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Nutrition Corner: Fish Oil

Fish oil is one of the most widely studied supplements in the medical field. It has been touted as THE supplement for a wide variety of conditions from skin allergies to kidney and heart health. But what exactly is in fish oil? Why does it work? And how can you be sure your pet is getting a high quality and effective product?

What is Fish Oil?

Fish oil is the primary source for two different Omega-3 fatty acids - eicosapentaenic acid (EPA) and docosahexaenoic acid (DHA). These two compounds serve as precursors to eicosanoids that have been definitively proven to decrease inflammation in the body.

As the name implies, fish oil is derived from the tissues of oily cold water fish such as salmon, herring, mackerel, anchovies, and sardines. However, these oily fish do not endogenously produce EPA and DHA - they need help from their diet. By

consuming microalgae and plankton, these fish are able to absorb and convert these nutrients to the fish oil we later purchase from the store.

Fatty acids can also be found in many plants such as chia seeds, flaxseed, brussel sprouts, algal oil, hemp seeds, walnuts, and perilla oil. It should be noted though that dogs and cats cannot effectively convert plant sources of fatty acids into DHA and EPA.

Obtaining fatty acids from fish oil does not come without problems. Fish oil products can succumb to contamination, inaccurate listings of EPA/DHA levels, spoilage, and formulation issues. Multiple third party testings of commercially available fish oils have found mercury, dioxins, polychlorinated biphenyls (PCBs), radioactive substances such as strontium, cadmium, lead, chromium, and arsenic - many of which can be carcinogenic if ingested over time. Many fish oil products contain very little actual EPA/DHA in them, sometimes only composing 8% of the total fish oil content. Cod liver oil is a popular fish oil supplement, however in reality it has very little EPA/DHA and instead has large amounts of the active form of Vitamin A, which if ingested in excess can cause Vitamin A toxicity.

With all the potential pitfalls of fish oil supplementation, what is a pet owner to do? Consider reaching for krill oil instead; this is a very effective substitute and usually of a much higher quality than many fish oil products. It is much more resistant to oxidation (discussed below) and since krill are so small they cannot accumulate hard metals nearly to the degree that fish can.

Known Benefits

The more fatty acids are researched, the more we realize how important of a body building block they truly are. Fatty acids have been shown to provide a beneficial effect to canine patients suffering from the following conditions:

  • Heart problems, such as Congestive Heart Failure, Dilated Cardiomyopathy, and Atrial Fibrillation

  • Inflammatory skin disorders, including idiopathic itching, flea allergy dermatitis, and confirmed environmental allergies

  • Renal disease

  • Osteoarthritis and joint disease

  • Hyperlipidemia, often the cause of lipoma formation and pancreatitis in dogs

In addition, new exciting research is coming out showing possible benefit of fatty acid supplementation in the treatment of certain yeast infections, Inflammatory Bowel Disease, certain cancers, cognitive function, neurologic health, and aggression.

Safety Concerns

It is thought that 25-50% of all fish oil products on the market are damaged and may do more harm than good! Fatty acids from fish oil are highly volatile and will oxidize within one hour if exposed to oxygen and/or UV light. Oxidation causes the EPA and DHA to be converted from an antioxidative species to an oxidative species. Oxidation can at best make the EPA and DHA ineffective, and at the worst cause cell death and damage to proteins, lipids, and DNA in the body. Krill oil is a much better and safer source of Omega-3. Much of this is due to its size, but also because most krill comes juxtaposed with astaxanthin, a natural protectant against oxidation. While fish oil can go rancid from oxidation within one hour, krill oil resists oxidation for up to 190 hours.


  • Don’t wait: Fatty acid supplementation works best when given as a preventative or in the early stages of many disease processes

  • If buying fatty acids from a fish oil source, consider purchasing in either gel caps or an airless pump form to avoid a greater risk of oxidation over time. Also buy in small batches and keep refrigerated.

  • My best recommendation is to utilize krill oil for fatty acid supplementation in pets. Make sure the krill oil you purchase also contains astaxanthin to help further prevent spoilage.

  • Remember that cod liver oil is a great source of Vitamins A and D, but not an abundant source of Omega-3




  3. Cameron-Smith, David, Benjamin B. Albert, and Wayne S. Cutfield. “Fishing for Answers: Is Oxidation of Fish Oil Supplements a Problem?” Journal of Nutritional Science 4 (2015): e36. PMC. Web. 29 Dec. 2017.



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