Krill oil and fish oil deliver the same two omega-3 fatty acids, EPA and DHA, but they differ in how well your body absorbs them, how much omega-3 you get per capsule, and what you’ll pay. Neither is universally “better.” Krill oil has an absorption advantage and comes with a built-in antioxidant, while fish oil packs more omega-3 per capsule at a fraction of the cost.
Why Krill Oil Absorbs Better
The core difference between these two supplements comes down to molecular packaging. In krill oil, EPA and DHA are bound to phospholipids, a type of fat that also makes up your cell membranes. In fish oil, those same omega-3s are bound to triglycerides. Because phospholipids mix more easily with your body’s own cell structures, krill oil’s omega-3s are believed to have higher bioavailability, meaning more of what you swallow actually reaches your bloodstream.
That said, the exact magnitude of this absorption advantage is still being pinned down. A crossover study in healthy adults compared a krill oil product containing 206 mg of EPA and DHA per gram to a phospholipid-enhanced fish oil with 337 mg per gram. Even with less omega-3 per capsule, krill oil consistently shows competitive blood levels of EPA and DHA in these head-to-head tests. The phospholipid structure appears to partially compensate for the lower concentration.
Omega-3 Content Per Capsule
This is where fish oil has a clear edge. A standard 1,000 mg fish oil capsule typically delivers 300 to 500 mg of combined EPA and DHA, depending on the brand and concentration. A krill oil capsule of the same size contains roughly 200 mg. That means you’d need to take more krill oil capsules to match the raw omega-3 dose of fish oil, which adds up in both pill count and cost.
For context, a clinical trial on mood used krill oil dosed at 520 mg of EPA and DHA daily, which required multiple capsules. The equivalent fish oil arm delivered 600 mg of EPA and DHA. If your goal is to hit a specific omega-3 target, fish oil gets you there with fewer pills.
The Antioxidant Advantage of Krill Oil
Krill oil contains astaxanthin, a reddish pigment that acts as a potent antioxidant. It’s also the compound that gives krill oil its distinctive red-orange color, compared to the yellow of most fish oil capsules. Krill oil additionally contains vitamins A and E.
Astaxanthin does two useful things. First, it protects the oil itself from going rancid, which is a common complaint with fish oil supplements that have been sitting on a shelf. Second, cell and animal studies suggest it has its own health benefits, including reduced oxidative stress. While human data on astaxanthin specifically from krill oil supplements is limited, it’s a genuine bonus that fish oil doesn’t offer.
Heart Health Effects
Both krill oil and fish oil lower triglycerides and support cardiovascular health. A systematic review of randomized controlled trials found that krill oil supplementation at doses under 3 grams per day decreased total cholesterol and triglycerides. Fish oil has decades of research behind it for the same outcomes, with well-established effects on triglyceride reduction at therapeutic doses.
The practical takeaway: if you’re taking omega-3s for heart health, both options work. Fish oil has a much larger body of clinical evidence simply because it’s been studied longer and in more trials. Krill oil’s results are promising but come from a smaller pool of research.
Purity and Contaminants
One concern people have with fish-derived supplements is mercury and other heavy metals. Krill sit near the bottom of the food chain, feeding on algae rather than other fish, so they accumulate very little contamination. Testing of commercial krill oil capsules found mercury levels below 0.2 micrograms per kilogram, with cadmium and lead also well under safety limits.
Fish oil isn’t necessarily dirty, though. Reputable fish oil manufacturers use molecular distillation to remove heavy metals and PCBs, and third-party tested products routinely meet strict purity standards. The difference is that krill oil starts cleaner by nature, while fish oil requires processing to get there.
Side Effects and Tolerability
The most common complaint about fish oil is the fishy aftertaste and reflux, sometimes called “fish burps.” Krill oil users report this less frequently, likely because the phospholipid structure digests differently and because the smaller capsule size means less oil per dose. If you’ve tried fish oil and couldn’t tolerate the gastrointestinal effects, krill oil is worth considering for this reason alone.
Both supplements can thin your blood slightly at higher doses, so the same cautions apply if you’re on blood-thinning medication. People with shellfish allergies should avoid krill oil, since krill are crustaceans.
Cost Per Milligram of Omega-3
Krill oil is significantly more expensive when you normalize for actual omega-3 content. A cost analysis found that fish oil supplements range from 1 to 15 cents per 100 milligrams of EPA and DHA, while krill oil runs about 30 cents for the same amount. That’s roughly 2 to 30 times more expensive, depending on which fish oil you’re comparing against. Combined with the lower omega-3 concentration per capsule, krill oil’s price gap widens further if you’re trying to reach higher daily doses.
Environmental Sustainability
Both industries face sustainability questions. Global fish stocks used for omega-3 production are under pressure from overfishing, and aquaculture creates its own ecological strain through the wild fish needed for feed. Krill harvesting is regulated by the Commission for the Conservation of Antarctic Marine Living Resources (CCAMLR), an international body that sets strict catch limits because krill are a foundational food source for whales, penguins, and other Antarctic species. Current catches remain well below those limits, but the ecological stakes of getting it wrong are high.
Which One Should You Choose
If your priority is getting the most omega-3 for the least money, fish oil wins. A concentrated fish oil supplement delivers more EPA and DHA per capsule at a fraction of the price, and the research base supporting its cardiovascular and anti-inflammatory benefits is deep.
If you’re willing to pay more for potentially better absorption, a built-in antioxidant, lower contamination risk, and fewer digestive side effects, krill oil is the stronger choice. It’s particularly appealing if you only want to take a low to moderate dose of omega-3s daily, where the absorption advantage matters more and the cost difference is manageable.
For most people, the honest answer is that both work. The best omega-3 supplement is the one you’ll actually take consistently, and for some people that comes down to whether they can stomach fish burps.