Fish Oil: Friend or Foe?

Apr 16, 2019

Do the risks of consuming rancid fish oil outweigh the health benefits?

When delving into the subject of fish oil I discovered a rabbit hole as deep as the ocean.  At the very least, it is understood that in fish oil there are significant nutrients that our bodies need otherwise there wouldn’t be such a massive discussion on the subject.  People are clearly catching on to the value of this product for our health because fish oil supplement sales in the U.S. alone exceed one billion dollars annually.

The varieties of fish oils, the sourcing, the processing methods and the dosage are the main topics that bring cloudiness to the overall question: at the end of the day, do the benefits outweigh the harm?

To give you my basic conclusion first, if you aren’t going to get the highest quality fish oil possible and store it properly, then you’re better off not taking it.  This is not a case of “some is better than none.”  A low quality fish oil full of toxic components or that has been spoiled by oxidation would be worse for you than taking none at all, especially when there are ways you can obtain these beneficial nutrients through whole food sources.


What’s in fish oil that’s so great?

Omega 3s

There are two primary nutrients that make fish oil liquid gold: the Omega 3 fatty acids EPA and DHA and the fat-soluble vitamins A and D

The Omega-3s EPA (eicosapentaenoic acid) and DHA (docosahexaenoic acid) are not produced in the body and can only be found in marine sources.  These fish-derived fatty acids have been associated with:

  • Ideal fetal and child development especially for eyesight and the brain
  • Improved cardiovascular function and fewer coronary events by reducing vascular inflammation
  • Improved immune function and reduction of inflammatory biomarkers
  • Neuroprotective benefits including healthy aging and prevention of Alzheimer’s Disease

Omega 3s are key components of cell membranes throughout the body and especially in the brain and retina.  The plant-derived Omega 3 ALA (alphalinoleic acid), found in flax, chia and hemp seeds, can be converted to EPA and DHA by the enzymes enlongase and desaturase, but research shows that only a small amount of EPA and DHA can be synthesized from ALA by this process.  One study found that the ALA conversion to EPA was around 7% while the conversion to DHA, arguably the more essential of the two, was only 0.013%. In addition, it has been shown that high insulin levels can impair the production of the enzyme desaturase.  So for those who are on a carbohydrate-based diet, this will further reduce the conversion rate.  Therefore, solely plant-based diets will not be providing the body with an adequate amount of these essential fatty acids for optimal health.

There are countless studies to show the positive effects from women supplementing with EPA and DHA during pregnancy including the child’s improved hand-eye coordination skills as well as a reduced occurrence of allergies possibly due to lower levels of the cells associated with inflammation and immune response.

Fat-Soluble Vitamins

"What does it mean for a vitamin to be fat-soluble?  I thought vitamins were those chewy, Flintstones shaped candies my mother used to give me."

The vitamins include A, D, E and K are fat-soluble which means that they are absorbed in the intestines along with the presence of dietary fats and are stored in the body’s fatty tissue.  These micronutrients are required in small amounts (as opposed to macronutrients which are needed in much larger amount) for a diverse array of biological functions.  “Over the past two decades, deficiencies of these vitamins have been associated with increased risk of cancer, type II diabetes mellitus and a number of immune system disorders.”2

Benefits of Vitamin A (also known as retinol):
  • Healthy vision particularly in dim light
  • Embryonic Stem Cell development
  • Healthy structure of Epithelial cells like those found in the lining of the gut
  • Regulation of macronutrient metabolism
  • Inhibits growth of tumor cells

Vitamin A also plays a key role in the immune system since it maintains healthy Epithelial cells which are found in the skin, gut, respiratory system and genitals - all of those barriers which provide the first line of defense against infection.  Communities that are prone to Vitamin A deficiency may have a higher rate of infectious diseases. In plant sources, Vitamin A is often found in pigmented veggies and fruits like carrots or sweet potatoes. Animal sources include certain types of fish and things like beef liver.

Benefits of Vitamin D:
  • Proper immune function and prevention of autoimmune disorders
  • Bone health by way of calcium homeostasis
  • Stimulates Insulin secretion

Vitamin D deficiencies are commonly linked to rickets in children and softening of the bones in adults and low vitamin D blood levels are commonly found in communities with immune-compromised conditions like HIV.  Oddly enough, even in areas where there is sunlight year round, deficiencies have still been noted, illustrating that this is still a nutritional deficiency.

Fun fact:
Vitamin D therapy has been used in the past to treat Tuberculosis because of its ability to stimulate the formation of a natural antibiotic in white blood cells through regulating gene transcription.  Despite its proven efficacy and TB still being a worldwide epidemic, Vitamin D therapy has not been used commonly to treat TB since the 1940s and as early as the 1800s through phototherapy, sunlight therapy, cod liver oil supplementation and Vitamin D injections.

Vitamins A and D are the primary fat-soluble vitamins found in fatty fish and fish oils and new research is being done on not simply the individual importance of these two vitamins, but the relationship between the two and their role in gene expression.  As with many aspects of nutrition, there is still so much that isn’t fully understood about either the individual or synergistic relationship between these two micronutrients.

Couldn’t I get these nutrients from food?

Yes, supplementing with fish oil isn’t a necessity if you are getting adequate amount of EPA, DHA and Vitamins A & D from food.  Even if you are eating the 2 cups of carrots per day in place of one serving of Cod Liver Oil, you still won't be absorbing a sufficient amount of Vitamin A. 

"Vitamin A is approximately 20 times more bio-available in animal-based food than plant foods.  In fact, plant foods don’t actually have any vitamin A. They have carotenoids which have to be converted to Vitamin A."3

Let’s take a look at some of the foods you would need to eat in absence of supplementing with fish oil.

For Omega 3s

  • Pastured egg yolks
  • Pasture raised animal products
  • Pastured butter
  • Fatty fish (wild-caught is preferable due to the fish’s diet in the wild)

Amount of Omega 3s found in different types of fish based on 3.5oz serving (keep in mind these numbers include ALA as well)

  • Mackerel (5134mg)

  • Salmon (2260mg)
  • Herring (1729mg)
  • Oysters (672)
  • Sardines (1480mg)
  • Anchovies (2113mg)
  • Caviar (1086mg per 1 Tbsp)

Vitamin A

  • Beef liver 3oz 6582 mcg
  • Sweet potato, whole 1400 mcg
  • Carrots 459 mcg ½ Cup
  • Whole egg 70 mcg
  • Spinach 573 mcg 

Vitamin D

  • Salmon 450 IUs 3oz
  • Swordfish 566 IUs 3oz
  • Canned Tuna fish 154 IUs 3oz
  • 1 Egg yolk 41 IUs
  • Beef liver 41 IUs 3oz
  • 2 Sardines 40 IUs
  • Fortified milk or yogurt or OJ 115 IUs per cup
Cod Liver Oil - 1 Tbsp   
  • Omega 3s 2664mg
  • Vit D 1360 IUs
  • Vit A 1350 mcg  (or 4500 IUs)


Not all fish oil is created equal

Now that you’ve seen the benefits of the nutrients in marine-derived products, let’s touch on the varieties of fish oil supplements out there.  It seems like health pros we come across will advocate strongly for one over another type of supplement and although I have my personal preference, I’m not really here to debate the subject of which is the best variety (although if I have to vote - this would be my vote), but rather illustrate how quality differs between the production methods.

Fish Oil

From the body of oily fish like anchovies, salmon, sardines, mackerel

Main argument for:

  • More sustainable food source

Main argument against:

  • High rate of toxins from fish and high potential oxidation levels due to processing methods
  • Nutrients are less bioavailable
  • Not as high in Vitamins A & D

Vital Choice Wild Alaskan Salmon Oil

Cod Liver Oil

From the livers of cod

Main argument for:

  • High in Vitamin A & D

Main argument against:

  • High possibility of toxins like heavy metals due to build up in the fish’s liver

Green Pastures Fermented Cod Liver Oil
Rositas Extra Virgin Cod Liver Oil

Krill Oil

Made from Shrimp-like creatures in Antarctica and naturally contains astaxanthin (makes the red color like in crab, lobster, salmon and red trout)

Main argument for:

  • High bioavailability 
  • low oxidation level due to naturally occurring astaxanthin
  • (fun fact - protects your skin against sunburn)

Main argument against:

  • Possible over-fishing leading to damaging effect on Antarctic ecosystem
  • Low levels of Omega 3s (although it is more bioavailable so this may not be a concern)

Viva Naturals Antarctic Krill Oil

The dangers of buying low quality oil

Not only do you get variety when it comes to the type of fish the oil is made from but also in the quality of the processing method.  The biggest downside in consuming low quality fish oil is in the high likelihood that oxidation has occurred. Oxidation of an oil happens when it is exposed to light, heat or oxygen.  At the molecular level, this means that the removal of an electron from the chain makes an unstable molecule. Nature loves balance and when an electron is removed, the fatty acid will try to restore this balance by stealing an electron from other molecules like from DNA or cell membranes.  This forms what are known as Radical Oxygen Species or “free radicals” to form in the body which are known to be linked to increased inflammation, risk of heart attack, cancer and stroke. Ever here of how “antioxidant rich foods” help prevent cancer?  That’s because it is thought that these antioxidants will scrub the body of free radicals that form from oxidation.

Sounds scary, right?  Well, it’s not a death sentence, but many Americans already have a diet high in these oils that have been oxidized like canola oil which is used for frying at most restaurants, the oils in nuts that have gone rancid or other things like ground flaxseed which sits at room temperature.  With these free radicals being so commonly linked to disease, then it becomes important to mitigate our consumption as much as possible.

In several studies in the U.S. and Canada, as much as 50% of the brands of fish oil were above safety recommendations for oxidation levels, some were as high as twice the limit.  When you consider the long process a fish must undergo to be captured, shipped great distances, stored, sold, processed then bottled and purchased by you, it’s not surprising that much of the fish oil supplements on our shelves have high levels of oxidation.  Many oils don’t start off intended for ingestion and so securing high quality fish from clear waters or storing the crude fish oil to minimize oxidation is not a concern early on in the manufacturing process. One study elaborates:

“Each catch is transported on a fishing vessel to shore, where it is then processed by fractionation into fish meal and crude fish oil. The oil produced is stored in large tanks before being shipped on for further refining, particularly to China. This refining process typically involves several steps, notably including repeated heating at high temperatures. The last stage of refinement is deodorisation to remove NEFA, aldehydes and ketones, which are responsible for the undesirable taste and rancidity of oxidised oils.  Less than 25 % of the total crude fish oil supply is destined for human consumption and undergoes additional refinement and deodorisation. The remainder is predominantly used in the aquaculture industries. As a result, fish oil supplements are just one small part of an international commodity trade, where early steps in processing are not specific for supplement production and the catch, isolation, purification and manufacture of oil all occur well removed from the final consumer market.”1

At each stage in the life of the fish oil, there is a new opportunity for oxidation.  Exposure to air and light as well as heating process not only causes harmful oxidation, but also kills the delicate fat-soluble vitamins.  Many fish oils will have added antioxidants - compounds that combat the oxidation process - like Vitamin E oil or rosemary oil for example.  And as we saw earlier, products like Krill Oil have the naturally occurring antioxidant astaxanthin.

Aside from oxidation that can and will most likely occur during processing, the sourcing of the fish is an inherent concern particularly from older fish that are higher on the food chain and have had time to accrue toxic compounds like:

PCBs (used in Pre-1979 industry)
Dioxin (a highly toxic manufacturing byproduct)
PCPs (pesticide)
Radioactive Strontium
Toxic metals like cadmium, lead, chromium and arsenic (
Heavy metals can cause nervous system dysfunction, blindness, cancer, irreversible liver and kidney damage

Putting it into action

There are many companies that value the quality of the fish oil both in terms of the type of fish used as well as the processing method and storage of the delicate product.  Here are some tips for you to look out for when purchasing your own fish oil supplements.

  • Buy in amber glass bottles (plastic lets light in)
  • Refrigerate and buy small amounts to ensure use before oxidizes
  • Buy directly from manufacturer instead of grocery store shelf to ensure freshness
  • High price usually = better quality
  • Look for added antioxidants like Vit E oil, astaxanthin
  • Educate yourself on the best and most respected brands

As with any macro- and micronutrients, whole food is the most ideal source as opposed to supplementation.  If we were all dialed-in with our nutrition enough to eat pasture-raised butter, whole eggs, beef liver and wild-caught fish a few times a week, then supplementing with some form of fish oil wouldn’t be needed. Delivered to us in the form of whole foods, these nutrients would arrive intact with optimal bioavailability.  But with modern diets leaning more in the direction of convenience, then taking a fish oil supplement daily is a convenient way to ensure we are getting the nutrients we need to thrive and prevent disease...that is, assuming you get your hands on fresh and high quality fish oil.  So, next time you reach for your fish oil, ask yourself how old it is and if it may simply be better to have some liver or sardines instead.

A note for our furry friends:
Fish oil is a common added ingredient in pet food.  Are you storing your dog’s kibble at room temperature for weeks upon weeks?  You might want to reconsider securing it in an air-tight, food safe and dark container and storing it somewhere cool.  Our pets are just as susceptible to this harmful oxidation process and each time you open that bag of food, there may be oxidative damage occurring.







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