Role of Dietary Fatty Acids in Dogs & CatsCE Article
Catherine E. Lenox, DVM, Diplomate ACVN
Royal Canin USA
The American College of Veterinary Nutrition (acvn.org) and Today’s Veterinary Practice are delighted to bring you the Nutrition Notes column, which provides the highest quality, cutting edge information on companion animal nutrition, provided by the ACVN’s foremost nutrition specialists.
The primary objectives of the ACVN are to:
- Advance the specialty area of veterinary nutrition
- Increase the competence of those practicing in this field
- Establish requirements for certification in veterinary nutrition
- Encourage continuing education for both specialists and general practitioners
- Promote evidence-based research
- Enhance dissemination of the latest veterinary nutrition knowledge.
The ACVN achieves these objectives in many ways, including designating specialists in animal nutrition, providing continuing education through several media, supporting veterinary nutrition residency programs, and offering a wide array of resources related to veterinary nutrition, such as this column.
Dietary fats, as well as specific fatty acids, are essential in the diet of dogs and cats, as recognized in the nutrient recommendations for pet food provided by the National Research Council (NRC) and the Association of American Feed Control Officials (AAFCO).1,2 Fats and fatty acids:
- Provide energy
- Aid in fat-soluble vitamin absorption
- Modulate inflammation
- Act as a precursor to eicosanoids and prostaglandins
- Serve structural roles as a component of cell membranes
- Promote healthy growth and development
- Affect skin and coat health.1
The type of fatty acids fed to a patient, as well as the total amount of fatty acids in the diet, have the additional potential to improve or impair health. This review discusses basic properties of fatty acids; sources of essential fatty acids; therapeutic modifications of dietary fatty acids, fish oils, and other fatty acid supplements; and areas of caution in clinical practice when supplementing fatty acids.
The American College of Veterinary Nutrition (ACVN) is a small specialty college, with members working in private practice, academic veterinary medicine, and industry. Board-certified veterinary nutritionists in industry regularly contribute to the academic mission of the College through research publications, conference presentations, continuing education efforts, and active membership. As a result, these specialists, like Dr. Lenox, may be invited to author articles on topics within their area of expertise when there is no conflict of interest.
Potential conflicts of interest are reviewed by myself as guest section editor, a peer reviewer (who is a member of ACVN and not employed by the same organization as the author), and the administrative/editorial team at Today’s Veterinary Practice. No special advertising consideration is provided to industry companies for whom authors may work.
The goal of this column is to provide the latest in unbiased and evidence-based veterinary nutrition from the foremost experts irrespective of their places of employment. We, as always, welcome your feedback on the column and hope the material herein proves of value in your practice.
—Justin Shmalberg, DVM, Diplomate ACVN & ACVSMR, CVA, CVCH, CVFT
ACVN Liaison to Today’s Veterinary Practice
BASIC PROPERTIES OF FATTY ACIDS
Fatty acids are classified as lipids, a larger macronutrient class that serves a structural role and provides energy, among other functions. Lipids include phospholipids and cholesterol as well as fats, oils, and fatty acids.
Classification of Fatty Acids
The functions of different fatty acids depend on their structure and composition. Fatty acids are classified based on:
- Length of the hydrocarbon chain
- Number of double bonds present in the chain
- Location of the first double bond relative to the methyl, or omega, end of the hydrocarbon chain (Figure).
Fatty acids are considered short-chain (< 8 carbons in length), medium-chain (8–12 carbons), or long-chain (> 12 carbons). The number of carbons in the chain gives the fatty acid different properties in terms of digestion, absorption, and usage.1
Fatty acids are further defined by the number of double bonds: saturated fats contain no double bonds, monounsaturated fats contain 1 double bond, and polyunsaturated fats contain 2 or more double bonds.
Fatty acids with double bonds are called omega-9, omega-6, or omega-3 based on the location of the first double bond from the methyl (omega) end of the hydrocarbon chain. For example, omega-6 fatty acids, often found in animal tissue and in sunflower and safflower oils, have their first double bond between carbons 6 and 7 from the omega end, whereas omega-3 fatty acids, derived from plant and marine sources, have their first double bond between carbons 3 and 4.
Essential Fatty Acids
Dogs and cats require omega-6 and omega-3 fatty acids in the diet because they cannot produce these essential fatty acids on their own.1 Essential fatty acids and their numeric formulas are listed in Table 1.
The omega-6 essential fatty acids are linoleic acid (LA, containing 18 carbons with 2 double bonds [18:2]) and arachidonic acid (AA, 20:4). LA is essential for both dogs and cats, whereas AA is essential only for cats. Cats require AA due to the lack of delta-6 desaturase, an enzyme required for endogenous conversion of LA to the longer and more unsaturated fatty acid AA.3
It is important to note that these omega-6 fatty acids cannot be endogenously produced in sufficient quantities. They must be provided in the diet to prevent signs of deficiency. Deficiency of omega-6 fatty acids can cause skin and coat abnormalities, reproductive problems, and failure to thrive.1
The omega-3 essential fatty acids are alpha-linolenic acid (ALA, 18:3), eicosapentaenoic acid (EPA, 20:5), and docosahexaenoic acid (DHA, 22:6). EPA and DHA are found primarily in marine sources, including fish oil as well as phytoplankton and other marine plants.
As a result of the poor conversion of ALA to EPA and DHA,4-7 the NRC lists dietary requirements for EPA and DHA for both dogs and cats.8 However, requirements vary among different life stages; for example, growing puppies and kittens require more DHA than adult dogs and cats. Omega-3 fatty acid deficiency may result in neurologic abnormalities, such as decreased visual acuity.1
ESSENTIAL FATTY ACIDS IN THE DIET
It is recommended that all pet food provide essential omega-6 and omega-3 fatty acids. Minimum requirements for total fat, LA, ALA (except for adult cats), EPA + DHA, and AA are published by the NRC, and minimum requirements for the concentration of crude fat, LA, ALA, AA (cats only), and EPA+DHA in pet food are listed in the AAFCO nutrient profiles.2,8 These minimum requirements are listed in Table 2.
Sources of Essential Fatty Acids
Sources of LA and ALA are plant-based oils, including corn oil, soybean oil, canola oil, and flaxseed oil. AA is found typically in animal fat, with little to no AA present in plant oils and seeds.1
As of 2016, EPA and DHA are described in AAFCO nutrient profiles for growth and reproduction, and the NRC lists these fatty acids as essential. As a result, many pet foods contain sources of EPA and DHA. Fish oil is the main dietary source of EPA and DHA.
Common oils used in pet food and their saturated and essential fatty acid content can be found in Table 3. More information regarding sources of essential fatty acids can be found elsewhere.9
Quality of Supplement
If supplementing a diet with fatty acids, it is important to choose a quality supplement. When choosing a fish oil supplement, take special care to select one from a reputable company with good quality control practices. Potential exists for nutrient excess (mainly vitamins A and D) and toxin exposure, including mercury exposure with fish oil supplements.10 Calling a manufacturer to inquire about quality control testing and consulting an independent (third party) evaluator are 2 ways to ensure the supplement quality.
DIETARY FATTY ACIDS: BODY CONDITION & DISEASE
Dietary fat levels can be adjusted to help manage disease. Adjusting the amount of dietary fat and specific fatty acids can also affect the energy density of a pet food.
For Body Condition
At 8.5 kcal/g, dietary fat is more than twice as energy dense as protein and carbohydrate (each 3.5 kcal/g).11
- Higher fat diets (when tolerated) can increase the energy density of a diet, aiding in weight gain without significantly increasing the volume of food needed to improve body condition.
- Lower fat diets, which are lower in energy density, can help with weight loss, while providing required essential fatty acids and allowing a patient to consume a larger volume of food without significantly increasing caloric intake.
For Disease: Fat Restriction
Not all patients can tolerate average amounts of dietary fat. Managing conditions, such as hyperlipidemia, canine pancreatitis, and lymphangiectasia, often necessitates dietary fat restriction (< 20% of total calories from fat).12-14 In some patients, therefore, dietary fat restriction is used as an adjunct therapy in disease management, despite the animal’s body condition and the desired energy density for its diet.
Before implementing fat restriction, however, a dietary history should be obtained (Table 4). This helps ensure that, when the patient’s nutritional plan is adjusted, dietary fat is restricted relative to the previous diet. It is also imperative that essential fatty acid requirements be met despite fat restriction. A low fat diet can be provided that meets fatty acid requirements, with most dietary fat coming from essential fatty acids, including LA, ALA, AA, EPA, and DHA.
Overall, a nutritional assessment and plan should ensure adequate energy and nutrient intake for the patient despite fat restriction. A thorough nutritional assessment includes assessment of animal factors, dietary factors, and feeding management and environmental factors.15
For Disease: Supplementation
Fatty acids, especially EPA and DHA, have a number of therapeutic uses in dogs and cats that are summarized elsewhere.
- Supplemental fish oil is used as adjunctive therapy for inflammatory conditions, such as inflammatory skin disease and osteoarthritis, cancer, hyperlipidemia, and cardiac disease.16
- DHA is supplemented in growth diets to support optimal retinal function and neuronal development.17
- Supplementation with fatty acids, including LA and EPA/DHA, is used to treat dermatologic disease.1,18,19
If fatty acid supplementation is indicated, a full clinical assessment, including medical and dietary history and physical examination, is necessary to determine the most appropriate fatty acid supplement for the patient.
FISH OIL SUPPLEMENTATION & DOSING
Fish oil is a commonly used supplement in dogs and cats and is added to many pet foods. Some manufacturers supplement with flaxseed oil, which is a rich source of ALA, instead. However, the conversion rate of ALA to EPA is very low in dogs, and production of AA and EPA from LA and ALA, respectively, is virtually zero in cats due to low activity of the enzyme delta-6 desaturase.3,4,6
Therefore, if the goal is therapeutic supplementation of specific fatty acids, such as omega-3s, those particular fatty acids likely need to be provided in the diet. For example, the most efficient way to increase EPA and DHA in a pet’s diet is to provide these fatty acids in a supplemental form, such as fish oil. It can be challenging, however, to supplement EPA and DHA in the form of fish oil capsules to large dogs because EPA and DHA concentrations in standard fish oil capsules are not extremely high.
Several methods can be used to calculate a dose for a fish oil supplement, and there is no consensus on the most appropriate way to dose EPA and DHA. Fish oil can be dosed as:
- Milligrams EPA + DHA (combined) per kg body weight (body weight0.75) or per kg metabolic body weight (body weight0.67)
- Grams per 100 g of food on an as fed or dry matter basis
- Grams per 1000 or 100 kcal of diet fed
- An omega-6 to omega-3 ratio.20
Although more research is needed to determine the most appropriate dose and dosing method, I typically dose fish oil at:
- Dogs: 50 to 75 mg EPA + DHA (combined) per kg body weight
- Cats: 30 to 50 mg/kg.
Considerations of Supplementation
When recommending fish oil supplementation for a patient whose food already contains EPA and DHA, consider reducing the dose of supplemental fish oil. Some diets, such as those designed for skin or joint disease, contain significant quantities of EPA and DHA. With these diets, additional supplementation of EPA and DHA may exceed the NRC safe upper limit for a particular patient, and could be potentially harmful.
On the other hand, not all diets or supplements that contain “omega-3 fatty acids” include EPA or DHA. Therefore, reading the ingredient list or supplement information is necessary. In many cases, it may be necessary to call a manufacturer to get the EPA, DHA, and ALA concentrations in a diet or supplement.
Recommended Allowances & Upper Limits
The NRC has established an adequate intake and a recommended allowance for EPA + DHA for all canine and feline life stages. In addition, a safe upper limit of 2.8 g EPA + DHA per 1000 kcal has been established for puppies, adult dogs, and reproducing dogs. No safe upper limit has been published for cats at any life stage.8 Therefore, I use more caution when supplementing EPA and DHA to cats.
Table 5 provides examples of adequate intake, recommended allowance, and safe upper limit for an adult dog weighing 10 kg and an adult cat weighing 5 kg, in addition to suggested total EPA + DHA doses for patients requiring fish oil supplementation.
AREAS OF CAUTION IN CLINICAL PRACTICE
Although fatty acids are essential nutrients and provide many benefits to dogs and cats, providing too much dietary fat or excessive fish oil supplementation can have detrimental effects:
- In patients in which dietary fat restriction is recommended—such as those prone to hyperlipidemia or other diseases associated with fat intolerance—supplementation of additional fatty acids could be detrimental.
- Omega-3 fatty acid supplementation can result in potential adverse effects, including gastrointestinal signs (ie, vomiting or diarrhea), decreased platelet aggregation, alterations in immune function, decreased wound healing, and nutrient–drug interactions.10
Due to the potential for detrimental effects, use caution when recommending high fat diets or fish oil supplements in certain patients.
Use high fat diets with caution in patients that:
- Are overweight or obese (due to high calorie content of dietary fat and fatty acid supplements)
- Have fat-intolerant conditions, such as hyperlipidemia, canine pancreatitis, or lymphangiectasia.
Use caution when recommending fish oil supplements in patients:
- With thrombocytopenia, large or nonhealing wounds, or gastrointestinal disease
- Receiving drugs that alter platelet function, such as aspirin.10
Although numerous studies have investigated the potential benefits of fatty acid supplementation, the appropriate type of fatty acid and dose of the supplement are dependent on the patient, history, clinical signs, and concurrent diseases. For multiple reasons, what is appropriate for one patient may not be appropriate for another.
Before supplementing a patient with either omega-6 or omega-3 fatty acids, it is important to note that supplements, including fatty acid supplements, can have adverse effects. In addition, although certain patients may benefit from omega-3 and/or omega-6 fatty acid supplementation, most commercial diets contain these fatty acids, albeit at varying levels.
Therefore, before supplementing any patient with fatty acids, be sure to get a full diet history and conduct both a clinical and nutritional assessment to determine the best nutritional plan.
AA = arachidonic acid; AAFCO = Association of American Feed Control Officials; ALA = alpha-linolenic acid; DHA = docosahexaenoic acid; EPA = eicosapentaenoic acid; LA = linoleic acid; NRC = National Research Council
- National Research Council. Fats and fatty acids. Nutrient Requirements of Dogs and Cats. Washington, DC: The National Academies Press, 2006, pp 81-110.
- Association of American Feed Control Officials. Model bill and regulations. 2016 Official Publication. Champaign, IL: Association of American Feed Control Officials, Inc, 2016, pp 107-240.
- Rivers JP, Sinclair AJ, Crawford MA. Inability of the cat to desaturate essential fatty acids. Nature 1975; 258(5531):171-173.
- Bauer JE. Metabolic basis for the essential nature of fatty acids and the unique dietary fatty acid requirements of cats. JAVMA 2006; 229(11):1729-1732.
- Bauer JE, Dunbar BL, Bigley KE. Dietary flaxseed in dogs results in differential transport and metabolism of (n-3) polyunsaturated fatty acids. J Nutr 1998; 128 (12 Suppl):2641S-2644S.
- Filburn CR, Griffin D. Canine plasma and erythrocyte response to a docosahexaenoic acid-enriched supplement: Characterization and potential benefits. Vet Ther 2005; 6(1):29-42.
- Pawlosky RJ, Denkins Y, Ward G, et al. Retinal and brain accretion of long-chain polyunsaturated fatty acids in developing felines: The effects of corn oil-based maternal diets. Am J Clin Nutr 1997; 65(2):465-472.
- National Research Council. Nutrient requirements and dietary nutrient concentrations. Nutrient Requirements of Dogs and Cats. Washington, DC: The National Academies Press, 2006, pp 354-370.
- Lenox CE. Timely topics in nutrition: An overview of fatty acids in companion animal medicine. JAVMA 2015; 246(11):1198-1202.
- Lenox CE, Bauer JE. Potential adverse effects of omega-3 fatty acids in dogs and cats. J Vet Intern Med 2013; 27(2):217-226.
- National Research Council. Energy. Nutrient Requirements of Dogs and Cats. Washington, DC: The National Academies Press, 2006, pp 28-48.
- Villaverde C. Nutritional management of exocrine pancreatic diseases. Applied Veterinary Clinical Nutrition. West Sussex, UK: John Wiley & Sons, LTD, 2012, pp 221-234.
- Fascetti AJ, Delaney SJ. Nutritional management of endocrine diseases. Applied Veterinary Clinical Nutrition. West Sussex, UK: John Wiley & Sons, LTD, 2012, pp 289-300.
- Cave N. Nutritional management of gastrointestinal diseases. Applied Veterinary Clinical Nutrition. West Sussex, UK: John Wiley & Sons, LTD, 2012, pp 175-220.
- Baldwin K, Bartges J, Buffington T, et al. AAHA nutritional assessment guidelines for dogs and cats. JAAHA 2010; 46(4):285-296.
- Bauer JE. Therapeutic use of fish oils in companion animals. JAVMA 2011; 239(11):1441-1451.
- Waldron MK, Spencer AL, Bauer JE. Role of long-chain polyunsaturated n-3 fatty acids in the development of the nervous system of dogs and cats. JAVMA 1998; 213(5):619-622.
- Kirby NA, Hester SL, Bauer JE. Dietary fats and the skin and coat of dogs. JAVMA 2007; 230(11):1641-1644.
- Mueller RS, Fieseler KV, Fettman MJ, et al. Effect of omega-3 fatty acids on canine atopic dermatitis. J Small Anim Pract 2004; 45(6):293-297.
- Larsen J. Evidence-based benefits of omega-3 fatty acids for dogs and cats. Proc ACVIM Forum, 2011, pp 555-557.
CE Test: Role of Dietary Fatty Acids in Dogs & Cats
This article is RACE-approved for 1 hour of continuing education credit. To receive credit, take the approved test online at vetmedteam.com/tvp.aspx (CE fee of $5/article).
Upon completion of this article, the reader should be able to recognize the names and classifications of essential fatty acids, discuss the benefits and precautions of dietary fatty acids in small animal veterinary medicine, and give examples of when to use high fat diets or fatty acid supplements and when to avoid them.
This article provides an overview of the roles of fatty acids in canine and feline medicine, including basic properties of fatty acids, sources of essential fatty acids, therapeutic modifications of dietary fat and fatty acids, and areas of caution when supplementing fatty acids.
Questions online may differ from those here; answers are available once CE test is taken at vetmedteam.com/tvp.aspx. Tests are valid for 2 years from date of approval.
1. Which of the following is an omega-6 fatty acid and is essential for dogs?
a. Arachidonic acid
b. Linoleic acid
c. Alpha-linolenic acid
d. Eicosapentaenoic acid
2. True or false: Vegetable oils are a good source of arachidonic acid.
3. Which of the following oils is likely to provide the highest concentrations of essential fatty acids?
a. Coconut oil
b. Corn oil
c. Olive oil
d. Beef tallow
4. Supplementation of which of the following oils has the highest concentration of alpha-linolenic acid?
a. Corn oil
b. Canola oil
c. Flaxseed oil
d. Fish oil
5. True or false: Diet selection should be based on dietary history in addition to the patient’s medical conditions.
6. Which of the following nutrients is the most energy dense?
7. Caution should be used when supplementing fish oil in which of the following types of patients?
a. Thrombocytopenic patients
b. Patients with large non-healing wounds
c. Patients with gastrointestinal disorders such as vomiting or diarrhea
d. All of the above
8. High fat diets should be used with caution in which of the following types of patients?
a. Overweight patients
b. Patients with hyperlipidemia
c. Patients with pancreatitis
d. All of the above
9. Docosahexaenoic acid (DHA) is often supplemented specifically for which types of patients?
a. Puppies and kittens
b. Patients with cancer
c. Patients with dermatologic disease
d. Osteoarthritic patients
10. Which of the following is NOT an essential omega-3 fatty acid?
a. Alpha-linolenic acid
b. Arachidonic acid
c. Eicosapentaenoic acid
d. Docosahexaenoic acid