Purity Grade and Concentration

You are holding an Omega-3 pack and reading: "1,000 mg fish oil, of which 300 mg Omega-3". Sounds good — but what does it really mean? Omega-3 concentration and purity grade are two of the most important quality characteristics, making the decisive difference between an effective supplement and an expensive placebo. Those who cannot read the label figures correctly often pay for fillers rather than the actual active ingredients EPA and DHA. This article explains how to correctly interpret concentration data, which molecular form offers the best bioavailability and when highly concentrated products are genuinely worthwhile.

How Is EPA+DHA Concentration Declared?

Most Omega-3 products declare two values: the total amount of fish oil per capsule and the EPA+DHA content within it. The first value describes the total capsule fill; the second describes the genuinely active Omega-3 fatty acids. A classic standard product contains, for example, 1,000 mg of fish oil, of which 180 mg EPA and 120 mg DHA — i.e. 300 mg EPA+DHA, corresponding to a concentration of 30%.

Many manufacturers advertise the total fish oil amount (e.g. "1,000 mg"), which looks impressive at first glance. However, the only thing that matters is the EPA+DHA quantity. Only these two long-chain fatty acids are responsible for the health effects investigated in clinical studies. The remaining 70% of a standard fish oil consists of other fatty acids such as oleic acid, palmitic acid or stearic acid — not contaminants, but not active ingredients in the strict sense either.

Another common source of confusion: some manufacturers state "Omega-3" on the label, but mean the total amount of all Omega-3 fatty acids — i.e. EPA + DHA + DPA + ALA and others. Only EPA and DHA, however, are relevant for EFSA-approved health claims. Always check that the quantities of EPA and DHA are shown separately.

Standard Fish Oil vs. Concentrate: Which Is Better?

The difference between standard fish oil (approx. 30% EPA+DHA) and highly concentrated supplements (60–90% EPA+DHA) lies in the manufacturing process. Standard fish oil is obtained by pressing or extracting fish tissue and then refined to remove contaminants. The result is a natural oil with a moderate EPA+DHA content.

Concentrated fish oil undergoes an additional step: molecular distillation. Here the fatty acids are first converted into ethyl esters (EE form), then separated by distillation and EPA/DHA is enriched. The advantages: higher EPA+DHA concentration and more effective removal of contaminants such as PCBs, dioxins and heavy metals. The disadvantage: the ethyl ester process can reduce bioavailability (more on this below).

Type	EPA+DHA %	mg EPA+DHA / 1,000 mg	Capsules for 250 mg	Capsules for 1,000 mg	Capsules for 2,000 mg
Standard fish oil	30%	300 mg	1 capsule	3–4 capsules	6–7 capsules
Concentrate 60%	60%	600 mg	1 capsule (excess)	2 capsules	3–4 capsules
Super-concentrate 85%+	85%+	850+ mg	0.3 capsules (1 suffices)	1–2 capsules	2–3 capsules

For the basic EFSA recommendation of 250 mg EPA+DHA per day, a single standard capsule is theoretically sufficient. For higher intakes — such as the 2,000 mg per day that the EFSA claim on normal triglyceride levels refers to — significantly larger amounts are required. Here concentrates score considerably: instead of 6–7 standard capsules daily, just 2–3 concentrate capsules suffice for the same active ingredient quantity.

EPA vs. DHA: What Is the Right Ratio?

EPA (eicosapentaenoic acid) and DHA (docosahexaenoic acid) have different primary functions in the body. EPA acts primarily by regulating inflammation and is particularly relevant for cardiovascular health and mood. DHA is the structural component for the brain and retina, and is especially important during the development phase and for cognitive function. According to EFSA data, both are important — but their ideal ratio depends on the intended purpose.

The classic ratio in standard fish oil is around 3:2 (EPA:DHA), i.e. 180 mg EPA to 120 mg DHA. This ratio is well suited for general cardiovascular health and inflammation regulation. EPA-rich products (ratio 2:1 or higher) are often preferred for mood support, as EPA has been particularly well studied in animal model-based studies on depression. DHA-rich products (ratio 1:2 or DHA-dominant) are preferred for pregnant women, breastfeeding mothers and for infant brain development, since DHA is the primary Omega-3 building block in the brain.

Triglyceride, rTG or Ethyl Ester: Form Determines Bioavailability

The molecular form is one of the most frequently overlooked quality factors in Omega-3 supplements. In the body, fatty acids naturally occur as triglycerides (TG) — three fatty acids bound to a glycerol backbone. Natural fish oil is present in this TG form. During the concentration process, however, the fatty acids are first converted into ethyl esters (EE), which is cost-effective and efficient.

The decisive difference lies in absorption: studies show that TG form and re-esterified triglycerides (rTG) are absorbed significantly better than ethyl esters. A frequently cited study in the journal Prostaglandins, Leukotrienes and Essential Fatty Acids suggests that rTG fish oil may have up to 70% higher bioavailability compared with EE fish oil. More on absorption in the body in our article on Omega-3 metabolism.

How to recognise the form on the label: "Triglycerides" or "TG" indicates natural triglyceride form. "rTG" or "re-esterified triglycerides" designates the high-quality concentrate in triglyceride form — the best of both worlds: high concentration plus good bioavailability. "Ethyl esters" or "EE", or simply no indication of the form, often points to the cheaper ethyl ester format.

Form	Naturally occurring	Bioavailability	Concentration possible	Typical price
Triglyceride (TG)	Yes	High	Max. ~30%	Medium
Re-esterified TG (rTG)	No (processed)	Very high	60–90%	High
Ethyl ester (EE)	No	Low–medium	60–95%	Low
Phospholipid (krill oil)	Yes	Very high	Max. ~15%	Very high

Reading the Label Correctly

When purchasing an Omega-3 supplement, it is worth examining the label carefully — beyond the milligram figure printed in large text. Step one: look for individually stated EPA and DHA amounts. If it only says "Omega-3: 500 mg" without separating EPA and DHA, that is a first warning sign. Step two: divide EPA+DHA by the total fish oil amount. Result above 50%? You have a concentrate. Step three: check the molecular form — "TG", "rTG" or "EE". Step four: look for preservatives. Good products contain tocopherols (vitamin E) as a natural antioxidant.

A concrete example: Product A declares "1,000 mg fish oil, of which EPA 180 mg, DHA 120 mg, as ethyl ester". Product B declares "500 mg fish oil, of which EPA 250 mg, DHA 100 mg, as rTG, listed in the IFOS database". Although Product A has a larger capsule, Product B delivers more EPA, a better form and demonstrated quality control — at presumably a higher price, but with a better ratio of cost to actually absorbed active ingredient.

What is a fish oil certificate of analysis (COA), and how do you read one?

Short answer: A certificate of analysis is a laboratory report for one batch of oil. It lists what was measured (omega-3 content, oxidation, contaminants), the limit or specification and the result for that lot. Read it in this order: lot number and date, EPA and DHA against the label, oxidation against the limit, contaminants against the limit, and who did the testing.

The table shows a real example, a current IFOS product report. The brand is a US supplement company chosen only because its report is public; it is not a recommendation. Reports from other laboratories look different, but they should show the same kinds of results.

Source: IFOS product report, Life Extension Super Omega-3 EPA/DHA, lot C2600194, expiry 30.04.2028 (certifications.nutrasource.ca, read 31.10.2026). Dioxins, cadmium and arsenic are on the same report.

What to check on any COA:

• The lot number and expiry date match your bottle.
• EPA and DHA in mg match the label claim.
• Peroxide, anisidine and TOTOX are shown with a limit, see the TOTOX article.
• PCBs, dioxins and heavy metals are shown with limits, compared in the IFOS and GOED limits table.
• A laboratory is named and the methods are stated. A COA written by the brand itself, without a named laboratory, carries less weight than a third-party report.

A COA is a snapshot of one lot. You can find COAs on the brand's website, in the IFOS certified-products database, or by asking the brand for the report for your lot number.

Which omega-3 supplement has the best purity rating, and what does high purity mean?

Short answer: No single purity rating covers every omega-3 supplement, so there is no verified "most pure" product. "Purity" also means two different things: how concentrated the oil is (EPA+DHA as a share of the oil) and how clean it is (oxidation and contaminants). Cleanliness can be compared lot by lot, using a COA or an IFOS report against the same limits. Concentration is on the label: EPA and DHA in mg divided by the oil in mg.

• Concentration: standard fish oil is about 30% EPA+DHA, concentrates 60% or more (see the table above). The 2019 IFOS report for Bare Biology Lion Heart describes a minimum 60% omega-3 concentration as combined EPA and DHA.
• Cleanliness: compare TOTOX, PCBs, dioxins and heavy metals for the lot, not a brand slogan such as "ultra pure".
• Products with published batch reports: in our comparisons, Norsan Omega-3 Total and WHC UnoCardio 1000 are listed as IFOS-certified (best omega-3 oils compared), and Bare Biology Lion Heart has published IFOS reports (best omega-3 oil UK). Examples of reports are listed under which brands have IFOS certification.

When Is Highly Concentrated Omega-3 Worthwhile?

Highly concentrated Omega-3 supplements in rTG form are particularly useful when higher daily doses are required. According to EFSA, 2,000 mg EPA+DHA per day are needed to support normal triglyceride levels, and 3,000 mg for normal blood pressure values. With standard fish oil at 300 mg per capsule, this would mean taking 7 to 10 capsules daily — impractical for most people. With an 85% concentrate, the capsule count is reduced to just 2 to 4 per day.

People who are sensitive to the fish oil smell or to belching ("fish burps") also often benefit from concentrates in enteric-coated capsules, since the amount of accompanying fish fats is significantly reduced. Our Omega-3 requirements calculator helps you determine your personal daily dose and shows how many capsules of different concentrations you need.

For everyday prevention and basic EFSA provision, standard fish oil in TG form is, by contrast, a more cost-effective and perfectly adequate option. The decision ultimately depends on your personal needs, budget and desired convenience. Which specific products are recommended across different quality categories can be found in our detailed Omega-3 oil buying guide.

Important: concentration alone does not make a good product. A highly concentrated supplement with a poor TOTOX value (oxidised oil) is worse than a fresh standard product. Always assess several criteria together. More in our article on the 7 quality criteria for Omega-3 supplements and our article on Omega-3 certifications such as IFOS and MSC.

Frequently Asked Questions

External sources:
GOED Omega-3 Quality Standards (PDF)
EFSA — Scientific Opinions on Omega-3 Fatty Acids
IFOS product report, Life Extension Super Omega-3 EPA/DHA, lot C2600194 (2026), read 31.10.2026
IFOS product report, Bare Biology Lion Heart, lot LHL25341 (2019), read 31.10.2026