Fish oil or cod liver oil? Taking stock of the differences

By: Nick Noloboff

People often ask: 'What’s the difference between “fish oil” and “cod liver oil”?'

The simplest answer is

  • True cod liver oil is extracted exclusively from the livers of cod
  • Fish oil is extracted from the body flesh of fatty fish like sardines, anchovies, mackerel, etc

Type of fish is the main difference between these two types of omega-3s, but it’s a relevant difference because not just any fish is appropriate to use when making an omega-3 product.

The most beneficial omega-3 fats go by their abbreviations “EPA” and “DHA”. These particular fats have a molecular structure that’s easy for the body to use and offers unique health benefits to the heart, brain, eyes, joints, nervous and immune systems, and more.


EPA and DHA are most abundant in marine sources like algae and cold-water fish, which is why salmon is often recommended as a great dietary source of omega-3s.


Difference in EPA & DHA ratio

Cod liver oil and fish oil are both good sources of EPA and DHA, but they provide slightly different ratios of these fats.

  • Cod liver oil contains about 9% EPA and 14% DHA
  • Fish oil contains about 18% EPA and 12% DHA.

Cod liver oil also naturally contains modest amounts of vitamin A. Here are some other things to consider when choosing between a cod liver oil and a fish oil product.

Cod liver oil is considered the classic omega-3 supplement.

Oil from Arctic cod has been used to keep people health in Scandinavian countries for centuries, and this tradition is a key reason that many people today stick with cod liver oil. It may also be why cod liver oil is less often used to make concentrated omega-3 products.


Concentration deliberately manipulates the natural ratio of EPA to DHA fats in order to achieve a specific level of one or the other. Fish oil is more commonly found as concentrates, and there can be very good reasons why someone may want an EPA-dominant or a DHA-dominant fish oil.

For example, research suggests that during pregnancy, DHA is especially important. But for purists, cod liver oil is the classic choice.



Considering sustainability

Cod species are also large (and tasty!) fish. The livers of cod used to make supplements come from fish whose fillets are used as food for humans. In other words, using the liver for its oil helps utilize more of the whole fish.

The process is somewhat different with fish oil made from anchovies and sardines, which are much smaller fishes than cod. The omega-3 oil is extracted from their bodies so there’s not much left once this process is done. You certainly cannot put what’s left into tins!

However, in an effort to utilize the whole fish, the remains may be used for pet food or for fish meal to feed farmed fish.

Anchovies and sardines are considered especially sustainable species for fish oil because they come from a relatively large biomass and are quick to reproduce.

Avoid fermented cod liver oil

Both cod liver oil and fish oil offer beneficial marine omega-3s.

One thing to avoid, however, is fermented cod liver oil. There are a number of concerns with these products. To begin, fermentation renders them rancid, which is why they smelly so ‘fishy’. But it’s not just the smell that is a concern; rancid fish oil contains unstable fatty acid molecules which are unhealthy to consume.

Fresh cod liver oil will always contain more DHA than EPA, but analyses of fermented products show that this is not the case. They may contain nearly 60% free fatty acid molecules, rather than the 100% natural triglyceride molecules that the human body has evolved to recognize and efficiently use. Fermentation is great for many foods, but cod liver oil isn’t one of them. Fresh is always best.

What to look out for when selecting Omega-3 products

Despite the differences between cod liver oil and fish oil, some basic rules of thumb apply when selecting any omega-3 product.

Look for a product that meets international standards for purity (safety) and quality. Third-party test results should be made available to customers to confirm things like oil freshness, potency, and the removal of heavy metals which accumulate in fish over time.

If your current product is a fish oil soft gel with no added nutrients, try biting into the capsule. If the oil tastes bad, or very fishy, it’s probably not fresh.

Also look for triglyceride-form products no matter what fish is used to make them. This is the form in which omega-3s naturally exist in fish, and what the body uses best. If all these check out, your choice of cod liver oil, or fish oil, is likely a good one.


About the author

Nicholas Noloboff, MA is a Senior Writer at Nordic Naturals, where he supports the company’s marketing and education efforts. He has graduate degrees in the social sciences which inform his writing on health and nutrition. Nick is especially interested in how science and empiricism benefit subjective human experience, from personal wellness to the health of communities.

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