Flaxseed Oil vs. Fish Oil

You can find statements like the following in a hundred places:

Both fish and flax are good sources of omega-3. Flaxseed oil is less expensive, which can be an important consideration. The main difference is that flaxseed oil contains only alpha-linoleic acid (ALA), which is the parent compound from which other omega-3 fatty acids are derived. This leaves it to your body to do the conversion to the other forms it needs, eicosapentaonoic acid (EPA) and docosahexaenoic acid (DHA). The problem is that the conversion is not always that efficient, and the body often uses the ALA for extra energy, leaving less for conversion to the other types. The body uses various enzymes to convert ALA to other omega-3s, and the process is not very efficient, especially as one gets older. Estimates of the rate of conversion range from 5% to 25%. In order to make sufficient amounts of EPA and DHA, one needs to consume 5-6 times more ALA than if one relies on fish oil alone. Fish oil, on the other hand, contains the other forms and delivers them directly to your body with no conversion necessary.

It isn’t that simple. Here are three things I rarely see mentioned:

1. The conversion rate is not fixed. It depends on the amount of the conversion enzyme, which increases with ALA exposure. The body makes the enzymes it needs and doesn’t make the enzymes it doesn’t need. You don’t have enzymes to digest food you don’t eat — but if you start to eat them you will build up the enzymes. The measurements of ALA conversion rate I have seen measured the conversion rate without giving the subjects extensive exposure to ALA before the test. (Measurements of glycemic index have the same problem.) They should be considered lower bounds of what would happen with long exposure.

2.  Time release is good not bad. When you take a dose of flax oil, its ALA is converted to DHA and EPA, which takes time, thus smoothing out the supply versus time function. If you take a dose of fish oil, the brain receives a sudden burst of DHA and EPA. It is likely that a smoother supply is better.

3. ALA (omega-3) conversion blocks AA (omega-6) conversion. Omega-3 fatty acids and omega-6 fatty acids are almost identical. The enzyme that converts short-chain omega-3 to long-chain omega-3 also converts short-chain omega-6 to long-chain omega-6. Long-chain omega-6 probably has bad effects in your brain, at least in large amounts, because it displaces long-chain omega-3. For industrial reasons, our diets are high in short-chain omega-6. Having ALA in your system, which flax oil provides but fish oil does not, slows down the conversion of short-chain omega-6 to long-chain omega-6 by occupying the conversion enzymes.

Thanks to Gary Skaleski.

9 Replies to “Flaxseed Oil vs. Fish Oil”

  1. No reason to debate this. Take a omega 6/omega 3 ratio blood test and you will know what works for you.

    I take such a test every six months. My last test was 2.85 to 1. 2 to 1 is ideal so I am close enough. i take fish oil and I eat omega 3 eggs. Omega 3 eggs are made by feeding chickens flax seed. A chicken body is better at converting ALA than mine is.

    Your experience may differ.

  2. Two tablespoons of flaxseed oil a day has completely eliminated my dandruff. Two tablespoons of cod liver oil did not (nor did two tablespoons of olive oil or of butter). I have no idea why this might be the case, but for me, at least, flaxseed oil provides something the others do not.

  3. Interesting. Conventional wisdom out here in fix-autism-with-nutrition-land is to go with fish oil and evaluate based on DHA count and processing method. (Yay Kirkman!)

    The story behind it is roughly the same except that kids with Autism are bad a converting ALA to DHA/EPA.

    I’d like to know where the notion came from that you “build up” enzymes by requiring them over time. I hadn’t that before. Is it common knowledge?

  4. @Darrin
    Enzymes are proteins…(DNA makes RNA makes protein). Some enzymes are constitutive (made all the time in fairly stable amounts because they are needed for routine, house-keeping functions), while others are inducible (the amount that is made depends on how much is needed for special functions).

    If all the proteins a cell could make were made all the time, the cell would run out of space and/or not be very efficient.

    This is pretty easy to demonstrate in bacteria. They prefer to use glucose, but when there is no glucose left in their medium, but there’s some lactose, they will turn on the genes that make the enzyme that breaks down lactose. If you add glucose back to their diet, they turn off the lactose-digesting genes and return to glucose fermentation.

    We do this too. If you feed a diet high in protein, there is an increase in enzymes that degrade amino acids in the liver, as long as the influx of amino acids continues.

  5. Considering that the enzyme for ALA conversion would be upregulated with continuous intake, it could explain why your optimal dose went from 4 T to 2 T, Seth, don’t you think?

  6. Professor Roberts:

    After reading your blog for some time, last year I started flaxseed oil (2TBSP). After one year, my total blood cholesterol went down (206 to 194), HDL increased and triglycerides decreased (110 to 55). Exercise and diet remained constant year over year, except that 6 months ago I began large amounts of butter and one Greek yogurt a day.


  7. HI

    My name is Gonçalo and I’m from Portugal.

    I really like your blog so that’s why I thought about asking you a question.

    I have struggled with strong chronic anxiety and some depression for a long time. I’m 23.

    I would like to ask you if you have any suggestion about what I can do to to try to understand if these syntoms have roots in nutritional deficiencies, infections, inflammation, etc. I have
    some history of trauma but maybe some of this is aggravating the problem?

    Are there some probable causes? Any tests I shoud do? cost-effective Solutions?

    Thanks so much

    Warmest wishes


  8. Gonçalo, I believe that a common cause of depression and anxiety is a messed-up mood rhythm This rhythm is generated by an internal oscillator with a 24-hour cycle that controls our mood.

    To work properly this oscillator needs:

    1. exposure to sunlight in the early morning
    2. no fluorescent light late at night.
    3. exposure to faces in the early morning,
    4. no exposure to faces late at night.

    If any of the four is missing it doesn’t work. And when it doesn’t work you are at greater risk of depression.

    You can read more about this in Example 2 of my long self-experimentation paper:


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