New Facts about Flax

The omega-3 family of fatty acids receives quite a bit of attention these days, and with good reason. We have known for some time that increasing omega-3 fatty acids and improving the ratio of omega-6 to omega-3 fats in our dogs’ diets is associated with certain health benefits. Although the effects of adding these fats to a dogs’ food are often overstated, it is probable that increasing omega-3 fatty acids in dogs’ food is a healthful dietary change to make.

The Three Omega-3s

First, just a bit of background. Remember that fatty acids can be classified into families. The two that are most important nutritionally are the omega-6 fatty acids and the omega-3 fatty acids. Both types are important in the diet, but our present day dog foods (like human foods) tend to contain an over-abundance of omega-6 fatty acids simply because of the types of ingredients that are produced by our modern-day agricultural system. Linoleic acid and arachidonic acid are both omega-6 fatty acids, with linoleic acid being the parent omega-6 fatty acid from which all others are derived.

The three fatty acids in the omega-3 family that are important nutritionally are the parent fatty acid alpha-linolenic acid (ALA), and its long-chain derivatives, eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). It is these two latter fatty acids, EPA and DHA, that are associated with various health benefits. EPA is helpful for reducing inflammatory responses in the body and DHA is needed, especially in puppies, for optimal neurological and visual development. (For complete reviews of these fatty acids and their benefits, take a look at The Science Dog Course, “Basics of Canine Nutrition“)

Conversely, ALA, while possibly having some independent benefits of its own, (these are not well documented in dogs to date), is most frequently discussed in the context of being the precursor fatty acid of EPA and DHA. The supposition is that if a food is enriched with ALA (from various plant sources, one of which is flax), that we then are also enriching the dog’s diet with EPA and DHA because EPA and DHA are subsequently produced in the body from the dietary source of ALA.

But, Here is the Rub

Although most mammals, including dogs, can convert some ALA to EPA and DHA, they do not do this very well. For dogs, we know that neonates (newborn pups) are most efficient and that this ability gradually declines as puppies reach adulthood. The ability of adult dogs to convert ALA to EPA and DHA may be too low to effectively increase the long-chain and beneficial omega-3 fatty acids in the body’s blood and tissues. For this reason, the source of the omega-3 fatty acids in a dogs’ diet becomes an important consideration.

Why Fish?

Interestingly, marine algae are the most efficient and the most prolific converters of ALA to EPA and DHA. Subsequently, certain species of cold-water fish (those that eat either algae directly or those that consume marine creatures that eat the algae… know… chains and all….), become concentrated sources of EPA and DHA. For dogs, fish oils such as salmon, menhaden and herring oil all are direct sources of the long-chain omega-3 fatty acids (i.e. they bypass need for the body to convert ALA to EPA and DHA)

What about Flax?

If this is true, why then why is flax and flaxseed oil so frequently promoted as a beneficial source of omega-3 fatty acids in commercial dog foods or for use as a dietary supplement? Flax is a concentrated source of ALA (but contains no EPA or DHA at all). It is included in commercial pet foods because it is a relatively inexpensive and sustainable way to increase a food’s concentration of total omega-3 fatty acids (see “Does this Seem (Not) Fishy to You” for more about this). The presumption has been that, as a source of ALA, flax effectively leads to increased EPA and DHA in a dog’s blood and tissues. However, this supposition is a bit fishy (don’t you agree) since we know that dogs are not very efficient converters of ALA to EPA and DHA.

Recently a group of researchers at Norway’s Aker BioMarine Antarctic AS (a producer of krill oil) decided to confront this issue head-on by testing the ability of flaxseed oil to influence the EPA and DHA status of adult dogs. Here is what they did:

The Study

The researchers’ objectives were to study the effects of feeding either a source of ALA (flaxseed oil) or a source EPA and DHA (krill oil) on an accepted measure of omega-3 fatty acid status (called the Omega-3 Index) in adult dogs. The Omega-3 Index involves measuring the levels of EPA and DHA in circulating red blood cells.

Twenty adult Alaskan Huskies were included in the study. All of the dogs were fed the same complete and balanced dog food; 10 were supplemented daily with flaxseed oil to supply 1.068 mg of ALA and 10 were supplemented with krill oil to supply 1.15 mg of EPA/DHA. The study was 6 weeks in length. Blood fatty acid levels and Omega-3 Index were measured at the start of the study (Week 0), midway through (Week 3) and at the end of the study (Week 6).

  • Krill Oil: The long-chain omega-3 fatty acids, EPA and DHA increased significantly in the dogs who were fed supplemental krill oil, but not in the dogs fed supplemental flaxseed oil. This difference was quite dramatic – the Omega-3 Index increased by more than 60 percent (1.68 % to 2.7 %) in the dogs fed krill oil.
  • Flaxseed Oil: Conversely, the index in dogs fed flaxseed oil actually decreased significantly during the study period, going from 1.6 % to 0.96 %.
  • Flax Feeding: These results provide strong evidence that including flax in the diets of dogs with the intent of improving their omega-3 fatty acid status is not effective and that providing a direct source of the long-chain omega-3 fatty acids (EPA and DHA) from a fish oil (such as krill oil) is highly effective.
The graphic below, taken from the study, illustrates this dramatic difference between the two groups.
From: Dominguez et al; Enhanced omega-3 index after long- versus short-chain
omega-3 fatty acid supplementation in dogs, Vet Med Sci 2020; 00:1-8

Take Away for Dog Folks

These results provide impressive evidence that feeding flax to dogs may not be an effective means of enhancing omega-3 fatty acid status, when the goal is to increased EPA and DHA levels in tissues. (Note: The index that was used, a measure of fatty acids that are incorporated into circulating red blood cells, was used because it is an accepted indicator of whole-body (tissue) omega-3 status).

Another benefit of krill meal and oil, which is a relative newcomer on the pet food ingredient market, is that krill, specifically Antarctic Krill (Euphausia superba), is considered to be a sustainable source of marine long-chain omega-3 fatty acids. This is also true of several specific types of micro-algae, another relative newcomer to the omega-3 pet food/supplement marketplace.

So, Science Dog readers – When you look at omega-3 fatty acids on dog food labels, make sure that you examine the sources of these important fatty acids!

Look for fish (or algae), not flax.

Feel welcome to comment, letting us know what you feed (or supplement) to your dog, and why!

Happy Feeding!
Fish Oil or Flax? Which is Better for Dogs?

Cited Study: Enhanced omega-3 index after long- versus short-chain omega-3 fatty acid supplementation in dogs. Veterinary Medicine and Science 2020: 00; 1-8.DOI: 10.1002/vms3.369

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10 thoughts on “New Facts about Flax

  1. Pingback: Krill – The Other Fish Oil – The Science Dog

  2. I’m very concerned about commercial krill harvest increasing to the point of imperiling ocean populations (like baleen whales) that depend on krill. Doesn’t seem sustainable to me in the bigger picture.

    Liked by 1 person

    • Hi Janis, This is a very good point. When I tried to find out more about how truly sustainable krill are, it seems that there is not agreement. While some sources maintain that it is a renewable source of fish oil, others (like you) question this and are concerned about its recent increase in use. After reading a bit more (and noticing that many of the sustainable claims are coming from the fish oil industry), I am leaning towards your view. I will try to find out more – thanks for bringing this up. Linda


  3. Reading this I was reminded I had made an inquiry of a premium freeze dried dog food back in January and one of the questions I had was in regard to the omega 3’s listed. At that time Omega-3 as listed as 5% min. I noted flaxseed was listed in the ingredients but no other sources were listed. One of my questions was “Does the food contain EPA and DHA? If so, what is the source?”
    The answer I received was surprising.
    “Our food does contgain EPA & DHA. Unfortunately, we do not know where it derives from” …” I will need to contact our product developers for more information. Once we have the requested information, I will contact you via e-mail as soon as the information is available.”

    I just checked the website and see that omega 3 is now listed at 2.5% min and that salmon is now listed in the ingredients.

    I never did receive any further information from the company.

    Liked by 1 person

    • Hi Glenn – Oh dear. How could they possibly not know the source of their listed levels of EPA and DHA (and why would the company allow a support staff to answer in such a way??). And then not to hear anything more……sigh…..hate hearing experiences like this. It is interesting that salmon is now included in the ingredient list. Thanks for posting, even if it is about a frustrating experience! Linda


  4. This study seems to specifically measure EPA/DHA blood levels as an outcome – are there not other benefits (beyond the synthesis of EPA/DHA) to higher intake of ALA? I don’t believe it has been studied in dogs, but the anti-inflammatory properties of ALA have been compared with comparable amounts of EPA/DHA from fish oil and the ALA resulted in more anti-inflammatory biomarkers (at least in rats with colitis and human cardiovascular inflammation). One of the studies here:

    While it appears algae- or fish-derived oil is critical for many of the benefits associated with omega-3s, it does not seem like this study would suggest that flax and other sources of ALA should be entirely discounted. From what you’ve seen, do you believe that higher ratios ALA and other PUFAs are still preferable as a % of total fatty acid content (i.e. versus additional MUFAs or saturated fats)?


    • Hi Garrett, Thanks for posting; these are great points. Currently, ALA is considered to be, at the very least, a conditionally essential fatty acid for dogs (and many now classify it as essential and have dropped the ‘conditional” qualifier). At issue is exactly what you mention – there is not a lot of strong evidence that ALA alone has demonstrated health benefits – at least not the anti-inflammatory benefits of EPA or the neurological/visual benefits of DHA. Rather, is certainly (and I would argue probably) is the primary source of EPA and DHA when dietary omega-6 fatty acids are not so predominant (which has occurred because of the types of crops that we grow and feed to animals).

      As you note, we cannot forget that ALA the parent omega-3 fatty acid and that it competes for the same set of enzymes as the omega-6 fatty acids need for elongation and desaturation. There is no doubt that it is needed, and possibly if the omega-6 fatty acids (total) are reduced in a food, that because of the reduction in competition, we might see more conversion than what has been typically reported. The base food that was used in this study did have ALA (~500 mg/100g), but had an omega-6 to omega-3 fatty acid ratio of ~8.5:1. This is not crazy high in omega-6s, but I do wonder if it had been a bit lower, might we have seen more conversion (this is just speculation, of course).

      One thing to keep in mind is that we need to differentiate between what may be an essential nutrient (probably ALA) and what we see as nutrition-related health benefits (as demonstrated with [still unknown levels, really] with the anti-inflammatory benefits of EPA. As far as DHA goes, we know that neonatal puppies can get the elongated fatty acids, especially DHA, from their mother’s milk and that they are most efficient converters of ALA to DHA at this age – which suggests that they are capable of producing/obtaining adequate DHA at the time of life that they need it most.

      So, to answer your last question, I think the point of this study (and my essay about it) is not to say that ALA is not needed (it almost certainly is) or that the ratio of omega-6 to omega-3 fatty acids should be lower than it is in many foods (again, no argument there), but rather, if an owner selects a pet food that promotes itself as being high in omega-3 fatty acids but its source is ALA alone, AND the food’s label suggests that a dog will accrue benefits associated with EPA or DHA from the food, then such a supposition should be questioned, as simply including flax, while increasing ALA, will not increase tissue levels of EPA or DHA (at least when a food that has a ratio of ~ 8.5:1 is fed).

      Thanks again – love getting questions like yours! Happy Holidays! Linda


      • Thank you for the detailed response and clarification. I wasn’t aware that EPA was the suspected driver of most anti-inflammatory responses. The 6:3 ratio and competition for enzymes is an interesting variable (but introduces a ton of permutations).

        The marine algae oils seem to be good sustainable options and we’ve found they are becoming more affordable. Thanks again for sharing your perspective.


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