Krill Oil vs Fish Oil vs Cod Liver Oil: What's the Difference?

 

The Lowdown on Krill Oil and Fish Oil: Which Omega-3 Supplement Should You Choose?

If you've been following my site, you're probably aware that I recommend consuming fish in moderation, and eating certain types that are less likely to be contaminated with mercury. Fish, despite its high levels of DHA and EPA omega-3 fatty acids, is now one of the most polluted foods today.

The National Resources Defense Council reports that predatory fish, such as large tuna, swordfish, shark, and mackerel, can have dangerous mercury concentrations in their bodies that are 10,000 times higher than those of their surrounding habitat.

Mercury works its way up the food chain, as large fish consume contaminated smaller fish. And Instead of dissolving or breaking down, mercury accumulates at ever-increasing levels.i

I sincerely believe that in order to stay safe from mercury, you must avoid regular fish consumption. I do highly recommend high-quality Alaskan wild salmon that is certified to be low or free of contaminants (including mercury) – but you should still eat this fish in moderation.

However, you must make sure to get enough omega-3s even without consuming fish. One supplement that many people opt for is fish oil, a product extracted from oily, deep-ocean-farmed or wild-caught fish. But is fish oil really as safe and environment-friendly as manufacturers claim? Or does this supplement only add to the toxic burden inside your body?  

Krill Oil Shows a Clear Edge Over Fish Oil in Absorption 

A 2024 study published in Food Chemistry: X showed clear differences in absorption depending on both the omega-3 source and formulation. Understanding these differences directly affects the benefits you feel in your heart, brain, joints, and beyond.

For the Food Chemistry: X study, researchers analyzed 26 high-quality randomized controlled trials with data collected between 2003 and 2023.2 The goal was to compare how well your body absorbs omega-3 fats from different sources — fish oil and krill oil.

Researchers focused on key markers in the blood, such as the omega-3 index, maximum blood concentration, time to reach peak levels, and the total exposure over time. These are standard ways scientists measure how efficiently nutrients get into your system and how long they stay there.

• Krill oil raised omega-3s more at lower doses — The findings showed that krill oil was more effective than fish oil at raising blood omega-3 levels when given at lower doses, while fish oil needed higher amounts to achieve a similar effect. When dosages were under 2,000 milligrams (mg), krill oil consistently outperformed fish oil. This means if you take krill oil, you could use a smaller dose and still improve your omega-3 status. Fish oil required higher intakes — sometimes above 3,000 mg — to move the omega-3 index upward in a meaningful way. The omega-3 index is the percentage of EPA and DHA in your red blood cell membranes, and higher scores are strongly linked to better heart and brain outcomes.
• Fish oil emulsions delivered strong short-term results but come with a downside — While standard fish oil capsules lagged behind krill oil, emulsified forms of fish oil were an exception. Emulsions are blends where the oil is broken into tiny droplets, making it easier for your digestive system to process. These emulsions increased peak blood concentrations of omega-3s more than either regular fish oil or krill oil, meaning your body gets a faster boost. Fish oil emulsions do carry some downsides, however, and rancidity is one of the main concerns. Because emulsions mix oil with water to improve absorption, they have a much larger surface area exposed to oxygen compared to standard capsules. That makes them more vulnerable to oxidation, the chemical reaction that turns fats rancid. When fish oil oxidizes, it produces harmful byproducts that increase inflammation instead of reducing it — the exact opposite of what you want from omega-3s.
• High-dose fish oil improved long-term levels but with serious trade-offs — Fish oil above 3,000 mg per day raised the omega-3 index more strongly than lower doses. However, the researchers cautioned that higher intakes also raised the risk of unpleasant side effects, including digestive upset and excessive blood thinning. High doses of omega-3s, especially from supplements, have also been linked to an increased risk of atrial fibrillation, a serious heart rhythm problem.3 This means that while high-dose fish oil works, it comes with a price. Krill oil at lower doses delivered a safer path to similar benefits without forcing your body to handle such a heavy load.
• Krill oil phospholipids gave it a unique advantage — The key reason krill oil worked better at lower doses was its structure. In krill oil, omega-3s are attached to phospholipids, a type of fat that naturally makes up your cell membranes. Because your cells are already built from phospholipids, this form of omega-3 slips in more easily.

The researchers explained that phospholipids in krill oil have amphiphilic properties, meaning they dissolve well in both water and fat. This makes them more compatible with your digestive system and easier to transport into your bloodstream. Fish oil, by contrast, usually contains triglycerides or ethyl esters, which are less efficient because they require pancreatic enzymes and bile acids to be broken apart before absorption. That extra step slows absorption and reduces efficiency.

The Truth About Fish Oil Supplements: Are You Consuming a Rancid Product?

I used to recommend taking a high-quality fish oil to enhance your intake of omega-3 fats. But eventually, I found a better solution. Fish oil is highly perishable because it lacks antioxidants. When fish oil turns rancid inside your body, it leads to free radical formation.

This is a major drawback of fish oil – as you increase your intake of omega-3 fats from fish oil consumption, you also increase your need for antioxidant protection.

What's more, fish oil is often extracted from large, oily fish  – the same species that have high levels of methylmercury.

So even if you choose fish oil over fish, you are still at risk of mercury contamination.

The Environmental Effects of Overharvesting Fish

Fish oil may seem like a sustainable omega-3 source, but the truth is that it actually contributes to overharvesting – in fact, populations of top predator fish are disappearing at an alarming rate.

Ninety percent of large fish species consumed by humans and used for fish oil production, such as swordfish, tuna, cod, halibut, skate, marlin, and flounder, have been fished out since the advent of large scale industrial fishing in the 1950s. The depleting populations of these fish  may cause a shift in the entire ocean ecosystem.

What's more, fish farming, which produces the majority of fish oil supplements, also severely affects the environment by polluting our oceans with large amounts of fish feed and fish waste.

Why Krill Oil Is a Smarter Choice Than Fish Oil

Krill oil comes from krill, a tiny shrimp-like creature that lives in the pristine waters of Antarctica. Krill feed on plankton floating on the ocean's surface.

Krill oil contains high amounts of beneficial omega-3 fats EPA and DHA. But what sets it apart from fish oil is that its omega-3 fats are in a much more absorbable form that's ready to be used by your body.

Here's another reason to choose krill oil: it's rich in antioxidants, meaning it will not become rancid inside your body and will not lead to free radical formation. One of the most powerful antioxidants in krill oil is astaxanthin, a unique marine-source flavonoid that bonds with EPA and DHA, making them more bioavailable.

Also, because krill is at the bottom of the food chain, it does not accumulate mercury, unlike large fish species.

Unlike krill oil — a superior source of omega-3 fats — fish oil lacks any phospholipids. Research is now confirming just how important the phospholipid component is when it comes to gleaning all the benefits you can from your omega-3 fats.

There Is NO Danger of Overharvesting Krill

Because krill makes up the diet of whales, seals, and other marine creatures, many people are concerned that consuming krill oil is equal to “stealing” the natural food of these animals.

But this is not true at all.

Krill is actually the largest biomass on Earth, so there is a very large stock of renewable krill for both natural predators and humans.

In addition, krill harvesting is one of the most well-regulated industries today. There is even a precautionary catch limit set to ensure that there will be no overharvesting.

These facts make it clear that if you're choosing between krill oil and fish oil, krill oil is the smarter and superior choice.

Learn More About Fish Oil and Krill Oil Through This Infographic

I have outlined the distinguishable characteristics of both krill and fish oil in my Fish Oil versus Krill Oil: The Cold, Hard Facts infographic (featured image above). Here, you will discover:

• The origins and nutritional content of krill oil and fish oil
• Why krill oil harvesting is safer and more sustainable
• How fish oil and krill oil production impact the environment

Hopefully, this informative infographic will help you decide which omega-3 supplement will suit you better.

A Word of Warning on Krill Oil and Fish Oil Supplements

Remember, though, that fish oil and krill oil are both not recommended for some people, such as those with a shellfish or seafood allergy. Those who have a blood coagulation disorder or are taking blood thinners should also refrain from taking these supplements.

Cod Liver Oil vs Fish Oil: What's the Difference?

Fish oil and cod liver oil are derived from different fish sources and have unique benefits. Fish oil is usually derived from fatty fish like herring, tuna, salmon and mackerels. Cod liver oil comes from the liver of codfish.

Both have omega-3 fatty acids, but cod liver oil has the added vitamins A and D. It’s safer to take only fish oil or cod liver oil, but not both. This is because cod liver oil contains very high amounts of vitamin A and vitamin D, thus taking too much could be toxic. For the purpose of treating arthritis, fish oil is the safer choice. However, if you want the added benefits of Vitamin A and D, cod liver oil may be a better choice.

The health benefits of both types of oil are their high levels of omega-3 fatty acids, which support many body functions and may prevent certain ailments. Our body can’t make Omega 3 on its own, which is why we need to get it externally.

These fatty acids are eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). These omega-3 fatty acids are the “good oils” that everyone needs to include in their diet.

Safety of Omega-3s

The IOM (Institute of Medicine) did not establish a UL (Tolerable Upper Intake Level) for any omega-3s, although it noted that high doses of DHA and/or EPA (900 mg/day of EPA plus 600 mg/day DHA or more for several weeks) might reduce immune function due to suppression of inflammatory responses. Doses of 2–15 g/day EPA and/or DHA might also increase bleeding time by reducing platelet aggregation.

We recommend taking a maximum of 1 gram of omega-3 per day. Higher amounts could be risky, because EPA and DHA are both polyunsaturated fats (PUFAs) and, like linoleic acid (LA), are susceptible to oxidation and the production of dangerous aldehyde metabolites.

Make sure you buy high-quality omega-3 fatty acid supplements, meaning that the omega-3 fatty acids are pure and have not oxidized much (having low “TOTOX” value).

However, according to the European Food Safety Authority, long-term consumption of EPA and DHA supplements at combined doses of up to about 5 g/day appears to be safe. It noted that these doses have not been shown to cause bleeding problems or affect immune function, glucose homeostasis, or lipid peroxidation. Similarly, the FDA has concluded that dietary supplements providing no more than 5 g/day EPA and DHA are safe when used as recommended. 

Two large clinical trials completed after these assessments found that taking 4 g/day of omega-3 supplements for several years slightly increased the risk of atrial fibrillation in people with CVD or at high risk of CVD. 

Some, but not all, large-scale randomized controlled trials (RCTs) investigating the effects of marine omega-3 fatty acids supplementation on cardiovascular outcomes have reported increased risks of atrial fibrillation (AF). The potential reasons for disparate findings may be dose-related.

In a Systematic Review and Meta-Analysis, published in Circulation 2021, 7 studies were included in the meta-analysis.

In RCTs examining cardiovascular outcomes, marine omega-3 supplementation was associated with an increased risk of AF. The risk appeared to be greater in trials testing >1 g/d.

Update: A 2024 study published in BMJ Medicine suggests that regular use of fish oil may contribute to atrial fibrillation and stroke among the general population.

Commonly reported side effects of omega-3 supplements are usually mild. These include unpleasant taste, bad breath, heartburn, nausea, gastrointestinal discomfort, diarrhea, headache, and odoriferous sweat.

The bottom line: always consult your healthcare provider before taking any type of supplement. 

Source and Reference: https://www.mercola.com/infographics/fish-oil-vs-krill-oil.htm

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