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Are grains unhealthy for pets?



Grain-free diets are one of the largest growing segments of the pet food market. More and more pet owners are reaching for these diets, which are sometimes billed as more natural for pets, with less fillers, less carbs and less likely to cause allergies.

So is this true? Are grain-free diets indeed better for pets? Before we come to any conclusion, let’s first explore the science1,2,3.

Firstly, what is a filler? A filler is considered an ingredient with little or no nutritional value. Is it legitimate to label grains as fillers? Grains contribute valuable nutrients to the diet including vitamins, minerals, antioxidants, essential fatty acids and fibre, all essential for health. Grains are definitely not fillers.

Are grain-free diets more ‘natural’? Do they help feed our pets like their wild ancestors?

Dogs most likely originated from wild wolves; however the precise timing is unclear. They are thought to have been domesticated somewhere around 12,000 and 33,000 years ago 4,5. The domestic dog of today is vastly different phenotypically and biologically from its ancestral wolf. In fact dogs and cats have evolved alongside humans to be able to digest grains as well as many other sources of carbohydrates. What’s more, grains used in pet foods undergo processing, such as grinding, cooking and extrusion, making them highly digestible6. It could be argued that substituting grains for highly refined starches like potatoes, sweet potatoes, tapioca (cassava), peas or lentils  is no more ‘natural’ a diet for a wolf to consume. These foods may contain as much and sometimes more carbohydrate as grain-containing diets.  What’s more, these ingredients often provide fewer nutrients and less fibre than whole grains.


Another  confusion is that both wolves and dogs belong to the taxonomic Order Carnivora, which often gets confused with thinking dogs are carnivorous. While these animals all share a dental structure that originally evolved for shearing meat, most of the species in Carnivora are now omnivores (skunks, raccoons, bears, etc.) and a few are completely or almost completely herbivorous like the Giant Panda which only consumes bamboo!


Cats on the other hand, are considered obligate carnivours in that they have a requirement for nutrients present only in animal tissue within their diet. That said, while cats do require part of their protein to come from animals, their systems are also very good at digesting and absorbing nutrients from high-quality, plant-based ingredients7.

Are grain-free diets more ‘natural’? Do they help feed our pets like their wild ancestors?

While food allergies in pets are uncommon, accounting for 1% of skin disease or less than 10% of allergic skin disease in dogs8, allergies to grains are even rarer.  Because allergies are abnormal or inappropriate reactions of the immune system against a normal protein, they can form to any protein or protein-containing food or ingredient. However, the small numbers of pets that do have allergies are most likely to be allergic to animal proteins. In dogs the commonest reported food allergens are beef, dairy and chicken and in cats are beef, dairy and fish8,9.  This list reflects how common these ingredients have traditionally been in commercial diets rather than an increased tendency to cause allergies. As grains do contain protein, allergies to grains such as wheat can occur. However, reactions to other grains and carbohydrate sources, such as rice, corn, and potato are very uncommon. If a dog or cat has a diagnosed food allergy, treatment involves feeding either a hydrolysed diet or a food containing a single protein and carbohydrate source which they have not been previously exposed to. These are called novel protein and carbohydrate diets. Take care when choosing a food claiming to be hypoallergenic or novel. While they may only have one protein and carbohydrate source mentioned on the front of the pack, on closer examination of the ingredient list you may find several other sources of both.


Some pet owners cite the potential for gluten sensitivity as the reason for avoiding grains in their pet’s food. Celiac disease in humans is a heritable autoimmune disease associated with hypersensitivity to gluten proteins in wheat and other related grains such as barley and rye. Corn gluten and rice gluten, on the other hand, are quite different from wheat gluten and can be consumed by most celiac patients without concern. Gluten intolerance is also exceedingly rare in pets, with gastrointestinal signs from consuming gluten having only been observed in a small number of dogs, including some Irish Setters.

So back to our original question, are grains unhealthy for pets?

The answer is no, there is no evidence that grains are nutritionally harmful to pets. There are many good quality commercial pet foods available both with, and without grains.


The most important things to look for in a food is that the food provides  high-quality, highly digestible, complete and balanced nutrition and that is formulated for the correct life-stage. For example, if a food is formulated for ‘growth and maintenance’ or for ‘all life stages’, it means that the food must meet the nutrient requirements for the most demanding life stage, a growing puppy or kitten. Such diets are unlikely to be ideal for an adult dog or cat and definitely not for a senior pet.


It’s also important to remember that ingredients are included in pet foods primarily as a source of nutrients. Animals require specific nutrients such as amino acids from protein and glucose from carbohydrate, not specific ingredients.


Finally, consideration should be given to the longevity and history of the manufacturing company, their commitment to continual research and development, along with the approachability and ethical culture of the company when deciding to feed a particular food,  not just whether the food contains grain or not.

Dr Delisa Appleton BVSc (Hons) PhD. Professional Consulting Veterinarian, Hill’s Pet Nutrition.

Delisa graduated from the University of Queensland with honours in 1987 after which she worked in mixed and small animal veterinary practice for 7 years before commencing work in the nutrition industry.  She then returned to the University of Queensland in 1999 to undertake research with Prof. Jacquie Rand into nutritional aspects of obesity and diabetes in cats She has had numerous papers and reviews published and was awarded a PhD in nutrition in 2004.

Dr Delisa Appleton


  3. Laflamme D, Izquierdo O, Eirmann L, Binder S. Myths and misperceptions about ingredients used in commercial pet foods. Vet Clin North Am Small Anim Pract. 2014;44:689-698.
  4. Ovodov, N. D. et al. A 33,000-year-old incipient dog from the Altai mountains of Siberia: evidence of the earliest domestication disrupted by the last glacial maximum. PLoS ONE 6, e22821 (2011)
  5. Davis, S. J. M. & Valla, F. R. Evidence for domestication of the dog 12,000 years ago in the Natufian of Israel. Nature 276, 608–610 (1978)
  6. Murray SM, Fahey GC, Merchen RN, et al. Evaluation of selected high-starch flours as ingredients in canine diets. J Anim Sci 1999; 77:2180-2186.
  8. Verlinden A, Hesta M, Millet S et al. Food allergy in dogs and cats: a review. Crit Rev Food Sci Nutr 2006;46:268
  9. Roudebush P. Ingredients and foods associated with adverse reactions in dogs and cats. Vet Dermatol 2013; 24: 292-294
  10. Hill’s is a trademark of Hill’s Pet Nutrition, Inc. © 2018 Hill’s Pet Nutrition Pty Ltd. HIMA-DA-1819CCAD