The Truth About Rancid Fish Oil

You hear a lot about the dangers of taking rancid fish oil.

You here about how bad it is for you. You hear about the dangers of oxidized fatty acids in your body from rancid fish oil. And of course, finally, you hear you should not take fish oil but some other marine-based Omega 3 product instead.

So it’s time to settle this argument once and for all, if that is possible. I say “if that is possible” because people believe what they want to believe and there is a lot of conflicting information. So what makes me the ultimate authority on this topic?

Simple; I can back up everything I say with real research. I can back up everything I say about my product and others I have tested with 3rd party, independent, unbiased testing. So I hold a challenge out to anyone who makes any of the products in question here. Test your products outside of your own company in the same way I do. And then I challenge you to make it public. Somehow I know that will not happen! Hint: I might already have test data, which I could easily provide to ruin reputations, but that is not my thing.

The problem in the supplement industry is that people are hiding behind marketing hype and out and out fallacies when it comes to making statements. Sadly, the letters PhD or MD behind the name do not stop this problem.

I say prove it. And I can prove what I say is true. Can you?

So let’s talk about how the myth of rancid fish oil got started and what it really means.

In 1974 my dad came home with a big jug of fish oil telling the whole family to start taking it because new studies showed it was good for us! Now one whiff of the stuff and you knew it was rancid. It didn’t just smell fishy, it smelled rotten fishy. I have no doubt it was rancid, but like a dutiful son I took it for a full two weeks before I finally ‘fessed up to my dad and said “I quit!”

He laughed and told me he stopped after two days.

I have no doubt that fish oil from the old days was rancid. I suspect there are some rancid brands out there still but they must be far fewer in number. There is an organization that looks at fish oil very closely called the IFOS. Their published recommendations for the highest grade fish oil is a product that contains less than 45 ppb PCB’s, dioxin and furan less than 1 ppt, oxidation less than 19.5 meq/kg. The last number, the 19.5, is the oxidation value. This is basically a measure of rancidity.

My fish oil 3rd party independent analysis is published for all to see here.*

Among any other values you might want to check, you can see we set our standards far tighter and better at less than 5.0meq/kg. for oxidation. As a matter of fact, this is actually reported as “less than” because it is below the limit of detection for this test.

So now you know my stuff is far cleaner and less oxidized than even the toughest international standard – what do you know about other fish oils? What do you know about krill? Nothing, except what they tell you on the endless blogs, videos and websites.

Now let’s look at the scientific basis for the “rancidity” argument.

Fats are integral parts of cell membranes and essential to inter/intracellular signaling throughout the body. They exist as long chain “fatty acids” in the membranes and are modified and released as chemical messengers when needed, both to the outside of the cell (eicosanoids and docosanoids) and inside the cell (resolvins).

These fatty acid chains are easily oxidized by free radical damage. This free radical damage takes place when a high energy particle, known as an electron, “bounces around” looking for a place to land and give up its energy. Free radical damage to fats is particularly problematic because the energy from that loose electron can be passed from one fat chain to another in a true “chain reaction” as that electron’s excess energy bounces from one fat chain to another doing damage all the way. Sounds bad, doesn’t it?

Well your body has several ways to interrupt that process.

Among the biggest ones are Vitamin E absorbing the free radical, a potent intracellular antioxidant known as glutathione absorbing the free radical, or the normal and ongoing replacement of fatty acid chains in the cells. Of these three, the role of importance is as follows: simple replacement, Vitamin E, and finally, glutathione. Please note this order only applies to fatty acids and not other things like proteins and carbohydrates where glutathione’s role is huge.

People who do not understand this say things like, “You need to take more Vitamin E if you are taking large doses of fish oil.” This is unsubstantiated pseudo-scientific nonsense, also known as BS. It’s a classic case of someone who does not understand fatty acid biology playing smart and reading a biochemistry textbook. I wish it were that simple. Just because a reaction exists in the body does not mean it is abnormal or damaging.

This simple fact that is left out is: You have to be Vitamin E deficient to actually not have enough Vitamin E in your body for this ever to be a problem. Just about everyone in the Western world has way more Vitamin E than is needed to handle this problem. I challenge anyone who makes associations with high dose vitamin E and high dose fish oil to show me the last case history of Vitamin E deficiency they have seen in the Western world. I also challenge them to show me a study where vitamin E improved the clinical outcomes of any dose of fish oil. There are none. And I can show you more studies that used fish oil alone and Vitamin E and fish oil that showed no clinical differences at all.

Zero, Zilch, Nada!

That does not mean that Vitamin E is worthless. It simply means you do not need to take “extra” Vitamin E to protect against rancid fish oil – especially if you use a high quality brand like mine that is already well below any standard for rancidity and oxidation out there. It also means that most of the reasons given for not taking high dose fish oil are the same pseudo-scientific nonsense.

So where does the current round of the rancid fish oil myth come from?

According to Harry Rice PhD, an Omega 3 researcher, it comes from a small number of animal studies using rancid VEGETABLE oil, not fish oil. These studies suggested that high doses of rancid vegetable oil (which is laden with inflammatory Omega 6 fats to begin with) might (not ‘do’) adversely affect the animals’ health. So someone decided to equate the vegetable oil findings in animals to Omega 3 findings in humans.

Actually, there are human studies where up to 8 grams a day of rancid – yes, rancid – fish oil was consumed for seven weeks had no adverse effects on human health.

Now I don’t recommend you do this experiment yourself because I did it back in 1974 and it’s not what I would call fun. But the bottom line is there is actually no proof of any damage to human health by consuming oxidized Omega 3’s. There are valid concerns about toxins in Omega 3 products as I have raised about krill and some of the “natural triglyceride” products in my lectures but that is a different issue.

Also, remember that the oxidation of fat is a natural process. The real way to guard against it is to take enough of your clean non-oxidized Omega 3 product to replace those fats as needed. This is the reason I do the Omega 3 finger stick test some of you have already done. The far bigger source of oxidation in the real world is too much Omega 6 fats from vegetable sources, not rancid fish oil!

Now you don’t have to take my word for it. You can look all this up on the internet for yourself. Just stick with scientifically based sources of information and not Dr. so-and-so’s web site! If you are wondering why some people will tell you differently, just ask this question: can they prove what they are saying other than by saying “because I said so and you should trust me”?

That is the reason there are studies and science. Because educated guesses and opinions are just that.

Make’em prove it! It’s your body and your health.


*Yes we are in the process of running another test right now as we speak and should have the results in less than six weeks. I will certainly post them proudly!

PS: As usual, there is a push among “foodies” to eat fish and not take fish oil, stating that supplements don’t work and fish does. I have never seen the magic ingredient in fish that makes the difference but I can tell you this – mercury is in fish and it ain’t a good thing!



Reference articles:
Effect of marine omega 3 fatty acids on methylmercury-induced toxicity in fish and mammalian cells in vitro.

Quality analysis of commercial fish oil preparations
This study found that over 50% of commercial Omega 3’s it tested did not meet concentration claims and over a quarter were over oxidized. No one has done a study on krill!

2 thoughts on “The Truth About Rancid Fish Oil”

  1. Thanks for clarifying on this point Dr Dave, there’s so much “scare mongering” and disputing info out there but when it comes to fish oil, you are truly the go-to expert for us! Your fish oil is unbeatable in terms of taste and quality and we’ve been taking 3-4 capsules daily for over 5 years now.

  2. Hi,
    Thanks for your article.
    Have you read the book, “The PEO Solution”, (2014), by Dr. Robert Rowen and Brian Peskin? It also provides great insight and documentation about Essential Fatty Acids Omega 3 and 6.

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