Krill Oil: Omega-3 in Phospholipids vs. Fish Oil

In the world of omega-3 supplements, fish oil has dominated for decades. But in recent years, a new, more expensive competitor has emerged claiming to do the same job, and even better: krill oil. Its red-orange capsules, labels promising improved absorption and a natural antioxidant, and the "clean" branding of a tiny marine creature from the Southern Ocean, have all made it one of the most talked-about supplements in the field.

But behind the marketing promise lies a simple question: Is krill oil truly superior to fish oil, or are you paying more for the same thing in a prettier package? In this article, we will break down the claims one by one. We will explain the structural difference between the phospholipid form of krill oil and the triglyceride form of fish oil, what astaxanthin does, and what the studies, especially the key study by Ulven and colleagues, actually showed. The spoiler: krill oil is a legitimate and good source of omega-3, but the marketing sells the "better absorption" far beyond what the evidence supports. That is why we rated it yellow.

What is Krill Oil?

Krill oil is extracted from Antarctic krill (Euphausia superba), a tiny marine crustacean a few centimeters in size that lives in massive swarms in the waters of the Southern Ocean and serves as a staple food for whales, penguins, and fish. Here is what is important to understand about it:

• It provides EPA and DHA. Just like fish oil, krill oil contains the two active and important omega-3 fatty acids, EPA and DHA, in their ready-to-use form.
• Its omega-3 is bound to phospholipids. This is the key structural difference. In fish oil, most EPA and DHA are bound to triglycerides, whereas in krill oil, a significant portion, over 80 percent according to some sources, is bound to phospholipids, the same fat molecules that make up our cell membranes.
• It contains natural astaxanthin. This is an antioxidant from the carotenoid group that colors krill and krill oil red-orange. It is naturally present in krill oil but not in regular fish oil, and it provides some stability against oxidation.
• It contains less omega-3 per capsule. The concentration of EPA and DHA in krill oil is often lower than in concentrated fish oil, so sometimes more capsules are needed to reach the same amount of omega-3.

Krill oil is significantly more expensive than standard fish oil per gram of omega-3, and this is one of the key factors in the decision. The real question is whether the structural difference, the phospholipids and astaxanthin, justifies the price gap.

Phospholipids vs. Triglycerides: The Mechanism Behind the Claim

The main marketing claim of krill oil is better absorption, and to understand it, you need to understand the difference in the form of the fatty acids.

In fish oil, EPA and DHA are bound to a glycerol backbone in the form of triglycerides. This is the natural form of most fats in food, and the body knows how to break down and absorb it well. In some concentrated omega-3 preparations, the fatty acids are in ethyl ester form, a form that is absorbed slightly less well, but most quality fish oils today are in triglyceride form.

In krill oil, a large portion of EPA and DHA is bound to phospholipids. The theoretical rationale: phospholipids mix better with water and bile in the intestine, and therefore may be more accessible for absorption, and additionally, they are the form in which fatty acids are naturally incorporated into cell membranes. Hence the claim that krill oil is absorbed more efficiently and therefore a lower dose is sufficient.

This is a logical idea from a biochemical perspective, but there is a big gap between a theoretical mechanism and clinical proof. The only question that matters in the end is: does krill oil raise blood omega-3 levels significantly more than fish oil at an equivalent dose? Here, the evidence becomes much less conclusive than the marketing suggests.

The Current Evidence

Study 1: Ulven et al. 2011, Similar Effect at a Lower Dose

This is the most cited study in the context of krill oil, and even its title is revealing. In 2011, Ulven and colleagues published a randomized study in the journal Lipids titled "Metabolic Effects of Krill Oil are Essentially Similar to Those of Fish Oil but at Lower Dose of EPA and DHA, in Healthy Volunteers". The trial included 113 subjects with normal to slightly elevated cholesterol or triglycerides, divided into three groups: krill oil (3 grams per day, providing 543 mg EPA and DHA), fish oil (1.8 grams per day, providing 864 mg EPA and DHA), or no supplement, for 7 weeks.

The results are telling: Both groups showed a similar increase in plasma EPA and DHA levels and similar improvement in metabolic markers, even though the krill oil provided about 37 percent less omega-3 than the fish oil. In other words, less omega-3 from krill oil achieved a similar result. This is the best evidence that the phospholipid form is indeed effective, and that the body absorbs and utilizes omega-3 from krill oil well. But note the wording: essentially similar, not superior.

Study 2: Schuchardt et al. 2011, Trend Without Significance

Another notable study that directly examined the absorption question. In 2011, Schuchardt and colleagues published a crossover study in Lipids in Health and Disease comparing the incorporation of EPA and DHA into plasma phospholipids after taking krill oil, fish oil in triglyceride form, and fish oil in ethyl ester form, all at a dose of 1680 mg EPA and DHA, in 12 healthy young men.

Krill oil did show the highest incorporation into plasma phospholipids over 72 hours, followed by the triglyceride form and then the ethyl ester. However, the researchers explicitly noted that due to large standard deviations, the differences between the three forms were not statistically significant for DHA and for total EPA and DHA. That is, a trend in favor of krill oil, but not a definitive proof of superiority. Additional studies on the topic have given mixed results, and some have found no absorption advantage for krill oil at all.

Study 3: Reviews and Meta-Analyses, The Balancing Picture

When looking at the entire body of research, rather than a single study, the picture becomes clearer. A 2014 review that re-examined the bioavailability studies of krill oil reached a critical conclusion: none of the studies convincingly showed a real improvement in the absorption of omega-3 fatty acids from krill oil compared to fish oil, partly due to small sample sizes and methodological issues.

More recent meta-analyses indicate that krill oil does raise the omega-3 index in the blood, and sometimes appears slightly more efficient per gram, but the gap is not dramatic and the actual clinical effects, on the heart, triglycerides, and inflammation, are similar to those of fish oil. The bottom line of the literature: krill oil is an effective and legitimate source of omega-3, but the claim that it is "much better absorbed" or "clinically superior" to fish oil is simply not well-supported by the evidence.

What About Astaxanthin?

One advantage krill oil has that regular fish oil does not is astaxanthin, the natural antioxidant that gives it its red color. Astaxanthin is a powerful carotenoid, and it contributes to the stability of krill oil against oxidation, meaning it is less prone to going rancid and developing a fishy taste. This is a real practical advantage.

But it is important to keep perspective. The amount of astaxanthin in krill oil is very small, usually less than 1 mg per serving, far below the doses tested in studies on astaxanthin as a standalone supplement. Therefore, although astaxanthin preserves the oil itself, there is no evidence that this tiny amount provides significant independent health benefits. Anyone interested in astaxanthin as an antioxidant for skin or eyes would get a relevant dose only from a dedicated astaxanthin supplement, not from krill oil. In other words, astaxanthin is more of a manufacturing advantage (stability) than a direct health benefit.

Should You Take Krill Oil?

We rated krill oil yellow, not green, and not because it doesn't work, but because its marketing promises more than the science delivers, and the price is high. Here are the balancing considerations:

• It is indeed an effective source of omega-3. The Ulven study showed it raises blood omega-3 like fish oil, even at a lower EPA and DHA dose. It is not an empty supplement.
• But clinical superiority has not been proven. There is no good evidence that it is superior to quality, cheap fish oil in terms of actual health outcomes.
• It is significantly more expensive. Per gram of omega-3, krill oil is much more expensive than fish oil. If the goal is simply to raise omega-3, fish oil in triglyceride form offers much better value for money.
• It contains less omega-3 per capsule. You may need more capsules to reach an effective dose, further increasing the cost.
• Real practical advantages. There is almost no fishy taste and fewer fishy burps, thanks to the astaxanthin stabilizing the oil. For those to whom this matters, it is a legitimate consideration.

Beyond the rating, there are some important safety points. Like any omega-3 source, krill oil has a mild blood-thinning effect, a slight slowing of clotting, so anyone taking anticoagulant medications like warfarin, or antiplatelet drugs like aspirin on a regular basis, or about to undergo surgery, should consult a doctor before taking it. Another critical point: krill oil is derived from a marine crustacean, so it is prohibited for anyone with a shellfish allergy, which can be severe. Additionally, there is a real sustainability issue: krill fishing in the Southern Ocean raises environmental concerns because krill is the base of the food chain for whales, penguins, and fish. Those concerned about this may prefer fish oil from a sustainable source, or vegan algae oil. Finally, pregnant and breastfeeding women and people with chronic medical conditions should consult a doctor regarding the appropriate dose and type.

What to Take Away from the Research?

1. Krill oil is a legitimate choice, but not magic. If you want to take it and have the budget, it is an effective source of omega-3. Just don't expect a dramatic advantage over fish oil.
2. If the goal is value for money, fish oil in triglyceride form wins. It is cheaper, more researched, and raises omega-3 just as well, simply at a slightly higher dose.
3. If you suffer from fishy taste and burps, krill oil may be more comfortable. The astaxanthin stabilizes the oil and reduces the oxidation that causes the aftertaste.
4. If you have a shellfish allergy, avoid it completely. Krill oil is derived from a marine crustacean and this is an absolute contraindication. In that case, fish oil or algae oil are the solution.
5. Aim for levels, not just dose. If you take omega-3 seriously, from any source, you can check your blood omega-3 index with a test and adjust the dose accordingly.

For those who want to try it, you can purchase krill oil on iHerb in various dosages. To check which supplements are suitable for your health goals, including heart health, based on your age and condition, you can use our personal supplement checker that rates each supplement according to the quality of evidence. For those interested in alternatives, we also recommend reading our guide on omega-3 and fish oil and on vegan algae oil.

The Broader Perspective

Krill oil is an excellent case study in how we look at supplements: it is not enough that a molecule works; we must ask whether it works better than what already exists, and how much it costs us. Krill oil does raise blood omega-3, and its phospholipid form is biochemically elegant. But between a promising mechanism and proven clinical advantage lies a large gap, and in the case of krill oil, that gap is filled more with marketing than with evidence.

The practical lesson is twofold. First, omega-3 (EPA and DHA) is one of the most important dietary components for heart, brain, and eye health, and any quality source that raises blood omega-3 levels, whether fish oil, krill oil, or algae oil, fulfills the role. The choice between them is a matter of budget, preferences, and values (taste, allergies, sustainability), not a matter of "which is the magic omega-3." Second, and this is the perspective we always hold: when a supplement works but the marketing inflates its advantage, our job is to tell the full truth, both the good and the qualified. Krill oil is a good supplement, just not the miracle promised on the package. And that is exactly the difference between a green rating and a yellow rating.

References:
Ulven SM. et al., Metabolic Effects of Krill Oil are Essentially Similar to Those of Fish Oil but at Lower Dose of EPA and DHA, in Healthy Volunteers, Lipids, 2011;46(1):37-46 (DOI: 10.1007/s11745-010-3490-4)
Schuchardt JP. et al., Incorporation of EPA and DHA into plasma phospholipids in response to different omega-3 fatty acid formulations: a comparative bioavailability study of fish oil vs. krill oil, Lipids in Health and Disease, 2011;10:145 (DOI: 10.1186/1476-511X-10-145)
Salem N, Kuratko CN., A reexamination of krill oil bioavailability studies, Lipids in Health and Disease, 2014;13:137