Nutritional Myths and Cases That Went Wrong
World Small Animal Veterinary Association Congress Proceedings, 2019
L. Weeth1; G. Takashima2
1Clinical Nutrition, Metropolitan Animal Specialty Hospital, Los Angeles, CA, USA; 2General Medicine, Animal Care Group of Lake Oswego, Lake Oswego, OR, USA


Over the years, awareness of the importance of diet in the maintenance of optimal pet-health has become increasingly appreciated, not only to the veterinary profession, but also in the eyes of the public. Unfortunately, there also is information circulating based on myths or fads and often fear-based, and scientifically unsubstantiated, and seemingly following similar myths and fads in human nutrition.

Nutrient Basics

Animal require nutrients, not ingredients. Sometimes those essential nutrients are found as freely occurring mineral in nature (such as sodium chloride), sometimes those essential nutrients are found only in plants (such as linoleic acid), and sometimes those essential nutrients are only found in other animals (such as taurine). Dogs are classified in the Order Carnivora, but are omnivores in their nutrient requirements, meaning that with proper planning and formulations they can survive and thrive on plant-based diets, whether vegan or vegetarian. Cats, on the other hand, are Carnivora in classification and dietary requirements and need animal-based nutrients in their diet to ensure optimal health.

When evaluating a new diet brand or food type it is important to ensure the diet in question is providing a complete and balanced intake of all essential nutrients, irrespective of the food form. Despite metabolic differences between dogs and cats, they have similar requirements for essential amino acids (dogs have 10 essential amino acids while cats require the same 10+taurine); fatty acids (dogs require the long-chain omega-6 fatty acid linoleic acid [LA] and cats not only require LA but the longer-chain omega-6 arachidonic acid [AA] as well); minerals (though the specific amounts will vary between the two species); water-soluble vitamins (though again the amounts vary between the two); and fat-soluble vitamins.1,2 Some specific adaptations that make dogs and cats different than people include the ability by dogs and cats to synthesize vitamin C in the liver; their inability to create vitamin D from UV exposure no matter how much sunlight they bask in; and their lack of salivary amylase as the initial step in carbohydrate metabolism, but presence of pancreatic amylases and glucose receptors on enterocytes for carbohydrate digestion and absorption.2,3 Altogether dogs require about 37 essential nutrients in their diets to cats 41 and it is important that the diet selected and fed on a regular basis meets these ongoing nutritional needs to prevent disease associated with nutritional deficiencies and to optimal health for longevity.

Some Common Myths and Frequently Asked Questions

I Heard/Read That Grain-Free Diets Are Better and That Grains Are Just “Fillers”

This is what grain-free diet makers and marketers want you to believe, but this is one pet food myth that is false. Dogs and cats require nutrients, not ingredients, and unless an individual animal has an allergy (rare) or intolerance (still uncommon, but more prevalent than true allergies) there is no proven benefit to avoiding grains. Selective pressures over thousands of years have allowed dogs to adapt to a more omnivores diet, and that includes being able to breakdown and digest carbohydrates from properly cooked grains readily. Avoiding high intake of carbohydrate for an otherwise health adult cats in general is recommended, no matter if that carbohydrate comes from grains, potatoes, or legumes as these obligate carnivores are less efficient at digesting plant-based ingredients.

Dogs and cats can digest cereal grains in species appropriate amounts as long as they are properly cooked and the overall diet is nutritionally balanced. Every ingredient in a pet food must have a purpose, whether nutritionally (cereal grains provide energy in the form of carbohydrates as well as nutrients such as essential fatty acids, vitamins and minerals). Cereals also provide dietary fiber that while considered “non-essential” in the diet is functionally essential for optimal intestinal function. True “fillers” in pet foods are things like chamomile, dandelion, and blueberry that are in such small amounts or have been so highly processed that any phytonutrients are long denatured before the diet is fed. These are used as “label filler” to appeal to people and provide little to no health benefit to dogs or cats.

In addition, there is currently an ongoing investigation by the Food and Drug Administration Center for Veterinary Medicine (FDA-CVM) and a number of veterinary universities in the United States looking into links between grain-free diets and dilated cardiomyopathy (DCM) in dogs. Until the causative link between feeding grain-free diets and DCM is determined, going “grain-free” may actually cause more harm than good for some patients.

I’m a Vegan/Vegetarian, Can I Feed a Similar Diet Strategy to My Dog or Cat?

For dogs, going vegetarian (a plant-based diet that still includes egg and/or dairy) is pretty easy as egg has a complete amino acid profile and for an adult, non-reproductive dog, dairy works quite nicely, too. Vegan diets (avoiding all animal-sourced ingredients) is a bit trickier, but not impossible. Dogs are able to manufacture adequate amounts of taurine from methionine and cysteine (though breed and diet factors may alter this), can split ½-carotene from root vegetables and fruit into vitamin A, and are also able to convert LA found in plant seeds and grains into AA.1 Cats have unique metabolic adaptations that do not allow for transition to completely vegan or vegetarian diets.3 The idea behind feeding vegan/vegetarian diets can be true for dogs, but false for cats.

Ideally a selected vegan or vegetarian diet would have gone through feeding trials (fed to a group of healthy adult dogs to prove that the nutrients in that plant-based diet are digestible and absorbable), but whether this has been done or not, high inclusion of plant-based fibers and ingredients can decrease the overall digestibility of the diet and commercial diets can have variable quality control standards.5,6 Routine checkups (at least annually) should to be performed on any dog eating a vegan or vegetarian diet.

I Heard That “By Products” Don’t Provide Any Real Nutrients into the Diet

Sorry to break it to you, but this is another myth promoted by pet food companies and their marketing departments. The term “by-product” comes from the human food perspective and designates a food that is a secondary product made during the processing or refining of the primary food. Molasses, for example, is the “by-product” of refining sugar; wheat germ is a “by-product’ of wheat milling; and peanut hearts are “by-products” of making peanut butter. When that “by-product” comes from an animal it is specifically referring to the internal organ meats that are left over after the muscle meat is removed for human consumption. These organ meats are edible and highly nutritious, but there is little to no demand for them on the human food market (at least in North America). As such, it is more cost effective and convenient for meat processors to group them together than package them individually. Some pet food companies claim “no by-product” but instead will list out “liver”, “kidney”, “spleen”, “tripe” (stomach), and “lung” individually; these are all by-products.

By-products can come from a single species such as chicken or beef, or a combination of animals such as poultry (chicken, turkey, and/or duck) or meat (beef, pork, lamb, and/or goat). These can only be the edible parts (no hooves, horns, beaks, skin, feathers, or feces allowed) other than the muscle meat. The term “by-product” has no bearing on the nutritional quality of the said ingredient and is often a superior source of essential nutrients in the diet compared to only including muscle meats. Using these highly nutritious “by-products” in dog and cats food also reduces food wastage, is better for the environment (all that unused organ meat would otherwise end up in a landfill or incinerated), and helps reduce the number of food animals that would need to be raised just to provide muscle meat into the pet food production chain.

Other Common Pet Food Myths

  • Home-made diets are better than canned or kibble: References 7–9, false and true (depends on the patient)
  • Home-made diets are easy to make: References 7–9, false (though easy to make wrong)
  • The more expensive diets are the most nutritional: False (most definitely false)


1.  Delaney SJ, Fascetti AJ. Basic nutrition overview. In: Fascetti AJ, Delaney SJ, eds. Applied Veterinary Clinical Nutrition, 1st ed. Ames, IA: John Wiley & Sons, Ltd. 2012:9–22.

2.  Morris JG. Idiosyncratic nutrient requirements of cats appear to be diet induced evolutionary adaptations. Nutr Res Rev 2002; 15:153–168.

3.  Axelson E, et al. The genomic signature of dog domestication reveals adaptation to a starch-rich diet. Nature 2013;495(7441):360–364.

4.  WSAVA Global Nutrition Committee Myths & Frequently Asked Questions:

5.  Kanakubo K, et al. Assessment of protein and amino acid concentrations and labeling adequacy of commercial vegetarian diets formulated for dogs and cats. JAVMA 2015;247:385–392.

6.  Weeth, LP, Chandler, ML, Vegetarian diets. Clinician’s Brief. January 2015;13(1):61–63.

7.  Larsen JA, et al. Evaluation of recipes for home-prepared diets for dogs and cats with chronic kidney disease. JAVMA 2012; 240:532–538.

8.  Heinze CR, et al. Assessment of commercial diets and recipes for home-prepared diets recommended for dogs with cancer. JAVMA 2012; 241:1453–1460.

9.  Johnson LN, et al. Evaluation of owner experiences and adherence to home-cooked diet recipes for dogs. JSAP 2016;57:23–27.


Speaker Information
(click the speaker's name to view other papers and abstracts submitted by this speaker)

G. Takashima
General Medicine
Animal Care Group of Lake Oswego
Lake Oswego, OR, USA

L. Weeth
Clinical Nutrition
Metropolitan Animal Specialty Hospital
Los Angeles, CA, USA

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