Crash course on TOTOX value: How fresh is your Omega-3 fish oil?

Have you ever opened a fish oil capsule and been hit with a fishy smell or nasty burps? That is a tell-tale sign of oxidation – essentially, your omega-3 supplement going rancid. Enter TOTOX, a term you might spot on quality fish oil labels or lab reports. If you are health-conscious or shopping for omega-3 supplements, understanding the TOTOX value (a key freshness score) can help you avoid rancid fish oil and choose a product that is pure, potent, and pleasant to take.

In this crash course, we will break down what the TOTOX score means, how it is calculated, why a low TOTOX value is so important, and how you can ensure your omega-3 has a good TOTOX rating. By the end, you will know exactly what to look for – and why savvy supplement buyers insist on low TOTOX omega-3 oils for top quality.

What is the TOTOX Value in Fish Oil?

TOTOX stands for Total Oxidation. It is essentially an index of how oxidised (rancid) an oil is overall. Omega-3 fatty acids like EPA and DHA are highly prone to oxidation (they react with oxygen easily), and when they oxidise, they form peroxides and aldehydes that are not good for your health. The TOTOX value combines measures of these oxidation byproducts into one number. In simple terms, the lower the TOTOX value, the fresher and higher-quality the fish oil. A high TOTOX means the oil has oxidised significantly (think “gone bad”).

International industry standards have set clear benchmarks for freshness. The Global Organization for EPA and DHA Omega-3 (GOED) – a leading omega-3 trade association – recommends that quality fish oils stay below certain oxidation limits.

Specifically, good fish oil should have a TOTOX value no higher than 26.

In fact, GOED describes TOTOX as “the most important indicator to determine the quality of fish oil". This is because TOTOX gives a full picture of freshness, capturing both early-stage oxidation and later-stage breakdown products. It essentially answers the question: “How fresh (or rancid) is this oil?” A high-quality omega-3 supplement will have a very low TOTOX score, indicating minimal oxidation and a product that tastes and smells clean.

In summary: TOTOX is a single number that reflects how oxidised your fish oil is. Low TOTOX = fresh oil, high TOTOX = oxidised oil. For consumer reference, a TOTOX value in the low teens or single digits is excellent, whereas the upper limit for acceptability is around 26 per global standards. Anything higher and the oil is verging on rancid. Now, let us see why that matters for you.

Why does a low TOTOX score matter?

Choosing an omega-3 supplement with a low TOTOX value is not just about avoiding a fishy taste (although that is a big perk!). It is also about getting the health benefits you are paying for – and protecting yourself from potential downsides of oxidised oils. Here is why TOTOX matters so much:

• Preserves nutritional potency: Oxidation gradually destroys the beneficial omega-3 fatty acids in the oil. A rancid, highly oxidised fish oil delivers fewer health benefits because some of the EPA and DHA have broken down. In other words, an oil with a high TOTOX is not giving you the full omega-3 boost you think it is – you are not getting what you paid for.
• Protects your health: Beyond lost potency, consuming oxidised fats might carry health risks. Some evidence links oxidised oils to inflammation and other negative effects on the body. While research on humans is still ongoing, experts agree it is wise to minimise intake of rancid oils as a precaution. A fresh fish oil (low TOTOX) is not only more effective but also potentially safer than an oxidised one.
• Better taste and no “fishy burps”: The most obvious sign of oxidation is that awful fishy taste or smell. Fresh fish oil should be almost odourless and have a neutral taste, but oxidised fish oil develops a strong fishy, rotten smell and flavour. If your fish oil capsules repeat on you with fishy burps or smell foul when you cut them open, that’s a red flag of high TOTOX (rancidity). Low-TOTOX oils taste and smell much cleaner, so you’re more likely to keep up with taking them daily. (No one wants a supplement that makes them gag!)

In short, low TOTOX = fresh, effective, and pleasant, high TOTOX = degraded, possibly harmful, and nasty-tasting. It’s easy to see why keeping that TOTOX number down is crucial for both manufacturers and consumers. Manufacturers know rancidity is a quality failure that can ruin their reputation, and consumers rightfully expect their omega-3 to be fresh and safe. This brings us to how TOTOX is determined in the first place.

How is TOTOX calculated? (TOTOX formula explained)

The TOTOX value does not come out of thin air – it is calculated from two laboratory measurements: Peroxide Value (PV) and p-Anisidine Value (AV). Think of PV and AV as the two components of oxidation:

• Peroxide Value (PV) – This measures the amount of peroxides in the oil, which are primary oxidation products. When fish oil first starts to oxidise, it forms peroxide compounds. PV is expressed in “milliequivalents of oxygen per kilogram of oil (meq O₂/kg)”. A low PV means the oil has not accumulated many peroxides (early-stage oxidation is low). A high PV indicates the oil has started to go off and has lots of peroxides – though interestingly, if oxidation goes further, peroxides can break down again (so PV can drop later on, which is why we also need AV).
• p-Anisidine Value (AV) – This measures the level of aldehydes, which are secondary oxidation products that form after peroxides break down. AV is a dimensionless number (a result of a spectrophotometer test) indicating how much aldehyde-based breakdown has happened. High AV means the oil had significant past oxidation (even if PV is low now, the oil might have oxidised and then peroxides decomposed). Low AV means there are not many aldehydes, so later-stage oxidation is minimal.

Once we have PV and AV from lab tests, we plug them into the TOTOX formula to get the total oxidation value. The formula is:

TOTOX = (2 × PV) + AV.

Why double the PV? The peroxide value is given extra weight because peroxides are an early indicator that can later disappear as they convert into secondary products. By multiplying PV by 2, the formula ensures that an oil which is high in both peroxides and aldehydes will show a high TOTOX, even if one of those measures alone seems okay.

For example, if a fish oil has a PV of 2.0 meq/kg and an AV of 10.0, the TOTOX is (2×2.0) + 10.0 = 14.0. This combined number is essentially an oxidation score for the oil. (Note: Because PV has units and AV is unitless, the TOTOX value itself is treated as an index with no unit – it is just reported as a number).

TOTOX calculation quick table: Here is a handy comparison to see how PV and AV contribute to TOTOX:

In the table above, a premium omega-3 might have PV ~1 and AV ~3, giving a TOTOX of ~5 – an extremely low TOTOX indicating great freshness. By contrast, if an oil had PV 5 and AV 20 (each at the maximum allowed individually), the TOTOX would calculate to 30, which exceeds the recommended TOTOX limit of 26. This shows why TOTOX is such a useful index – it catches when both primary and secondary oxidation are high at the same time. In practice, manufacturers aim far below these limits to ensure quality.

To calculate TOTOX yourself (if you have a Certificate of Analysis in hand with PV and AV values), just apply the formula. But usually, reputable brands will do this for you and may even display the TOTOX value for transparency.

Good vs. bad TOTOX scores: what is acceptable?

So, what counts as a “good” TOTOX score for an omega-3 supplement? Broadly: the lower, the better. Global standards provide clear cut-offs to define freshness:

• Peroxide Value (PV) – should be ≤ 5 meq O₂/kg (this is the upper limit for primary oxidation in quality oils).
• Anisidine Value (AV) – should be ≤ 20 (unitless, indicating secondary oxidation level).
• TOTOX (Total Oxidation) – should be ≤ 26.

These guidelines are part of the GOED Voluntary Monograph and the Codex Alimentarius international standard for fish oils. Essentially, PV 5, AV 20, TOTOX 26 are the maximum values for a fresh, safe fish oil. If an oil stays at or below these, it is considered acceptable freshness. If it goes above, it is veering into rancid / substandard territory.

It is worth noting that in reality, good brands strive for much lower numbers. An oil right at the limit (PV 5, AV 20, TOTOX 26) is technically within standards, but it is not brag-worthy. Many premium fish oils will have TOTOX in the low teens or single digits, indicating a very fresh product. Some companies even advertise ultra-low TOTOX values (e.g. “TOTOX <10”) to show off their product’s freshness – because a lower TOTOX is always better for consumers.

On the flip side, what about bad TOTOX scores? Unfortunately, not all supplements on the market meet these ideal standards. Studies have found that a surprising number of omega-3 products exceed the recommended oxidation limits. For example, one analysis of fish oil supplements in New Zealand and Australia found about 50% of products tested had TOTOX values above the voluntary limit. In South Africa and other markets, a majority of over-the-counter fish oils were found to be rancid (with peroxide or TOTOX values beyond safe levels). That is concerning – it means many consumers could be taking capsules that are more oxidised than they should be. High TOTOX not only means potential health and taste issues as discussed, but it also signals poor quality control.

To avoid “bad” products, you want an omega-3 supplement with as low a TOTOX as possible – certainly well under 26. Ideally, ask for TOTOX values in the teens or below. If a product’s TOTOX is pushing up near the 20s, it might be time to question its freshness or look for a better option.

Ensuring your Omega-3 has a low TOTOX (what to look for)

Now that you know how important TOTOX is, the next step is being an informed consumer. How can you make sure the fish oil or omega-3 supplement you buy has a low TOTOX score and is truly fresh? Here are some tips:

• Check for transparency: Reputable omega-3 brands often disclose their TOTOX values or at least provide details on request. Some quality-focused companies print the TOTOX value on the packaging or their website, or include a “freshness guarantee”. Others might not list it outright on the label, but the information can be obtained via a Certificate of Analysis (COA). Look for brands that mention meeting GOED standards or refer to third-party testing – this is a good sign.
• Ask for the COA: The Certificate of Analysis is a lab report for a specific batch of product. A COA will list the peroxide value, anisidine value, and TOTOX for that batch, along with purity and omega-3 content. Quality brands will readily provide a COA to customers (some even have a QR code on the bottle or a link on their site). If a manufacturer is reluctant to share oxidation values, that’s a red flag. Top-notch omega-3 producers pride themselves on low TOTOX and will gladly show you numbers like “PV = 3, AV = 7, TOTOX = 13” on a report. Do not hesitate to request the COA for your supplement – it is your right to know what you are ingesting.
• Look for quality seals or standards: Certifications such as IFOS (International Fish Oil Standards) 5-star rating or GOED membership often require that products meet strict oxidation limits. If you see these, it is a sign the product likely has low TOTOX. Also, check the expiration/best-by date – companies set these dates based on how long the oil can stay under TOTOX 26. A far-out expiry plus a promise of freshness suggests they’ve formulated it to last without oxidising.
• Storage and packaging: Oxidation is accelerated by heat, light, and air. High-quality fish oils are usually packaged in ways that minimise exposure (dark bottles, blister packs, nitrogen-flushed containers). Once you buy a product, store it properly – a cool, dark place is best (some liquid fish oils even recommend refrigeration after opening). Proper storage ensures the oil’s TOTOX does not creep up before you finish the bottle. Follow any storage instructions on the label closely; they are there to help keep the oil fresh.

Finally, trust your senses too. If a capsule gives off a strong fishy odour or taste, do not ignore that – even if it is before the expiry date. It could indicate a higher TOTOX than expected. A great omega-3 supplement should have very little smell and no unpleasant aftertaste.

Conclusion: freshness first – demand low TOTOX

In the world of omega-3 supplements, TOTOX is the ultimate freshness score. It might sound technical, but it boils down to this: a lower TOTOX means a fresher, higher-quality fish oil that will deliver the health benefits you want without the fishy drama. Knowing about TOTOX empowers you to pick a better product.

So next time you are shopping for fish oil, be that savvy millennial-esque consumer who checks the details. Look at the brand’s info or ask customer service: “What’s the TOTOX value of this omega-3, and can I see the Certificate of Analysis?”. Good brands will applaud the question – it shows you care about quality, and they have nothing to hide. If they proudly answer that their TOTOX is, say, 5 or 10 (with proof), you can feel confident you are getting a fresh product. If you get blank stares or vague answers, you might want to choose a different brand.

Remember, omega-3 supplements are about improving your health. A rancid oil does the opposite – it is less effective and potentially irritating to your body. By demanding low TOTOX and checking for a COA, you ensure you are investing in a supplement that is worth every penny. Fresh, pure oil means no fishy burps, no nasty smells – just the omega-3 goodness you signed up for.

In a nutshell: TOTOX might be a small acronym, but it makes a big difference in the quality of your omega-3. Keep an eye on that TOTOX score – and you will keep rancidity out of your supplements, for a healthier and happier you.

References:

1. WhatsBehindTheDots – Omega 3: what the TOTOX value says about the quality of fish oilwhatsbehindthedots.com.
2. NFO Vitamins – TOTOX A-Z: the importance of being fresh (Quality indicators and standards for fish oil freshness)nfo.com.
3. NFO Vitamins – TOTOX A-Z: the importance of being fresh (Impacts of oxidation on nutrition, health, and sensory properties)nfo.com.
4. NFO Vitamins – TOTOX A-Z: the importance of being fresh (TOTOX formula and calculation example)nfo.com.
5. NFO Vitamins – TOTOX A-Z: the importance of being fresh (COA showing PV, AV, TOTOX values)nfo.com.
6. GOED/Oxidation study – Oxidation levels in fish oil supplements (showing many products exceed recommended limits)pmc.ncbi.nlm.nih.gov.