Krill Oil vs Fish Oil: What Three Small Trials Found

The two oils carry the same omega-3 fats in different molecules, and a few small trials have tested how much of each reaches the blood.

Omega-3 fats are building blocks of cell membranes.* The two best known are EPA and DHA, short for eicosapentaenoic acid and docosahexaenoic acid.

Fish oil usually carries them as triglycerides or ethyl esters, which are two chemical forms of fat. The NIH's National Center for Complementary and Integrative Health states that krill oil contains omega-3s in the form of phospholipids^[5]. Phospholipids are the same type of fat that cell membranes are made of.

Krill is a small marine crustacean, and its oil also comes with astaxanthin, a red pigment and natural antioxidant. The trials below compared how much EPA and DHA showed up in the blood after each oil.

For reference, our omega-3 has 1000 mg of krill oil per softgel, with astaxanthin.

This trial gave one dose, then tracked EPA and DHA in blood plasma phospholipids for 72 hours. The score is the area under the curve, which adds up how much arrived over time.

Who took part: 15 healthy adults completed all three periods in this crossover trial^[3].

Dose used: About 1,700 mg of total omega-3 fats per treatment. EPA plus DHA came to about 1,400 mg from krill oil, 1,102 mg from krill meal and 1,455 mg from fish oil.

What changed: Krill oil scored 89.08, against 59.15 for fish oil (p = 0.003) and 44.97 for krill meal. Krill oil came out about 1.5 times higher than fish oil, even though its EPA plus DHA dose was slightly lower.

The catch: The krill oil arm took 16 capsules against 10 for fish oil. The krill meal arm received the least EPA plus DHA. A krill oil producer sponsored the trial, though the authors say the sponsor had no role in analyzing the data.

Krill meal and fish oil did not differ. The authors wrote that this "argues against the interpretation that phospholipids are better absorbed than triglycerides."

They suggested that the food matrix, meaning what the fat is packaged in, seems responsible for the differences. In other words, the krill oil as a whole performed well, and the packaging of the fat may matter as much as the chemical form.

For a reader, this is a useful distinction. The trial supports krill oil as a finished product. It does not show that phospholipids alone explain the result.

This small double-blind crossover trial used the same 72-hour method as the 2015 study.

Who took part: 12 healthy young men in a 2011 trial.

Dose used: 1,680 mg of EPA plus DHA per treatment, from re-esterified triglyceride fish oil, ethyl ester fish oil or krill oil.

What changed: Krill oil scored 80.03, triglyceride fish oil 59.78 and ethyl ester fish oil 47.53. Krill oil ranked first with an equal EPA plus DHA dose.

The catch: People varied a lot, so differences for DHA and for EPA plus DHA combined were not significant. The EPA difference was a trend (p = 0.057). The krill oil also held 22% of its EPA and 21% of its DHA as free fatty acids, which the authors said should be investigated further.

The omega-3 index is the share of EPA and DHA in red blood cell membranes. It reflects intake over weeks, so it is a steadier measure than a single blood draw.

Who took part: 24 healthy adults in a 2013 randomized, double-blind crossover trial^[1]. Everyone took krill oil, fish oil and a corn oil placebo, each for 4 weeks.

What changed: The omega-3 index rose about 1.04% with krill oil and 0.47% with fish oil. Only the krill oil supplied astaxanthin.

The catch: A 2014 commentary called the trial's conclusions "not justified and misleading." Its authors said the fish oil was not typical of fish oil on the market, with about 32% linoleic acid, an omega-6 fat.

They also noted EPA plus DHA intake of 778 mg per day for krill and 664 mg for fish oil. They said the trial would need to be repeated with a standard fish oil. For that reason, the 2013 index gain is best read as a lead, not as proof of a two-fold advantage.

In the two trials that matched or lowered the krill oil dose of EPA plus DHA, krill oil scored higher than fish oil. That held for the 2015 result (89.08 against 59.15) and for the 2011 result (80.03 against 59.78 and 47.53). No trial showed krill oil scoring lower.

The 2015 authors credit the food matrix, and krill oil is a food-based oil with its own phospholipids and astaxanthin. So the practical point is that krill oil delivers EPA and DHA to the blood at least as well as fish oil.

Side effects of omega-3 supplements in general are usually mild^[5]. NCCIH lists unpleasant taste, bad breath, headache, heartburn, nausea and diarrhea.

The takeaway: krill oil is a well-supported way to add omega-3 to your diet. It raised blood EPA and DHA at least as well as fish oil in small trials, and it brings its own astaxanthin. The omega-3 form is worth weighing along with the milligrams printed on a label.

Krill is a crustacean, so krill oil is a shellfish product. It is not for people with a shellfish or seafood allergy. A krill oil softgel may also use gelatin, so check the label if you avoid animal products.

Omega-3 supplements may affect bleeding. The Harvard Nutrition Source^[6] says they may raise the risk of bleeding and advises telling your doctor, especially if you use blood thinners.

Check with your doctor first if you:

• Have a shellfish or seafood allergy
• Take warfarin, aspirin or another medication that affects clotting
• Are pregnant or breastfeeding
• Are choosing omega-3 for a child
• Have a health condition or a planned surgery

The Harvard page reports that the FDA says supplement labels should not recommend more than 2000 mg of EPA and DHA per day.