Veggie versus meat diets for cats and dogs: nutritional considerations

Dr Andrew Knight and Dr Madelaine Leitsberger provide a balanced view of the issues with vegan and meat-based foods for dogs and cats, and what we should do about it.

"Guardians should do all they can to ensure diets are nutritionally complete and reasonably balanced. Regardless of dietary choice, consumers should be encouraged to check labelling claims of nutritional adequacy, and to ask manufacturers what steps they take, and what evidence they can provide, to ensure nutritional soundness and consistency of their diets."

In 2015, Kanakubo and colleagues published a study in the Journal of the American Veterinary Medical Association, demonstrating that a range of commercially available vegetarian(1) diets for cats and dogs had nutritional deficiencies. After analysing 13 dry and 11 canned vegetarian diets for dogs and cats sold within the United States, they concluded that 25% (6/24) diets did not meet all amino acid minimum requirements specified by the Association of American Feed Control Officials (AAFCO), although overall protein content was not a concern. The AAFCO nutrient profiles are based on those of the National Research Council of the National Academy of Sciences – which is the leading provider of nutrient recommendations for dogs and cats.

On the face of it, this appears to raise significant concerns for canine or feline guardians who wish to maintain their companions on vegetarian diets. Amino acids (AAs) are the building blocks of proteins, and indeed, much of our bodies. AAs such as taurine, carnitine, methionine, lysine and tryptophan are used for a wide variety of bodily functions, and deficiencies will eventually result in nutritional diseases (Armstrong et al. 2010). 

Should we use meat-based diets instead?

"Metabolisable energy (ME) density increases [in meat-based foods] were substantial, meaning animals were consuming far more than they needed. Such errors could partly explain increasing and concerning rates of obesity and a range of other diseases and illnesses in modern companion animals."

Does this mean all who use such diets should immediately switch to meat-based diets? Not necessarily – because meat-based diets do not seem to be any safer.

Hill and colleagues (2009) utilized the ‘sample check program’ offered by five U.S. states(2) to compare labelling guarantees of nutritional content, and actual nutritional content — as determined via laboratory analysis – of 2,208 pet foods manufactured by 204 companies. Included were 1,158 canned foods, 750 dry foods, 258 treats, 32 other types of foods (soft-moist, soft-dry, liquid, supplemental, or foods in pouches), and 21 foods of unidentified types. 

Variations between labelling claims and measured values were common. Hill and colleagues noted that, “In absolute terms, the mean differences in analyses were mostly small. However, as a percentage of the amounts of each nutrient in the diet, the mean changes were substantial (5%–30%). Such inaccuracy can substantially affect any estimate of the ME density of the food…”. Metabolisable energy (ME) density increases were substantial, meaning animals were consuming far more than they needed. Such errors could partly explain increasing and concerning rates of obesity and a range of other diseases and illnesses in modern companion animals (Larsen et al. 2016). Hill and colleagues also noted that, “Within all types of food, there were a few outlying values where actual food analyses diverged markedly from the guarantee. For such foods, the adjusted estimate of composition would remain wildly inaccurate”. 

In 2016 we published our survey of the 12 U.S. companies studied by Kanakubo and colleagues, providing additional information from these manufacturers about the steps they’d taken to try to ensure the nutritional adequacy of their diets. We also reviewed all of the other studies in this field that we could locate. It is clear that although ongoing concerns exist about the nutritional adequacy of vegetarian companion animal diets, these concerns are not limited to such diets, and include a wide range of meat-based companion animal food products. Indeed, it is highly likely that repeated independent laboratory analyses of a range of commercial products, vegetarian or meat-based, would demonstrate nutritional inadequacies and inconsistency of nutritional content over time. Such concerns probably apply to most of the diets that cats and dogs are maintained on today.

"It is clear that although ongoing concerns exist about the nutritional adequacy of vegetarian companion animal diets, these concerns are not limited to such diets, and include a wide range of meat-based companion animal food products."

Health of vegetarian and carnivorous cats and dogs

How concerned should we be about such problems? Our study also reviewed the existing evidence about the health of cats and dogs maintained on vegetarian diets, and compared them with their carnivorous counterparts. It is clear that cats and dogs maintained on nutritionally reasonable vegetarian diets may be healthy — including those exercising at the highest levels — and, indeed, may experience a range of health benefits. Such diets also avoid a range of hazards common within meat-based diets. 

However, guardians should do all they can to ensure diets are nutritionally complete and reasonably balanced. As we have stated (2016), “Regardless of dietary choice, consumers should be encouraged to check labelling claims of nutritional adequacy, and to ask manufacturers what steps they take, and what evidence they can provide, to ensure nutritional soundness and consistency of their diets.” Guardians should also regularly monitor urinary acidity and correct any urinary alkalinisation that may occur, through appropriate dietary additives. These issues are described in our 2016 article and at www.vegepets.info.

Commercial meat-based diets typically contain a range of body parts from animals that cats and dogs would never naturally consumes, such as cows, sheep, pigs, turkeys, ducks, chickens, fish and prawns. We’ve discussed the implications of natural feeding behaviour for meat-based and vegetarian companion animal diets in a previous article. Detailed additional information, including advice on safely transitioning cats and dogs to vegan diets, can be found at in our 2016 article and at www.vegepets.info.

By Veterinary Professor Andrew Knight and Madelaine Leitsberger at the Centre for Animal Welfare, University of Winchester.

Notes and references

(1) In this article, the term vegetarian is routinely used, although many of the people and animals referred to are, in fact, vegan.

(2) South Dakota, Indiana, New York, New Jersey, and Rhode Island.

• Armstrong, P.J.; Gross, K.L.; Becvarova, I.; Debraekeleer, J. Introduction to feeding normal cats. In Small 
Animal Clinical Nutrition; Hand, M.S., Thatcher, C.D., Remillard, R.L., Roudebush, P., Novotny, B.J., Eds.; 
Mark Morris Inst.: Topeka, KS, USA, 2010; 371–372. 


• Kanakubo, K.; Fascetti, A.J.; Larsen, J.A. Assessment of protein and amino acid concentrations and labeling 
adequacy of commercial vegetarian diets formulated for dogs and cats. J. Am. Vet. Med. Assoc. 2015, 247,
385–392. 


• Knight, A.; Leitsberger, M. Vegetarian versus Meat-Based Diets for Companion Animals. Animals 2016, 6, 57.

• Larsen, J.A.; Villaverde, C. Scope of the problem and perception by owners and veterinarians. Vet. Clin. N. 
Am. Small Anim. Pract. 2016, 46, 761–772.