Fish Oil vs Krill Oil: Which Omega-3 Supplement Is Better?

Fish oil and krill oil both supply the omega-3 fats EPA and DHA, which support heart, brain and eye health. Krill oil often costs more and is marketed as a premium upgrade. Is it? Here's how fish oil vs krill oil compares on dose, absorption, evidence and price.

Quick comparison

The dose gap is the deciding factor

The single most important number on an omega-3 label is combined EPA + DHA per serving, not the "fish oil" or "krill oil" total.

A typical 1,000 mg fish oil softgel contains around 300 mg of EPA + DHA, and concentrated versions reach 600–900 mg. A typical 500 mg krill oil softgel contains roughly 100–150 mg.

To get 500 mg of EPA + DHA a day, you might need one or two fish oil capsules, or three to five krill oil capsules. At typical retail prices, that makes krill oil several times more expensive for the same omega-3.

Does krill oil absorb better?

Krill oil's omega-3s are bound mainly to phospholipids, the same kind of fat that makes up cell membranes. Supporters argue this improves absorption.

The evidence is mixed. Some studies found krill oil raised blood omega-3 levels about as much as a larger fish oil dose. Others found no meaningful difference when doses were matched. Reviews conclude that any absorption advantage is modest and not enough to offset the lower dose per capsule.

What does the research support?

Most of what we know about omega-3 supplements comes from studies of fish oil or prescription EPA/DHA:

• Triglycerides: High doses (2–4 g per day of EPA + DHA, by prescription) can lower high triglycerides.
• Heart health: Large trials of standard-dose fish oil in the general population have shown mixed results. Benefits seem stronger in people who eat little fish.
• Eyes, brain, mood and joints: Evidence ranges from promising to inconclusive, again mostly with fish oil.

Krill oil studies are fewer, smaller and shorter. That doesn't mean krill oil doesn't work, only that fish oil has much more evidence behind it.

Safety and side effects

Both are generally safe at normal doses. Common side effects include fishy aftertaste, burping, heartburn and loose stools. Taking omega-3s with a meal reduces these, and it also helps absorption, just as it does for vitamin D and other fat-soluble nutrients.

Keep in mind:

• Blood thinners: Omega-3s at higher doses may slightly increase bleeding risk with warfarin or similar drugs. Ask your doctor.
• Atrial fibrillation: Some trials found a small increase in AFib risk with high-dose omega-3 supplements in people with heart risk factors.
• Seafood allergies: Krill is a crustacean. If you have a shellfish allergy, ask your doctor before taking krill oil.
• Upper amount: The FDA considers up to 5 grams per day of EPA + DHA from supplements safe.

Sustainability and purity

Both fish and krill can be harvested sustainably. Look for MSC certification (Marine Stewardship Council) or Friend of the Sea. For purity, choose products tested for mercury, PCBs and oxidation by IFOS, USP or NSF. Fresh oil shouldn't smell strongly rancid.

Which should you choose?

Choose fish oil if:

• You want the most EPA + DHA for your money
• You want the form with the strongest research
• You're aiming for higher doses

Choose krill oil if:

• Large capsules are a real barrier for you
• You only need a modest dose and value small softgels over cost

The verdict

For most people, concentrated fish oil is the better buy. It delivers more omega-3 per capsule and per dollar and is backed by far more research. Krill oil is a reasonable alternative if you prefer small capsules, as long as you check that the EPA + DHA amount is enough. And if you eat fatty fish twice a week, you may not need a supplement at all.