Green Pastures fermented cod liver oil (FCLO) has been considered the gold standard amongst cod liver oil supplements for a long time, but independent research by Dr. Kaayla T. Daniel on the oil has gotten a lot of heads turning and people thinking. The report has some quite shocking and worrying results and as someone who has been recommending and selling FCLO for years I was understandably very concerned. I’ve given the report plenty of thought and done some additional background reading on the subject to understand what the results mean, and below I’ve expressed my thoughts on these findings. You can read the whole 111 page report here if you like, but I’ve summarised her findings below.


Summary of Dr. Kaayla’s report

  • Cod liver cannot be fermented because fermentation requires carbohydrates.
  • 7 Samples of fermented cod liver oil were sent to 7 different labs to test for:
    • 6 Rancid bio-marker tests (varying results)
    • Biogenic amines – a product of rotting/ fermented foods with in some circumstances can be toxic
    • Vitamin content showing –
      • Moderate levels of vitamin A.
      • Low levels of vitamin D3.
      • Low/ insignificant levels of Co-Q10 and vitamin K.
  • DNA testing which shows the product is 100% Alaska Pollock.
  • Trans-fat content (suggesting heat processing/ vegetable oil).


How are cod livers fermented?

In biology, the fermentation process generally does require carbohydrates for the bacteria to feed on. This is true for milk, which contains lactose, and true for the probiotics in our gut which feed on the fibre we eat from plants. Yet cod livers don’t contain any carbohydrates in any significant quantity, which poses the good question of how can a cod liver ferment to produce oil?

Well, although fermentation usually requires some carbohydrates, there are many circumstances where it doesn’t. In fact, the term ‘fermentation’ is defined as ‘the chemical breakdown of a substance by bacteria, yeasts, or other microorganisms1, and there is no need for carbohydrates, although they are usually involved.

There are many fish products which don’t require carbohydrates to ferment, and fish products have been fermented for  years and years, in many countries without carbohydrates2. A great example is a very old East Asian fish sauce recipe which ferments small fish with sea salt to produce a sauce called ‘nuoc mam’ – which is very similar to how Green Pastures create their oil.

So, cod livers can be fermented.

For the record, Green Pastures state that their oil is made using salt, a fish broth starter, and livers. In industrial fermentation, the most common being yoghurt making, a ‘starter’ is a sample of which contains the bacteria cultures needed to produce the product. Using a starter broth ensures a consistent product is produced, and although we don’t know the specific bacteria Green Pastures use (industry secrets I guess), I am more than satisfied that the livers are indeed fermented.


Is fermented cod liver oil rancid?

A rancid fish oil is bad for you, there is no doubt about that, and there are some simple home tests you can do to check if your oil is rancid, but these tests don’t usually work for fermented cod liver oil. For starters, it’s brown, it’s fermented (so will smell different from other cod liver oils) and the ‘gels’ often have flavours/ scents in which would mask some of the rancid flavours/ tastes.

Besides, lab tests are much more accurate and reliable, so I was glad to see that a number of rancid bio-markers have been checked by Dr. Kaayla:


The peroxide value is a measurement of the amount of harmful lipid peroxides, and is an indicator for rancidity. FCLO scored extremely low for lipid peroxides from all lab tests – which is great. Dr. Kaayla says that this is unsurprising as the oil has been fermenting for so long that the lipid peroxides have probably decomposed into secondary and tertiary oxidation products.


Anisidine is one of the secondary metabolites mentioned above, and as peroxide levels go down, the levels of anisidine should go up (and then break down into tertiary oxidation products). Results from Labs 2, 4 and 7 all reported anisidine levels of 6.8, 13 and 3.44 – all of which is lower than the value Green Pastures shows on their site (which is 16). Lab 5 encountered problems in trying to measure anisidine due to colour of the product.

We don’t know what testing methods each lab used to test anisidine in their samples, but these results look very good and show low levels of anisidine (but Dr. Kaayla questions the reliability of the lab reports).


TOTOX is a measure of the total oxidation, and because the peroxide value and anisidine values are so very low, the TOTOX is also very low. This is good news for FCLO users – it doesn’t contain many oxidative products.

TBA (THIOBARBITURIC ACID)/ malondialdehyde (MDA)

MDA is a toxic product made when an oil by-product reacts with DNA. Dr. Kaayla admits that levels of MDA are not a reliable way to determine if fermented cod liver oil is rancid or not, but she tests for TBA/ MDA anyway. Lab 2 and 4 reported very low levels, whereas Lab 7 reported high levels (no results from other labs). Make of this what you will, but it is inconclusive, and even Dr. Kaayla says it means nothing for fermented cod liver oil (other than TBA/ MDA levels are low in 2/3 samples of course).

Free fatty acids content

There is no doubt that Green Pastures FCLO does contain some free fatty acids. This is something that Dr. Kaayla and Green Pastures agree on, but what they don’t agree on is what it means.

Fats are made up of a fatty acids attached to a glycerol backbone in a shape like an ‘E’ (see image) which is called a triglyceride, and it is in this form that you find fats in your food. In fact, this is the form most fats are found in fermented cod liver oil, and the presence of triglycerides is an indicator of a quality fish oil. In the digestive system they get broken down into glycerol and fatty acids by an enzyme called lipase, which allows them to be absorbed. Once absorbed, they are reassembled into a triglyceride.glycerol

Personally, I see no problem with eating fats as free fatty acids, because fats become free fatty acids in the digestive system anyway (you could even think of this as helping the digestive system).

Dr. Kaayla says that these free fatty acids are toxic to cell membranes, and so the body re-assembles them in the body. This may be true, but only once they have passed through the digestive system where they would have been converted in free fatty acids and glycerol anyway.

The presence of free fatty acids is an indicator that an oil is rancid because it shows the triglycerides have broken down, but by no means is it conclusive. The presence of these fatty acids has lead some marine oil experts to say that ‘FCLO is the most rancid oil they’ve ever tested’ (according to Dr. Kaayla) despite the other indicators of rancidity coming back negative.

Dr. Kaayla assumes that these free fatty acids show the oil is rancid (of which we have seen no real evidence for) and so say they are toxic. Yes, rancid fats are toxic, but we do not know that these fats are rancid.

For me, the presence of free fatty acids isn’t something to worry about, and only means that some of the triglycerides are effectively ‘pre-digested’ in a way my body would have done anyway.


The presence of aldehydes is another indicator that an oil has gone rancid. Dr. Kaayla didn’t test for aldehydes, but the Western A. Price foundation did send some samples to De Montford University for testing, which came back as ‘non-detectable’3. So again, good news for fermented cod liver oil.


Rancidity test summary

So, tests for rancidity are either good (not rancid) or inconclusive – hardly the dig at Green Pastures that Dr. Kaayla set out to do. Dr. Kaayla does say that these results would be expected for a product which has been fermenting for so long though (this does pose the question as to why they were tested for to being with…).


Amine content

Amines are not always bad – they give cheeses/ fish sauces/ wines their characteristics for example, but they do have toxic properties and indicate that proteins have ‘gone bad’ or have started to decompose (no surprise they are found in many fermented foods then).

Lab 4 found no amines, lab 2 found moderate but acceptable levels of amines, and lab 7 showed that the amines were very high (no results from other labs). This doesn’t show us much other than there is some variation in the products, which is to be expected. I wouldn’t want a high amine product, so the one high result is a concern, but these findings are far from being conclusive. I would be interested to know what a larger sample would show, but currently, I’m not too worried.


Vitamin content

Green Pastures say their product contains vitamin A, D and a number of quinones which many people (myself included) assume to mean there is a certain amount of co-enzyme Q10 and vitamin K. Dr. Kaayla tested the presence of all these vitamins.

Vitamin A

Dr. Kaayla’s report showed that vitamin A levels in her samples were 732 IU/ml (roughly 3600 IU per US teaspoon), which is well within what Green Pastures quote on their site4. I feel its worth pointing out here that throughout Dr. Kaayla report she quotes figures from the Green Pastures site, but in this case she incorrectly quotes figures from the Western A. Price site and ones which are “lobbed around the internet”, which are 10,000IU per teaspoon (I think, she gives no units).

In fact, the Western A.Price site quotes vitamin A levels in fermented cod liver oil to be 4,000 – 9,000 IU per teaspoon5. This means that Dr. Kaayla’s findings are a little less that what the Western A. Price foundation quote, but within the values Green Pastures have on their site. I do wonder why she didn’t quote Green Pastures’s figures on this…

Vitamin D

Dr. Kaayla’s report found that the vitamin D content of FCLO was 17.6 IU per gram, which is a lot less than the 310 – 1030 IU per gram Green Pastures state on their website.

There is a catch though – Vitamin D is a very difficult vitamin to detect and measure, and I’m not just saying this because Dr. Kaayla’s results show low vitamin D levels. Accurately measuring vitamin D is a problem laboratories have struggled with for a long time6,7. With this in mind, the very best way to measure the vitamin D content of a product, or rather, the vitamin D value of a product, is to feed it to someone for a fixed period of time, and measure changes in their vitamin D levels. If you control all other variables (food, sun light exposure etc) then the only way vitamin D levels will change is a result of the FCLO.

No one has this kind of data (sadly), but Green Pastures do use a rat bio assay to measure vitamin D, which is essentially the same test, but with rats not humans. Could there be a difference in humans and rats? Sure, what that difference is though, we don’t know. There are also mixed anecdotal reports online about how FCLO has or hasn’t helped individuals vitamin D levels, the scientific value of which is minimal, but could suggest that vitamin D content is very variable (more so than previously thought).

We don’t know what tests the labs did to determine vitamin D levels because the labs wanted this data, along with their identity, to remain anonymous. This makes determining the accuracy of their tests somewhat difficult. It would have been useful if the labs did the same rat bio assay to test for the vitamin D content in the fermented cod liver oil, as this would have shown some useful comparisons between the data Green Pastures gets, and what other labs get.

This being said, I am surprised that the labs came back with such low readings for vitamin D. The reason for this could be the method used to detect the vitamin D but I would like to see some more research into this, including rat bio-assays from different labs (or even human trials) to clear this up.

Vitamin K/ co-Q10

Vitamin K and co-Q10 are similar in their structures and both contain a quinone group. The presence of these nutrients is something that has made Green Pastures FCLO stand out from the crowd for a long time, and has made a good selling point for the products. Many fermented products such as cheese contain valuable amounts of vitamin K, so it would be expected that fermented cod liver oil would also contain reasonable levels too.

Dr. Kaayla sent her samples to lab 6, which is the ‘the world’s leading Vitamin K research centre’, and the quinone results came back pretty much as non-detectable. The quinone count was really very low, and this is very disappointing to hear. Quinones are not like vitamin D in their difficulty to measure, and so these results are worrying. Could it be that Green Pasutres had a bad batch, or are lying about their product? Only further tests can say for sure, but these preliminary results don’t look good.

Vitamin E

Tests for vitamin E are low, and this is to be expected for fish oil products. The vitamin E content of FCLO isn’t a selling point, and there is nothing surprising with these results.


Is FCLO from cod?

Dr. Kaayla noticed that the EPA and DHA ratios in Green Pastures fermented cod liver oil are not consistent with other ratios of cod liver oil. Oil from a cod has an EPA: DHA ratio 0.004: 0.1548) (or 2:77). Samples of Green Pastures cod liver oils come to around 2:1, which is very different.

Further research into the Green Pastures cod livers shows that the liver was from a fish called Alaskan Pollock.

Shock horror! The liver isn’t even from Cod!

Well, actually it is. If you want to get into the details of it, Cod is the name of a genus of fish, which means there are many types of cod, and one of these Cod fish is Alaskan Pollock9, which commonly found in the Northern Pacific Ocean.


Dr. Kaayla dismisses this and strongly implies that it is probably a cheap product imported from China, and not the high quality Cod caught in the Arctic that people think they pay for. This is actually quite unlikely – fish from China will probably be intensively farmed and given antibiotics (which Dr. Kaayla has found to not be present in her samples).

In fact Alaskan Pollock (which remember, is a Cod fish) can very well be fished from Arctic waters, and DNA samples recorded by the National Oceanic and Atmospheric Administration (NOAA) showed that Alaskan Pollock is present in the Arctic waters10.

Green Pastures don’t specify the species of cod they use, and only say that it is Cod from the Arctic, which from the information Dr. Kaayla has provided, looks to be true. There is currently no information to suggest that the livers are sourced from anywhere else other than unscientific speculation by Dr. Kaayla.


Trans-Fat in FCLO

Dr. Kaayla’s report does show that a sample contains 3.22% trans-fat, when you would expect there to be none. Dr. Kaayla says that the only way this could be present in the oil is to add a ‘thermally damaged vegetable oil‘. Yes, that would be one way, but the fermentation process could equally be a cause. It would be interesting to see what Green Pastures response to the presence of trans-fats in their product is, because you wouldn’t expect any, and it is a little concerning.


Final thoughts on the report

I always try and keep an open mind with reports like this, especially when I can see that a lot of time and effort has gone into them, but this report seemed flawed from the start. Before Dr. Kaayla did any research or saw any results she had decided that fermented cod liver oil was rancid. She says that “common sense says this product’s rancid” but “proving it is rancid, proved surprisingly difficult”. She has gone out to try and prove that she is right, rather than try and find if FCLO is healthy or not, and this typically leads to people finding results that suit their idea of what is right. The most famous example of this is in the Seven Country case study by Ancel Keys who went out to ‘prove’ the link between saturated fat consumption and heart disease – something which isn’t accepted as true today.

Setting out to prove your theory as Dr. Kaayla has done (combined with the unbelievable amount of terrible puns) somewhat diminishes the value and reliability of the research. When you believe you are right, you will find a way to show you are right (and Dr. Kaayla hasn’t even managed to do that conclusively).

My gut feeling is that Dr. Kaayla expected to find some Earth shaking results, but instead found very little, and has tried to dress them up to be more dramatic than they are.



Dr. Kaayla’s report is far from conclusive, and to be fair to Dr. Kaayla, she does say this is a preliminary report and more research is needed. The only concerns that this report has raised for me is the vitamin K, co-Q10 and trans-fat content of fermented cod liver oil, which I would like more answers for. I would also like to see some more research on the vitamin D content of fermented cod liver oil, but due to the complexity of this, I don’t expect to see anything conclusive any time soon.

I’ll keep my eye out for this information, and update this article accordingly if/ when it becomes available.

You might like to read Green Pastures response to Dr. Kaayla’s report here, which interestingly shows that Green Pastures invited Dr. Kaayla to their facility (all expenses paid) but received no reply from her.



1. Oxford dictionary. (2015). Oxford dictionary. Available: Last accessed 10/9/15.

2. G.Mazza. (2008). 1. In: Edward R.(Ted) Farnworth Handbook of Fermented Functional Foods, Second Edition. Florida: Taylor and francis. 21.

3. martin Grootveld. (2014). n/a. Available: Last accessed 10/9/15.

4. Dr. Jie Zhang. Test Data. Available: Last accessed 10/9/15.

5. David Wetzel. (2009). Update on Cod Liver Oil Manufacture. Available: Last accessed 10/9/15.

6. Andrew M Wootton. (2005). Improving the Measurement of 25-hydroxyvitamin D. Clin Biochem Rev. 26 (1), 33-36.

7. Fraser WD. (2013). Vitamin D assays: past and present debates, difficulties, and developments.. Calcif Tissue Int. 92 (2), 118-92.

8. Original Food Guide Pyramid Patterns and Description of USDA Analyses. Available: Last accessed 10/9/15.

9. Mark W. Coulson et al. (2006). Mitochondrial genomics of gadine fishes: implications for taxonomy and biogeographic origins from whole-genome data sets. Genome. 46, 1115-30.

10. CW and TA Mecklenburg. (2012). What we have learned about change in the distribution of fishes from the RUSALCA mission. Available: Last accessed 11/09/15.

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