Fish oil and krill oil are food supplements that contain high levels of omega-3 fatty acids.
Omega-3s have several health benefits, including lowering inflammation and protecting your heart.
Fish oil comes from the tissue of fatty fish, while krill oil is made from Antarctic krill — crustaceans that look like tiny shrimp.
Fish oil and krill oil have different chemical structures, and the body may absorb them differently. One is also more expensive than the other and less widely available.
Some people, including those who are pregnant, may benefit from taking fish oil, krill oil, or other omega-3 supplements.
But these supplements can pose risks for some people. For example, people with high triglyceride levels who take omega-3 supplements may have a greater likelihood of developing atrial fibrillation, a heart rhythm disorder that can significantly increase your risk of stroke.
For most people, it’s best to get omega-3s by eating whole foods like fish and shellfish.
Not only do they contain lots of other healthy nutrients, but there’s also more evidence for some of the benefits of eating fish, compared with taking omega-3 supplements alone.
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What are the differences?
Fish oil comes from the tissue of fatty fish like salmon, mackerel, and anchovies, while krill oil comes from a species of small, shrimp-like crustaceans.
Here are some other differences between the two oils:
Color: Fish oil tends to be a golden yellow, while krill oil has a reddish shade.
Taste: Some people get a fishy aftertaste from fish oil capsules. People seem to report this less often after taking krill oil.
Composition: Fish oil contains more omega-3s than krill oil. But because of the way the body absorbs these fatty acids, this may not impact how much you actually take in.
Absorption: The different forms of omega-3s in fish oil and krill oil may affect how well your body absorbs them, though confirming this will require more research.
Cost: Fish oil supplements cost less to produce than krill oil supplements. They’re generally cheaper to buy.
The main benefits of both fish oil and krill oil supplements come from the omega-3s they contain.
Omega-3s are a group of polyunsaturated fatty acids, a type of fat that's usually liquid at room temperature.
Omega-3s are important components of cell membranes and influence how your cells communicate with each other.
They’re also involved in making hormones that regulate inflammation, blood clotting, and the functioning of your arteries.
Omega-3s are essential fatty acids. This means that your body can’t produce them on its own and has to get them from food.
There are three main omega-3s:
alpha-linolenic acid (ALA)
eicosapentaenoic acid (EPA)
docosahexaenoic acid (DHA)
ALA is in certain vegetable oils, nuts, and seeds. Your body can convert ALA into EPA and DHA, but only in small amounts.
Many people can get all the possible benefits of these supplements from dietary sources of omega-3s.
Cold-water fatty fish and other seafood are rich in EPA and DHA omega-3s, as are fish oil and krill oil.
Below, we look at some of the specific ways that these omega-3s may benefit our health.
May improve heart health
Triglycerides are a type of fat, or lipid, that circulates in your blood. Having high triglyceride levels increases your risk of heart disease.
There’s good evidence that consuming EPA and DHA can help reduce the triglycerides in your blood.
A 2017 review of 65 studies and articles showed that people who took a course of supplements containing EPA and DHA omega-3s saw significant reductions in their triglyceride levels both when fasting and after eating.
The results were similar for people who started out with high levels of triglycerides and those with normal levels.
Other researchers looking at the evidence in an earlier review found that people with high triglyceride levels tended to see a greater reduction after taking supplements.
They suggested that daily doses of 3–4 grams of EPA and DHA omega-3s were most effective. That’s about the amount in a 6-ounce serving of farmed salmon.
However, people with high triglyceride levels may have a greater likelihood of developing atrial fibrillation, a heart rhythm disorder, if they take omega-3 supplements. This condition greatly increases your risk of stroke.
So, omega-3 supplements may only help lower triglyceride levels if you take them before your levels get too high.
Omega-3s may also benefit heart health in other ways, such as by lowering blood pressure and improving blood vessel function.
Other possible health benefits
Here are some other areas of health where omega-3s may have benefits. But scientists need to do more research before they’re sure.
Rheumatoid arthritis: A number of small studies suggest that fish oil supplements may reduce symptoms. Plus, a larger nonclinical study found a link between eating more fish and having better results from rheumatoid arthritis treatment.
Dementia and cognitive health: One large, long-term study involving people aged 60–73 found that those who took fish oil supplements had a significantly lower risk of developing dementia.
Age-related macular degeneration: A review of studies found that people with more EPA and DHA omega-3s in their diets had 14–29% less risk of developing different forms of this eye health condition. The review didn’t look at whether supplementation might affect the risk, though.
Unless you have a vegetarian or vegan diet, the best way to get the omega-3s your body needs is to regularly eat fish and other seafood.
But some people might benefit from taking supplements as an extra source of omega-3s.
These groups include:
People who are pregnant or breastfeeding: EPA and DHA omega-3s are crucial to healthy development in the womb and after birth. The American Pregnancy Association recommends supplements to people who are concerned about eating fish during pregnancy. But it’s a good idea to speak with a healthcare provider before you start supplementing.
Older adults: As we’ve seen, taking omega-3 supplements later in life may help reduce the risk of dementia and other age-related diseases.
People who don’t eat seafood: If this is you, you may need to take supplements to get enough EPA and DHA omega-3s.
How to get omega-3s from your diet
It’s generally best to get your nutrients from whole foods if possible. When you eat foods that contain omega-3s, you get a whole host of vitamins, minerals, and other nutrients, too.
Animal sources of omega-3s
Cold-water fatty fish and other seafood are rich in EPA and DHA forms of omega-3. Some of the best sources are:
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Plant sources of omega-3s
Some seeds, nuts, and plant oils contain ALA omega-3s. And research suggests that these omega-3s may have their own health benefits.
Some plant sources include:
flaxseed oil and flaxseeds
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Which supplement is better, and should I try one?
For many people, eating enough fish is the best way to get omega-3s, along with the other nutrients fish contains.
Research has shown that eating fish improves heart health — while studies involving omega-3 supplements have been inconclusive.
But some people may benefit from taking fish oil or krill oil supplements.
If you’re choosing between these supplements, here are some things to consider:
Fish oil is cheaper and easier to find: Fish oil supplements are more likely to be at your local grocery store. Krill oil is also a lot more expensive than fish oil — up to ten times the price.
Absorption: Some scientists believe that our bodies absorb omega-3 molecules in krill oil more easily than those in fish oil. But a review of the research concludes that both oils still have the same effects on our blood fat levels.
Krill oil contains astaxanthin: Krill oil gets its reddish color from an antioxidant called astaxanthin. Antioxidants help protect your body from cell damage caused by molecules known as free radicals. One review suggests that astaxanthin may help slow the progression of heart disease. But confirming this requires more studies.
Overall, both oils are rich in omega-3s. And research hasn’t proven many of the supposed extra benefits of krill oil.
So, if you need to take a supplement, you may be better off going for fish oil.
Vegetarians and vegans
If you’re vegetarian or vegan, algal oil is an another way to get EPA and DHA omega-3s, which aren’t usually present at high levels in plant foods.
Manufacturers make these supplements from laboratory-grown microalgae.
While omega-3 supplements like fish oil and krill oil are generally safe, they can carry risks.
Some more minor side effects of taking omega-3 supplements include:
an unpleasant aftertaste or “fishy burps”
digestive issues, such as nausea or diarrhea
There are also reasons to take extra care if you’re thinking of starting omega-3 supplements.
Possible health risks include:
Drug interactions: Omega-3s can interact with blood-thinning medications, such as warfarin, and nonsteroidal anti-inflammatory drugs, such as ibuprofen. This might mean that it takes longer for a cut to stop bleeding, for example.
Seafood allergies: The National Center for Complementary and Integrative Health says it’s still unclear whether it’s safe for people with seafood allergies to take fish or krill oil supplements.
Atrial fibrillation: People with high levels of triglycerides in their blood may have a greater likelihood of developing atrial fibrillation, a heart rhythm disorder, if they take omega-3 supplements. This condition greatly increases your risk of stroke.
Make sure to discuss omega-3 supplements with a healthcare provider beforehand if you:
are currently taking blood-thinning drugs
have high triglyceride levels
are pregnant or breastfeeding
have allergies to fish or seafood
are thinking of giving them to a child
Fish oil and krill oil are both dietary supplements that have high levels of the omega-3 essential fatty acids EPA and DHA.
Unless you’re vegan or vegetarian, you can probably get all the omega-3s that you need, along with other beneficial nutrients, from food rather than supplements.
If you’re vegetarian or vegan, you can get EPA and DHA omega-3s from algal oil.
Other people, including those who are pregnant, may benefit from taking a fish oil, krill oil, or algal oil supplement. It’s a good idea to talk to a doctor first, especially if you take certain medications — or if you have high triglyceride levels, atrial fibrillation, or a seafood allergy.
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