from reputable refiners are often cleaner than crude oils.

The species used matters too. Anchovy and sardine are small, short-lived and low in the food chain, so they accumulate less than long-lived predators such as tuna. That is why most of the world’s supplement-grade fish oil comes from the Peruvian anchovy fishery rather than from salmon or tuna, whatever the picture on the box suggests. A brand owner should ask for the heavy-metal and PCB results for the batch alongside the oxidation data. The wider framework for contaminant limits in supplements, and how the tests are run, is explained in the article on heavy metals and microbial limits in cosmetics and supplements.

What can a fish oil brand legally claim?

The evidence base for EPA and DHA is large, but regulators have been selective about which claims it supports. In the European Union, Commission Regulation (EU) No 432/2012 authorises the claims that EPA and DHA “contribute to the normal function of the heart” at a daily intake of 250 mg of EPA plus DHA, and that DHA “contributes to maintenance of normal brain function” and “normal vision” at 250 mg of DHA per day. Those conditions of use are a useful benchmark anywhere: a product that delivers less than 250 mg of EPA plus DHA per daily serving is below the level at which even the most permissive general claim is authorised in Europe.

On the safety side, the European Food Safety Authority concluded in its 2012 scientific opinion on the tolerable upper intake level of EPA, DHA and DPA that supplemental intakes of EPA and DHA combined up to 5 g per day do not raise safety concerns for adults. That gives formulators a wide margin, though high doses interact with anticoagulant medicines and products aimed at that level should be positioned with care.

In Malaysia, omega-3 softgels are regulated by the National Pharmaceutical Regulatory Agency (NPRA) as health supplements, which means product registration before sale and a defined list of permitted general health claims. Claims to treat, prevent or cure a disease, including heart disease, arthritis or depression, are not available to a supplement in Malaysia, the EU or the United States regardless of what individual studies report. The boundary between a permitted structure-function claim and a prohibited disease claim is set out in the earlier article on what health and beauty brands can legally say.

What should a brand owner specify when developing an omega-3 product?

A good omega-3 brief treats the oil as the product and the softgel as the delivery system, and specifies both. For the oil: the source species and fishery, the form (natural TG, EE, rTG, phospholipid or algal), the minimum EPA and DHA in milligrams per capsule rather than as a percentage, the oxidation limits at release and at expiry, contaminant limits, and the antioxidant system. For the capsule: shell material, fill weight, and the overage policy.

Shell material deserves attention in this region. Most softgels use gelatin, which may be bovine, fish or porcine. For a halal-certified product the gelatin source must itself be halal-certified and documented through the supply chain, and the fish gelatin option is often chosen precisely to simplify that. Plant-based shells from modified starch and carrageenan are available for vegan algal-oil products but run on different equipment settings and usually cost more. These are the kinds of decisions a supplement manufacturer that runs its own softgel encapsulation works through with a brand at the development stage, because changing shell material after launch means re-running stability. The broader comparison of capsules, tablets, powders and gummies, including why omega-3 is almost always a softgel, is in the guide to choosing a supplement dosage form.

The last item, overage, is the quiet determinant of whether a label is true at expiry. Because EPA and DHA decline slowly over shelf life even in a well-made softgel, manufacturers typically fill slightly above the labelled amount so that the product still meets its claim at the end of its shelf life. The size of that overage should be justified by stability data, not guessed, and the certificate of analysis should show the measured EPA and DHA for the batch, not the target.

Common mistakes with omega-3 products

• Comparing on oil weight. A 1000 mg softgel of 30% oil and a 1000 mg softgel of 60% concentrate are not the same product. Compare on EPA plus DHA per serving.
• Accepting a typical specification instead of batch data. Oxidation values and potency drift between batches and over time. Ask for the certificate of analysis for the lot being bought.
• Calling flaxseed oil an omega-3 substitute. ALA is an omega-3 but converts poorly to EPA and DHA. A vegan DHA product needs algal oil.
• Clear bottles and warm warehouses. Light and heat accelerate oxidation. Opaque packaging and controlled storage are part of the formula, not an afterthought.
• Borrowing claims from clinical trials. Studies using prescription-strength EPA at several grams per day do not license a 300 mg supplement to make cardiovascular treatment claims.

Frequently asked questions

How much EPA and DHA should a fish oil capsule contain?

There is no single required amount, but 250 mg of EPA plus DHA per day is the level at which the EU authorises the general heart-function claim and a common benchmark for an adult maintenance dose. A standard 1000 mg softgel gives about 300 mg; concentrates give 500 mg to 900 mg. Check the supplement facts panel for the figures per serving and per capsule, as the two are often different.

Is triglyceride fish oil really better than ethyl ester?

Re-esterified triglyceride oil is generally absorbed somewhat better than ethyl ester oil, and the difference is largest when the capsule is taken without food. With a fat-containing meal the gap narrows considerably. Ethyl ester is a legitimate, widely used form and is how most high-concentration oils are produced; the issue is disclosure, so the form should be stated in the specification and ideally on the label.

What does TOTOX mean on a certificate of analysis?

TOTOX is a total oxidation index calculated as twice the peroxide value plus the anisidine value. It captures both the early and later stages of oxidation in one number. The GOED monograph sets a maximum of 26; a freshly refined oil is often well below 10. A high TOTOX with a low peroxide value usually means the oil oxidised earlier and the peroxides have already broken down.

Does fish oil contain mercury?

Refined fish oil contains very little mercury, because mercury binds to fish protein rather than fat and is removed during refining. The contaminants that need to be checked in fish oil are the fat-soluble ones, mainly dioxins and PCBs, which are reduced by molecular distillation and should be reported on the certificate of analysis for each batch.

Can a vegan product provide EPA and DHA?

Yes, through algal oil, which is produced by fermenting microalgae and is typically rich in DHA with a smaller amount of EPA. Flaxseed, chia and other plant oils provide ALA, which the body converts to EPA and DHA only in small amounts, so they are not a like-for-like replacement. A vegan product also needs a non-gelatin softgel shell.

Why do some fish oil capsules cause fishy burps?

Reflux of oil from the stomach is the usual cause, and it is more common with larger doses taken on an empty stomach. Oxidised oil makes the taste much worse, so persistent fishy repeat can be a warning sign of a poorly stored or ageing product. Enteric-coated softgels, taking the capsule with a meal, and keeping the bottle cool and closed all reduce the problem.

Is fish oil halal?

The oil itself is from fish and is generally accepted as halal, but the finished softgel depends on the gelatin shell and the processing aids used. For a halal-certified product in Malaysia the gelatin must come from a halal-certified source, commonly fish or halal-slaughtered bovine, and the full supply chain is documented for JAKIM certification. The requirements are described in the guide to halal certification for health and wellness products.

Sources and limitations

This article draws on the GOED Voluntary Monograph, the Codex Alimentarius Standard for Fish Oils (CXS 329-2015), Commission Regulation (EU) No 432/2012, the EFSA 2012 opinion on the tolerable upper intake level of EPA, DHA and DPA, the NIH Office of Dietary Supplements omega-3 fact sheet, and Albert et al., Scientific Reports (2015). Concentration ranges and cost comparisons are typical industry figures for orientation and vary by supplier. Regulatory positions are summarised as at October 2026; registration requirements and permitted claims differ by market and should be confirmed with the relevant authority or a regulatory adviser before launch. This article is educational and is not medical advice.

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Creaton Poh is the pen name of Poh Tze Kheng, founder of ORIZI Group — one of Malaysia's most comprehensive one-stop OEM, ODM, private label and contract manufacturing groups, spanning skincare, cosmetics, personal care, perfume and fragrance, supplements, functional food and nutrition, pet care, home care and medical devices. Across six specialised companies and three manufacturing divisions, the Group brings together 20+ years of industry experience, 5,000+ formulations, and internationally recognised quality, manufacturing and regulatory standards. These articles are written to educate, not to promote.

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