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BY Bo Martinsen, MD Apr 13, 2016

Making Sense of Fish Oil Oxidation Values

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A few weeks ago, a fish oil manufacturer visited our office in Florida and gave us two samples of a supposedly super fresh, award winning fish oil. Would we be interested in using the oil in our Omega3 Innovations products, she asked?

The lab data showed that the oil had been analyzed by a national company. And the results indicated that the oxidation levels were extremely low. As a matter of fact, the oxidation levels were lower than any value I had ever seen recorded.

Of course, the data made me skeptical. So I tasted the oil. The strong flavoring, typically added to cover up any fishy taste, stayed on my tongue for hours.

Later that day, we analyzed the oil’s peroxide and anisidine values to determine its oxidation level. Instead of their claimed anisidine value of 0.1 (an impossible number), we found that their anisidine value was more than 200 times higher. As for the peroxide value, it was outside our measurable range, exceeding all freshness guidelines. No wonder the oil needed the heavy flavoring as a cover up!

So was this supposedly pristine oil a pure fraud or the result of ignorance?

The Rampant Rancidity Problem

If the above story sounds shocking to you, it’s actually not all that surprising when you look at the state of the omega-3 industry today. Studies from New Zealand, South Africa, and Norway have analyzed the omega-3 products on their markets. And the conclusions are concerning.

In New Zealand, researchers found that 83% of the products exceeded recommended industry peroxide levels (1). A similar study from South Africa reported the number at 80% for their over-the-counter fish oil supplements (2). In Norway, the homeland of fish oil, the results were even worse. A 2009 study demonstrated that over 92% of the products surveyed exceeded recommended industry levels (3).

Most troubling, however, were the results from a recent Canadian study. This study found that omega-3 products marketed towards children had the highest oxidation values of all (4).

Norwegian government study fish oil rancid rancidity fish krill oil brands

Understanding Peroxide, Anisidine & TOTOX Values

Thanks to scientists from across the world raising concerns over the volume of poor quality, rancid fish oil capsules, the omega-3 industry has recently started to push back. Many fish oil manufacturers, like the one who visited our office, are starting to talk about the oxidative status of their oil. And this, I believe, is a positive change.

For the consumer, however, it can also be confusing, especially when plenty of fish oil products claim to be fresh. What does it mean for an oil to be fresh? What is the best fish oil to take? How do we know what to trust?

Freshness and Rancidity Basics

Many people are not aware that freshness (or conversely rancidity) is not a purely subjective topic. It is something you can measure. In terms of omega-3 oils, the three most common measures of rancidity are peroxide, anisidine, and TOTOX values.

What do peroxide, anisidine and TOTOX values mean for oxidation?

When oils oxidize, they create new byproducts that don’t exist in the fresh oil. These byproducts typically give off the fishy taste and smell associated with old fish or turpentine. The peroxide and anisidine measurements give an indication of how many of these byproducts have formed in the oil. The TOTOX value, which is calculated using the peroxide and anisidine measurements, provides an overall picture of how fresh the oil is.

What should the peroxide, anisidine and TOTOX values of a fresh oil be?

As a rule, the lower the oxidation numbers, the fresher the oil. GOED (the omega-3 trade association) recommends a peroxide value of 5 mEq/kg and anisidine value of 20 mEq/kg as its upper limit (5). But it’s worth noting that some experts believe the values should be lower. Omega Cure® typically has a peroxide value of 0.1 – 0.3 mEq/kg, which explains why the oil has no fishy taste or smell. For a more in-depth discussion on optimal oxidation numbers, read this article.

What is the problem if an oil’s oxidation numbers are too high?

As oxidation occurs, an oil’s EPA and DHA content also decreases. Since the EPA and DHA molecules are the main workhorses of the omega-3 family, reduced EPA/DHA content means reduced efficacy of the oil (1). Furthermore, many scientists believe that excessively oxidized lipids could cause adverse health issues.

The peroxide, anisidine, and TOTOX values are not the only ways to measure an oil’s oxidation levels. However, these numbers are relatively easy to measure, requiring minimal equipment.

Still, the tests aren’t perfect. For instance, if an oil contains lots of flavoring or additives, it can affect the correct reading of the anisidine and TOTOX value.

Using the Taste and Smell Test

As helpful as oxidation values are in determining the freshness of an oil, you can’t just rely on the reported value to determine quality. This is because oxidation values are constantly changing. An oil might have a peroxide value well below the recommended 5 mEq/kg before encapsulation and bottling. But by the time that product has gone through its final processing and waited on a supermarket shelf for several months (or years, as the case may well be), that number will likely be much higher.

In fact, one study from Poland (Kolanowski et al) found that fish oil capsules developed peroxide levels 20% higher than their initial values within 22 days of storage. And these were fish oil supplements that had been stored at room temperature in air-tight containers with limited exposure to light (4).

How Do You Know If A Fish Oil Is Still Good?

While not foolproof, tasting and smelling the oil is probably the best way to assess a product for a regular consumer. Just like fresh fish, a truly fresh fish or cod liver oil should have no fishy taste or smell. And it shouldn’t need to be covered up by heavy flavoring or a gelatin capsule.

fresh fish cod liver oil no fishy taste smell
A truly fresh fish or cod liver oil has no fishy taste or smell.

Omega Cure Oxidation Values

For the nearly two decades we’ve been working with omega-3, Anne-Marie and I have firmly believed that to experience omega-3 benefits, you must use a fresh fish oil product.

For that reason, freshness has influenced all our decisions with regards to Omega Cure. We start with an ultra-fresh cod liver oil. And then, we’ve focused on maintaining that freshness by keeping Omega Cure cold during production, packaging the oil in small containers, and shipping directly to your home so as to avoid the store’s long shelf life requirements. We are also the only omega-3 manufacturer we’ve heard of that offers a completely unflavored liquid cod liver oil – a testament to Omega Cure’s freshness.

Why Omega3 Innovations Delivers the Best Brand of Fish Oil

This year, we’d like to take a step further by providing you with more information about Omega Cure’s oxidation numbers. Starting in May, when we bottle the oil, we will record the oxidation values of your oil batch and the date of bottling. Then, we will print these numbers on your Omega Cure bottle and Omega Cure Extra Strength boxes so you can see how your latest batch compares.

As stated above, an oxidation value is not a fixed number. Once you open your bottle of Omega Cure, it will – just like any other natural, fresh product – go rancid with time and exposure to oxygen. That’s why it is important that you use up your 8 oz. bottle within a 5 to 6 week period.

As the makers of your omega-3 oil, we believe we have the responsibility to provide you with as much information as we can about the freshness of your Omega Cure. In this industry, we want to be the first to take a stand for improved freshness transparency.

fresh full spectrum fish oil dose omega 3 innovations


1. Albert, Benjamin B. et al. Fish oil supplements in New Zealand are highly oxidised and do not meet label content of n-3 PUFA. Scientific Reports 5 (2015). Article ID 7928 (2015). doi:10.1038/srep07928. Epub 21 Jan. 2015.

2. Opperman M, Benade S. Analysis of the omega-3 fatty acid content of South African fish oil supplements: a follow-up study. Cardiovascular Journal of Africa. 2013 Sep; 24(8):297-302. doi: 10.5830/CVJA-2013-074.

3. Laupsa-Borge, Johnny. Velg Ferske og Naturlige Omega-3 Produkter. Helsemagasinet Vitenskap & Fornuft. 9 Dec. 2012.

4. Jackowski, Stefan A. et al. Oxidation Levels of North American over-the-Counter n-3 (omega-3) Supplements and the Influence of Supplement Formulation and Delivery Form on Evaluating Oxidative Safety. Journal of Nutritional Science 4 (2015): e30.doi:10.1017/jns.2015.21. Epub 4 Nov. 2015.

5. Fish Oil Standards/Testing Limits from Leading Organizations & Experts. NordicNaturals.

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