Answer:

Fish oil and flaxseed oil each provide omega-3 fatty acids, but only fish oil contains the omega-3s EPA and DHA, and has been shown to be helpful for conditions such as rheumatoid arthritis, inflammatory bowel disease, and depression. High-dose fish oil may help to lower very high triglyceride levels.  

Flaxseed oil, on the other hand, contains the omega-3 fatty acid ALA (alpha-linolenic acid) -- a very small percentage of which is converted into EPA and, to a lesser extent, DHA in the body. For this reason, it may be useful as a dietary supplement for people who are not getting EPA or DHA from fish/marine oils, however, because such small amounts are converted, it will not provide the clinical benefits shown for oils containing EPA and DHA. Studies show flaxseed oil may help to improve dry eye symptoms in people with the autoimmune disease Sjogren's syndrome, and may help to lower "bad" cholesterol in some people, but there is little evidence it's helpful for any other specific conditions.  

Neither fish oil from supplements nor flaxseed oil appear to reduce the risk of cardiovascular disease or stroke, unless a person has recently had a heart attack. In contrast, eating fish regularly does lower the risk of cardiovascular disease and eating ground flaxseeds (not just the oil) may help lower high blood pressure. 

Be aware that fish oil and flaxseed oil may have each have potential blood-thinning effects, which might be increased if you are taking both.  

For more about the uses, clinical evidence, and side effects for these supplements, plus ConsumerLab.com's tests of products, see the Reviews of Fish Oil and Omega-3 Fatty Acid Supplements and Flaxseed Oil, Evening Primrose Oil, Borage Oil, and Black Currant Oil Supplements.

Also see the Encyclopedia articles about Fish Oil and Flaxseed Oil.

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4 Comments

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Jeanette 5805
June 15, 2015

Can you please tell me how to buy a gift subscription?
Thanks.

ConsumerLab.com
June 16, 2015

Hi Jeanette - You can order a gift membership here: https://www.consumerlab.com/GiftCerts/

Jeanette 5804
June 15, 2015

You have not mentioned Omega 3 from algae. I take a supplement called Ovega and have for years and it has benefited me with depression and has raised my HDL.

ConsumerLab.com
June 16, 2015

Hi Jeanette - Thanks for letting us know about your experience with algal oil, which can also be a good source of EPA and DHA, as discussed in the Fish Oil and Omega-3 Fatty Acids Supplements Review: https://www.consumerlab.com/reviews//omega3/#algal.

You can find our tests of algal oil supplements, including an Ovega product, plus tests of fish, krill calamari and green-lipped mussel oil supplements here: https://www.consumerlab.com/reviews//omega3/#results.

Joseph20824
August 28, 2020

Can I just say how refreshing it is to see responses to questions from the originator of the content? You guys at Consumer Lab are truly awesome.

ConsumerLab.com
August 31, 2020

Thank you for your kind words.

Jane18016
June 11, 2019

How about iodine content of fish oil capsules? I have Hashimoto's and iodine can be a problem in too high a dose, but I have to bring my Omega 3's up.

ConsumerLab.com
June 11, 2019

Hi Jane - Concentrated fish oil supplements are not known to be significant sources of iodine, unlike fish meat.

David1718
May 18, 2015

I have been taking ground flax for over 12 years. It does not lower cholesterol. What it does do is increase the good HDL between 12 and 17%. For years I always had a problem with getting a high enough reading of good cholesterol and now I am fine. But as some of my friends learned when they tried it, do not take more than one tablespoon as too much may cause facial flushing much like niacin or a case of diarrhea. I read a study put out by the Canadian Flax Seed Counsel but I also was told about it by three friends who had experienced the same increase in good HDL but warned it did nothing to lower directly LDL by itself but only increased HDL and subsequently did lower LDL.

ConsumerLab.com
May 19, 2015

Hi David - Thanks for letting us know about your experience with ground flaxseed. Facial flushing has been reported by some people, although this does not appear to be reported in the medical literature. Rare cases of allergic reactions to flaxseed have been reported, however. You can see the Cautions and Concerns section of the Flaxseed Oil Review for more about this: https://www.consumerlab.com/reviews//flaxseed/#cautions

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