Rather than cover every aspect of lipids, or fats, we’re going to focus specifically on the omega-3 and omega-6 families of polyunsaturated fatty acids, also called PUFAs, and their role in nutrition. To properly explain fatty acids, understanding their structure can be beneficial. There are many different types of fatty acids, and they are made up of chains of carbon atoms with a carboxyl group at one end, and a methyl group at the other end. The length of these carbon chains determines whether a fatty acid is a short-chain (less than 8 carbon atoms), medium-chain (8-12 carbons), or long-chain (more than 12 carbons). The amount of carbons will ultimately determine the fatty acid’s digestion, absorption, and usage within the body.
Those carbon atoms are saturated with, or bonded to, hydrogen atoms. If a fatty acid is saturated with hydrogen- that is, no two carbon atoms are bonded to each other- it is a saturated fatty acid. If there is one spot in its carbon chain where two carbon atoms are bonded (double bond), then it is a monounsaturated fatty acid. If there is two or more spots in its carbon chain where two carbon atoms are bonded, then it is a polyunsaturated fatty acid. It’s important to note that the more double bonds in the carbon chain, the more susceptible the fatty acid is to oxidation. We’re going to cover that a little further down.
Focusing on the unsaturated fatty acids, we can break those down further into three different omega families: omega-9, omega-6, and omega-3. This classification is determined by how far down the carbon chain the first double bond appears (from the methyl group). If it appears 9 carbons down, then it is an omega-9. If it appears 6 carbons down, then it is an omega-6. If it is 3 carbons down, then it is an omega-3. Omega fatty acids can either be essential, meaning they must be provided in the diet, or non-essential, meaning the dog can synthesize them on its down. Essential fatty acids will be abbreviated as EFAs for the remainder of this guide. Because omega-9 fatty acids are non-essential, we will not be covering them here!
Omega-6 fatty acids are essential within the diet. The parental form, meaning the form needed to synthesize other omega-6 fatty acids, is called linoleic acid. Lineolic acid (LA) can then be synthesized within the dog’s body to arachidonic acid (AA), which is the most physiologically important omega-6 fatty acid.
Omega-3 fatty acids are essential within the diet. The parental form, meaning the form needed to synthesize other omega-3 fatty acids, is called alpha-linolenic acid (ALA). The most physiologically important omega-3 fatty acids are eicosapentaenoic acid (EPA), and docosahexaenoic acid (DHA).
The body cannot convert omega-6 fatty acids to omega-3 fatty acids or visa versa.
OMEGA-6 FATTY ACIDS: FUNCTIONS & DEFICIENCY SYMPTOMS
Linoleic acid is the parental form of arachidonic acid for dogs. Providing enough linoleic acid means that arachidonic acid doesn’t have to be provided in the diet; however, it would be rare for a raw fed dog to not receive any arachidonic acid dietarily, as it’s found in appreciable amounts in animal fat. Arachidonic acid is synthesized in the liver and possibly in limited amounts in the skin.
Omega-6 fatty acids have distinctly different functions within the body. They are essential for:
- maintaining the water barrier of the skin
- maintaining cell membrane fluidity, structure, permeability, and function
- protein interaction for cell signaling,
- energy metabolism, and
- gene expression
In addition, AA is a precursor for a group of compounds called eicosanoids. Eicosanoids are immunoregulatory molecules that have localized hormonelike effects and are associated most commonly with inflammatory responses,
Despite the negative connotation of being “pro-inflammatory”, it’s important to remember that 1.) the inflammatory response is required for proper response to trauma within the body so we should not be attempting to remove the inflammatory response entirely, and 2.) omega-6 fatty acids are required for skin and coat health. That second point means that during times of reduced skin and coat quality, we shouldn’t just be looking at omega-3 fatty acids!
Because skin and coat health are determined by the presence of linoleic acid, a deficiency can manifest as
- dry, scaly skin or extremely greasy skin,
- skin lesions,
- slow wound healing, and
- and increased susceptibility to bacterial infections
OMEGA-3 FATTY ACIDS: FUNCTIONS & DEFICIENCY SYMPTOMS
Alpha-linolenic acid (ALA) is considered the parental form of EPA and DHA because dogs can technically utilize it to metabolize EPA and DHA, but studies have shown that the rate of conversion to EPA is low (<10%) and the conversion to DHA appears to be nonexistent. For those reasons, it is best to provide dietary sources of EPA and DHA; in fact, if one wants to utilize EPA to modify the body’s inflammatory response, dietary EPA must be provided (meaning that a dog cannot synthesize enough EPA from ALA to modify his own inflammatory response).
ALA’s primary role is to be available to produce EPA, but it also secondarily has a sparing effect on the omega-6 linoleic acid which does allow it to be beneficial for skin and coat health.
ALA appears to have a nonexistent conversion rate to DHA. There are several possible explanations:
- ALA has other metabolic fates beyond conversion to long chain omega-3 fatty acids that remain in a balance
- There is competition between omega-6 and omega-6 fatty acid synthesis enzymes in the liver, which will directly affect the amount of DHA accumulated by ALA
Like AA, EPA is a precursor for eicosanoids, but the types produced by EPA are considered to be anti-inflammatory in nature because they are significantly less potent than those produced by AA.
For this reason, EPA can be used to modify or blunt the inflammatory response of the body, making it useful for a myriad of health conditions where anti-inflammatory processes are needed. EPA is well-known for its use in treating inflammatory skin conditions; it produces a product called resolvin that reduces inflammation and limits leukocytes, a type of white blood cell, from infiltrating inflamed tissues.
Docosapentaenoic acid, or DPA, is an intermediate fatty acid that is needed for DHA synthesis. DPA can be produced by the body in the liver from ALA -> EPA, and it is then transported to tissues in the body (neurological and retinal tissues, specifically) where it acts as a substrate for the final conversion to DHA.
DPA can be supplied dietarily as well, with the highest concentrations found in seal oil.
DHA has its own, very specific set of functions that are different from any other EFA. It is concentrated in the cell membranes of neurological tissues (central nervous system and brain) and in the retina and it is required for proper neurological and visual development and maintenance, beginning in utero and continuing into geriatrics. Gestating and lactating bitches should be supplemented with DHA so that fetuses and newborn puppies receive adequate levels, first through the placenta and then through milk, where DHA will be concentrated. Puppies supplemented with fish oil show faster response times, improved trainability and memory, and better response in dim light. In senior dogs, supplementation with DHA may improve or slow the progression of the symptoms of canine cognitive disorder.
A true deficiency is not common in dogs (meaning that the dog’s minimum requirement is not met), but
- chronic inflammatory conditions,
- impaired vision,
- nervous system abnormalities, and
- reduced capability for learning and memory retention
could be symptoms of an EPA and/or DHA deficiency, especially during puppyhood.
Eicosanoids produced by precursor fatty acids include four types of compounds: the prostaglandins, prostacyclins, thromboxanes, and leukotrienes. Eicoanoids are immunoregulatory molecules that have localized hormonelike effects and are involved with inflammatory responses, immunoregulation, and skin cell proliferation; they may have a vasodilation or vasoconstriction effect; or they may be protective of cell types (such as those produced in the gastrointestinal tract). They are synthesized on demand in response to their immediate environment. If a cell is damaged, its membrane releases a fatty acid and metabolizes it into an eicosanoid. If the type of fatty acid metabolized is an omega-6 (AA), then the resultant eicosanoids are generally considered to be pro-inflammatory, although this is an oversimplification as some of the eicosanoids produced by omega-6 fatty acids can also inhibit other pro-inflammatory compounds. An example here is gamma-linoleic acid or GLA, sourced from borage oil, which is more similar to EPA in regards to the eicosanoids it produces.
The inflammation response will increase the blood supply to the inflammation site, which in turn leads to increased capillary permeability, allowing leukocytes to migrate into the tissue from the capillaries. Once there, the leukocytes will release mediators like the prostaglandins or the amino acid derivative histamine; these mediators can worsen the inflammatory response and some may even wind up in the blood circulation, causing systemic effects.
The eicosinoids produced by EPA, most significantly prostaglandins and leukotrines, are considered to be anti-inflammatory in nature because they are significantly less potent (roughly 10x less than those produced by AA), are anti-aggregatory, and are less vasoconstrictive. For this reason, EPA can be used to modify or blunt the inflammatory response of the body’s neutrophils, making it useful for a myriad of health conditions where anti-inflammatory processes are needed.
COMPETITION BETWEEN FATTY ACIDS
One of the most important things to consider when formulating a diet is that omega-6 and omega-3 fatty acids compete with each other for the same metabolic pathways and enzymes. What this means, a little more broken down: when a cellular membrane is damaged and releases a fatty acid, that fatty acid is then metabolized into an eicosanoid- either produced by AA, or EPA. This is where the role of dietary manipulation of omega fatty acids comes into play!
By supplementing additional EPA, we can manipulate the fatty acid composition of the cells, allowing EPA to essentially “win” as the fatty acid that the damaged cell releases and metabolizes. This will decrease the amount of pro-inflammatory eicosanoids produced by AA, increase the amount of less-potent eicosanoids by EPA, increase the amount of anti-inflammatory resolvins, and “hit the brakes” on the body’s inflammatory response.
In canine diets, the amount of omega-6 fatty acids versus the amount of omega-3 fatty acids is generally expressed as a ratio, i.e. 10:1. The majority of kibble has ratios 15:1 and higher. For fresh diets, the ideal ratio for the healthy dog is 2:1 through 4:1, and ideally no higher than 7-8:1.
It is sometimes said that this ratio cannot be relied on because it takes into consideration not just EPA and DHA but also ALA; however, it is completely possible to determine the ratio while excluding ALA. All Fed to Thrive clients receive their recipe’s omega-6:omega-3 ratio, and that ratio takes into account LA, AA, EPA, and DHA.
THERAPEUTIC APPLICATION OF FATTY ACIDS
The supplementation of omega-3 fatty acids is commonly used in acute and chronic conditions and diseases where modification of the body’s inflammatory response is required. This includes, but isn’t limited to:
Canine cognitive disorder
Soft tissue trauma
NEGATIVE EFFECTS OF SUPPLEMENTATION
Gastrointestinal effects like mucus in the stool, soft stool, or diarrhea can occur when large doses of fatty acids are dosed or when moderate doses are given to a dog with a sensitive gastrointestinal tract. Owners should always begin slowly, increasing to the desired amount over a period of several days.
Slow wound healing can occur if the dog’s inflammatory process is very inhibited; the inflammatory process is required for normal wound healing. However, the ratio of omega-6:omega-3 fatty acids needed to achieve this effect in a laboratory setting was 0.3:1, a much higher ratio of omega-3 fatty acids than what the normal dog would ingest. However, due to the possibility of slow wound healing, high doses of omega-3 fatty acids should be stopped a week before any surgery. Better to be safe!
Exposure to heavy metals from oily fish and fish oil is occasionally mentioned but is generally not cause for concern if small, oily fish are used (tuna, swordfish, shark, etc. should always be avoided) and if a fish oil is used from a reputable company.
Excessive vitamin A and vitamin D3, fat-soluble vitamins that accumulate within the liver, can cause toxicity in dogs. For this reason, I do not recommend supplementing using cod liver oil in a regular ratio-based fresh food diet.
WHAT IS PERIOXIDATION?
Polyunsaturated fatty acids are highly susceptible to lipid perioxidation. Lipid perioxidation is the process of free radicals- highly volatile molecules that quickly react with other atoms or molecules because they are missing electrons- taking electrons from the lipids (fats, or in this case polyunsaturated fatty acids) in cell membranes, which results in cell damage and a domino effect. The domino effect occurs because once the original fatty acid has been effected, it then loses its stability and continues the cycle, creating free radical after free radical, a process called oxidative stress. While some oxidative stress is inevitable, long-term oxidative stress will damage the cells and DNA, cause chronic inflammation, and contribute to neurodegenerative diseases and aging.
To prevent oxidative stress, we provide the body with antioxidants, which are compounds that sacrifice themselves by binding to free radicals. When I say “sacrifice”, I mean that a continuous supply of them is needed because they don’t simply destroy a free radical and move on!
Healthy dogs can produce their own antioxidant in the form of vitamin C, but vitamin E is a powerful antioxidant that is an essential nutrient (meaning it must be provided in the diet). The more polyunsaturated fatty acids (PUFAs) we add, the more E we must add; it’s needed for both omega-6 and omega-3 fatty acids, but more vitamin E is needed for DHA and EPA (in that order) than other fatty acids. The biologically active and potent form of vitamin E is called d-alpha-tocopherol and should be provided in a concentrated, naturally-derived form.
A good rule of thumb is 2 IU of vitamin E for every pound of dog. For example, a 50-pound adult dog would receive 100 IU of vitamin E a day.
When omega fatty acids are supplemented or when the body is exposed to cell irritants, vitamin E becomes rapidly depleted. During times of stress, illness, increased PUFA supplementation, etc. it should be provided every day.
RECOMMENDED BRANDS & DOSING
Generally speaking, for a dog at maintenance- that is, a dog who does not need therapeutic doses of fish oil- the recommended dosage based on weight can be found on the bottle for the product that you are using.
There is no single consensus on exactly how much should be given a day, but 40-70 mg combined EPA + DHA per kilogram of body weight is a safe dose for a dog.
The National Research Council (NRC) has established a safe upper limit for combined amounts of EPA + DHA for the dog: 2,800mg per 1,000 kcals of diet or 370 mg x kg^0.75 a day. For example, a 50-pound dog (22.7 kg) could have a maximum of 3,848 mg/day of combined EPA + DHA.
My go-to brands are Nordic Naturals for medium to large breed dogs, and Bonnie & Clyde for small breed dogs. This preference is based on brand quality and ethics, as well as ease of dosing.
ALTERNATIVES TO FISH & FISH OILS FOR INTOLERANT DOGS
Occasionally, dogs will be intolerant or allergic to oily fish, which can certainly make it more difficult to provide EPA and DHA! Luckily, several other options do exist:
- Krill oil, which contains both EPA and DHA, is highly bioavailable and may not elicit the same reaction as fish oil.
- Algae oil, which contains both EPA and DHA, is an option, although bioavailability may be lower in dogs
- Phytoplankton is occasionally touted as being better than fish oil- only certain species contain both EPA and DHA, and not in the same concentrations as marine oil; this would be best paired with a separate source of DHA
- Brain tissue such as pork or lamb brain contains concentrated amounts of DHA, but is also quite fatty overall. I like to pair brain with phytoplankton in fish-intolerant dogs!
Links to krill oil, algae oil, and phytoplankton can be clicked on their respective names above. These are not affiliate links.
I often see pet parents wanting to utilize plant-based oils like flaxseed or hempseed oil to provide omega-3 fatty acids because they have read that these products are high in omega-3s. While this is technically true, remember that plant-based sources only provide, alpha-linolenic acid (ALA), which dogs do not efficiently convert to EPA, and which they cannot convert to DHA.
Remember: coconut oil, hempseed oil, flaxseed oil, chia seeds, etc. are not interchangeable with marine sources.