Oxidized Fish Oil - Should You be Concerned about Rancid Omega-3?

Oxidized Fish Oil - Should You be Concerned about Rancid Omega-3?

Oxidized Fish Oil - Should You be Concerned About Rancid Omega-3?


We got this question from a customer.

You might find the answer informative. 



It's known that most fish oils are oxidized (rancid) even though they are encapsulated. How can your company be sure there's no oxidation despite the capsule? 

Does your capsule have a proven material to prevent oxidation in room temperatures? I know only glass and metal can do this. 



Oxidation (or 'rancidity' as most of us call it) is not a Yes/No thing. There is no such thing as 'zero rancidity' or 'fully rancid.'  

All fish oils fall in a range in between. 

Fortunately, the best fish oil supplements are closer to 'zero rancid' than the smelly end of the spectrum. 

The link above takes you to IFOS Consumer Reports. There, you will find our products as well as other good fish oil brands who are confident enough in their products to have it tested and results publicly posted. Potency, purity, and rancidity values are all disclosed.


Three ways to express the oxidation of fish oil: 

  1. Peroxide value. It's a marker of short-term or recent oxidation, so a high Peroxide value suggests the EPA and DHA Omegas were recently exposed to oxygen.
  2. Acid value.
  3. Anisidine value. This is a marker of long-term oxidation. In really old oils, the Peroxide value will gradually drop and the Anisidine value will begin to climb. Example: a recent batch of our Triple Strength Omega-3 has an Anisidine value of 1.08, suggesting the oil is fresh (see below).

These are combined to produce a TOTOX or Total Oxidation number. This gives you an overall picture of how the oil has been handled over its lifetime. 

 IFOS Test results for InnovixLabs Triple Strength Omega-3 Lot # IL200425 Exp Date: 01/07/2023.

Triple Strength Omega-3 Fish Oil Oxidation Values 

A Totox value of under 20 is considered good or acceptable. 

If Totox is under 10, it is considered very fresh and relatively free of oxidation.

It is uncommon to find fish oil supplements with Totox less than 5. You'll never see zero Totox. 

While Totox of 5 to 10 is not unusual for our products, the Totox can regularly be just above 10 or so.

You may access this report from International Fish Oil Standards (IFOS) here

You can also find other 3rd party tested fish oil with oxidation numbers at the IFOS site.

Fish oil brands committed to quality are usually members of the Omega-3 trade groups GOED. And membership requires the brands to commit to certain quality standards. 

Standard TOTOX Limits

  • GOED members have to abide by an upper Totox limit of 26.
  • IFOS 5-Star rating require a Totox less than 19.5
  • Innovix will only accept fish oil raw material that is less than 10. 

Well-known large brands like Nordic Naturals, NOW Foods, and Carlson are GOED members. So are mid-size companies like us (Innovix Pharma), Wiley, and Barleans.

But many of the biggest fish oil sellers on Amazon are not GOED members.

To keep its members honest, GOED does regular testing. They tested 24 products from several different countries. 

Of the 24 products:

  • Four out of 24 failed Peroxide Value 
  • Three out of 24 failed Anisidine Value

So, GOED membership alone does not guarantee you will get fresh fish oil. You need to look for fish oils made by GOED members who also voluntarily send their products to be tested by IFOS. 

IFOS testing is expensive and voluntary. Only brands that are confident in their purity and potency will send their fish oil to IFOS. 

And if you struggle with insomnia, here's some pre-bedtime reading from GOED on the subject. 


Can Fish Oil Oxidize or Go Rancid After Bottling?

Not if it is stored correctly.

The oxidation of fish oil occurs mostly during bulk oil handling and manufacturing of the softgels. Not after pills have been put into bottles. 

Why? Because oil handling is when the Omegas can come in contact with oxygen, light, and possibly heat.

To avoid that, we produce our products under a nitrogen blanket. There is no oxygen anywhere in sight for the Omegas to react to.

The degree of oxidation that occurs after encapsulation is insignificant because gelatin acts as an oxygen barrier.

Of course, if you live in Florida and you store your opened fish oil bottle in your car...in the summer, well, then, all bets are off. The combination of heat and humidity can compromise the softgel and that can lead to rancidity.


Are Glass Bottles Better than Plastic Bottles?

No. As mentioned above, there is very little oxidation after putting pills in bottles. Therefore, the type of bottle is irrelevant.

Glass or metal makes no difference if the oil was mishandled prior to encapsulation.

Fish oil manufacturing and encapsulation has to be done with a near-paranoid level of oxygen avoidance.

We have a dozen years of shelf-life testing data, where we pull a retain bottle every 6 months to test its purity, potency, and freshness.

Our shelf-life testing confirms this: most of the oxidation happens during the raw material oil handing and encapsulation. 

Once the oil has been encapsulated and the pills put in bottles, it does not change the Totox much for a year or two, especially with the tocopherols (Vitamin E) added as anti-oxidants.

We produce a fresh batch every 4 to 6 months. This means the product is always fresh and you’ll rarely find a product that is even one year into its 3-year shelf life.


Should you Refrigerate Fish Oil Supplements?

No. If you plan on consuming the products soon after purchase, there is no need to refrigerate fish oils. 

Sure, refrigeration helps if you have a bottle and are not planning on consuming the softgels any time soon. In that case, we recommend freezing.

Refrigeration post-bottling only offers minimal advantage.

The critical point where ultra-low temperature is absolutely required is bulk oil transportation and encapsulation.

We ship our oil from Norway frozen and store our drums of oil at minus 50 F. At that ultra-cold temperature, along with a nitrogen or argon headspace, the drums of fish oil are good for decades.

But for finished bottles that will be consumed in a month or two…plastic bottles at room temperatures are perfectly fine.


Follow-up Question: 

Thanks for your educated responses. I'm happy to hear you're taking so many measurements against oxidation.

And I accept your points, especially sending a perfect product from your end.

I buy from iHerb and recommend my clients to buy your product from there too (which is why I might seem pedant).

It happened to me in the past companies sent me certificates at the time of production of different products. But for some reason, due to shipping, sending to the retailer, and storage, etc, I received an oxidized product. It only when the color changed in contrast to the manufacturer certificate of the batch, I knew something could happen in the way to my house.

You pretty much cleared up the packaging end. have you ever checked products sent via a retailer after arriving at the consumer? Oxidation levels months after the product leaves your facilities?

(2) You said " encapsulation is insignificant because gelatin acts as an oxygen barrier"

I was in communication with a fish oil company, where the owner told me gelatin only works in refrigeration. Above certain temperatures and humidity, gelatin is not perfect. Which can explain why many of your competitors have oxidized products on the shelves despite having gelatin capsules.



We do our best to emulate a commercially stored and shipped product in our shelf-life stability test.

We do this by real-time aging of products. We store 6 bottles of each new formula at warehouse conditions and pick one bottle every 6 months and ship them to a testing lab, mimicking a bottle being shipped from Amazon or iHerb to your residence.

At that rate, by the end of Year 3, we’ve tested all 6 bottles.

The FDA requires all products to be tested this way, but there is quite a bit of room for interpretation. 

Some products such as minerals can be tested using accelerated testing (heated aging chambers) but products with probiotics or Omega-3 should only be tested using real-world conditions because accelerated shelf-life storage will damage the contents.

So, to answer your question, ouer shelf-life stability testing mimics the process of a retailer shipping to a customer.

The total oxidation (Totox) goes up a little bit over the 3 year storage and shipping period, but it is very minor.

This underscores my previous statement that the critical exposure point for oxidation of fish oils is the during bulk oil manufacturing, storage, and transportation periods.

Once the oil is encapsulated in gelatin and bottled, the rate of oxidation is dramatically slowed or arrested when stored properly.


Is Gelatin a Good Oxygen Barrier?

Gelatin is a decent oxygen barrier – not perfect – but acceptable. If it had no oxygen barrier properties, all fish oil capsules would stink to high heaven!

It is good enough of an oxygen barrier that no one feels the need to nitrogen flush the bottles like we do the 55-gallon drums the bulk oils are stored and transported in.


Bottom-line: if you're short on time or don't understand all the details, just go with an IFOS tested product. It's the easiest way to guarantee that your fish oil is not rancid. 


Stuff that must be said:

Supplements may help, but supplements alone will not restore you to complete health. We think supplements are a small piece of the health puzzle. You cannot outrun a bad diet and inactivity with pills. Most of the heavy lifting involved in restoring your health will have to come from you in the form of healthy eating and lifestyle corrections. In these articles, we are merely sharing our excitement about nutritional science and doing our best to translate dense science into easy-to-read English. We geek out on nutrition science and we think you will too. We hope it makes you a more informed consumer. Our Legal Dept says the same thing in Legalese at the bottom of this page. Enjoy. 


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