Fish oil or krill oil; that is the omega-3 question of the decade. Fish oil certainly has a long history with a plethora of research to validate its health benefits, but suddenly krill oil moves into the neighborhood making claims of superiority and seeming ready to displace the position fish oil has occupied for so long. Many of us consciously or subconsciously operate under the idea that newer is better, which may cause us to side with krill oil, but this philosophy doesn’t always hold water. Maybe the question is not an either/or scenario, but rather, what are the strengths and limitations of each that may warrant the use of both.

The Argument

The argument for choosing either fish oil or krill oil is rooted in studies that suggest krill oil may be more effective at building tissue levels of omega-3 polyunsaturated fatty acids (n-3 PUFA). This conclusion stems from the fact that up to 65 percent of the omega-3 PUFAs in krill oil are esterified as phospholipids (PL) rather than triacylglycerols (TAG), which are the exclusive form found in fish oil. Phospholipids are generally considered to have a higher bioavailability, being the main component of cell membranes, and are more efficiently absorbed by brain tissue, especially.

The Truth About Bioavailability

Even though logic suggests the bioavailability of phospholipid-based omega-3 PUFAs is better than the traditional TAG form, the proof is always in the studies.

This logic was put to the test in an animal study and the results were published earlier this year (2019). Mice were fed either a control diet or one of six DHA (1%, 2%, or 4%) as PL-DHA or TAG-DHA diets for 4 weeks. Both the PL-DHA and TAG-DHA diets resulted in higher DHA concentration in liver, adipose, heart, and eye, but not brain tissue.  However, there was no significant difference in DHA concentration in all tissues between the PL- or TAG-DHA forms. Additionally, all tissue types showed higher levels of EPA PUFAs for both PL-DHA and TAG-DHA diets. According to this study, the PL form of omega-3 PUFAs doesn’t seem to increase DHA and EPA any more significantly than the TAG form.

In another animal study, published in 2018, researchers investigated the effect of oral short-term and long-term administration of krill oil and fish oil on bioavailability in the blood and brain of rats. Rats were given 1000mg of either fish oil, krill oil made by enzyme extraction, krill oil made by solvent extraction, or control. Blood and brain samples were collected after 2, 4, 8, 12, 24, 48 h of oral administration. Rats were then given 500mg daily for 2 weeks of the same test oils or control and then blood and brain samples collected for long-term evaluation. Results showed that PUFA content in the brain was higher in the short-term among rats receiving krill oils. In the long-term, there was a slightly greater level of EPA and DHA in the brains of rats receiving krill oils compared to fish oil, but the difference was not significant. In the long-term, there was no significant difference between blood levels of DHA among rats receiving either krill or fish oils, but those receiving fish oil did show slightly higher blood concentrations of EPA.

Other Metabolic Markers

What about the effects of krill oil or fish oil on metabolic markers such as fasting serum TAG levels, total lipids, phospholipids, cholesterol, cholesteryl esters, non-esterified cholesterol, vitamin D, and fasting glucose? According to an 8-week randomized parallel study of thirty-six healthy subjects aged 18 to 70 years receiving either fish, krill oil or control oil, fasting serum TAG did not change between the groups, blood glucose decreased significantly in the krill group, vitamin D increased significantly in the fish group, and all other markers increased significantly in the krill oil group.

The Benefits of Krill Oil

Krill is distinct from fish oil not only because of its higher phospholipid content, but also because it contains a unique antioxidant profile which includes the powerful antioxidant, astaxanthin. Astaxanthin has been shown to impart significant health benefits on eyes and skin, but also possesses anticancer, antidiabetic, anti-inflammatory, and antioxidant activities. Krill oil also offers a more sustainable form of PUFAs, coming from a large stock of Antarctic crustaceans with a much higher reproduction rate compared to cold-water fish.

The Benefits of Fish Oil

Fish oil still boasts of significantly higher levels of both EPA and DHA, compared to krill oil and although advocates of krill oil argue that bioavailability is better, studies aren’t showing a significant difference, meaning fish oil may still be a superior means of raising the concentrations of these PUFAs. Fish oil can also be easily obtained in clinically relevant doses by consuming cold-water fish. In this way, consumers are also reaping the benefits of other nutrients found in fish including iodine, selenium, taurine, high-quality proteins, and vitamins D and B₁₂. And due to its wide availability, fish oil remains more cost-effective.

Despite being apparent rivals, krill and fish oil may not be mutually exclusive after all. Instead, each may play a role the other cannot fulfill, making their combined use beneficial and even preferred.