The Safety of Processed Food

A well-planned, species-appropriate, raw diet provides cats and dogs with the nutrition they need for optimal health.

A poorly-planned raw diet can have quite the opposite effect. For example, meat-only diets will lead to severe mineral imbalances, and mixed diets (raw and processed) can lead to a host of problems via digestive impairment.

As raw diets have come back into popularity, vets have become increasingly concerned for the wellbeing of pets whose owners have received incorrect advice regarding raw feeding. This has led many vets to being unsupportive of raw-feeding, regardless of how it is done.

These vets favour feeding a processed ‘premium’ diet which has been tested by AAFCO (the Association of American Feed Control Officials) to ensure that it provides ‘complete and balanced’ nutrition for cats and dogs. These diets are commonly assumed to provide safe and appropriate nutrition.

AAFCO publishes nutrient profiles for cats and dogs. They base their profiles on the NRC (National Research Council) nutrient guidelines, but tweak them to make it easier for manufacturers to formulate a processed pet food out of ingredients that do not form a natural part of the pet’s diet. A pet food can meet AAFCO accreditation standards in two ways: by providing a nutrient analysis which falls within the AAFCO parameters; or by paying for their food to be AAFCO-tested in a brief feeding trial on a small number of cats and dogs.

AAFCO nutrient profiles are intended to ‘maintain’ a dog or cat without overt nutrient deficiencies developing over a short period of time. Standard veterinary advice is to feed a cat or dog an AAFCO-approved or AAFCO-tested diet in order to meet the ‘complete and balanced’ nutritional needs of the pet.

The majority of vets have confidence that AAFCO accreditation of a food will protect dogs and cats from nutritional disease. An episode of 'Lateline' in Australia described a study published in the Australian Veterinary Journal (2016)1 in which supermarket cat foods were analysed and shown not to contain the nutrient levels stated on the labels.

Studies showing that the contents of a bag of dog or cat food does not match the nutritional analysis on the label are not new. A review of some of these studies makes it hard to accept that processed pet food is anything like the ‘complete and balanced,’ safe, high quality product that their marketers would have us believe.


The study2 featured on the 'Lateline' show analysed 10 wet and 10 dry ‘complete and balanced’ commercial cat foods. They compared the results with the labelling on the packages, and with established dietary requirements (AFFCO and NRC) for cats.

The nutrient compositions and guaranteed analyses listed on the labels failed to match the chemical analyses carried out in the study.

Deficiencies and excesses of various nutrients were found in nearly all the samples, many of which were identified as potentially harmful to cats ingesting the diets.

Studies in the U.S. and New Zealand have found similar problems. In a 2004 study from the Archives of Veterinary Medicine3 33 brands of dry dog food were analysed to see if they met AAFCO standards.

Seven foods had an incorrect calcium:phosphorus ratio. There were inadequacies for potassium (13 foods), zinc (7), iodine (12) and selenium (1). Only 12% (4) of the foods met the minimum requirements for protein, fats and minerals. Five of the deficient foods had passed AAFCO feed trials.

A New Zealand study (1997)4 compared the nutrient composition of 29 wet cat foods (5 budget, 17 premium, 7 super-premium) to the AAFCO cat maintenance nutrient profile.

Nine of the foods did not meet the AAFCO profiles. Five of these contained inadequate taurine. Four contained excessive levels of methionine. Sixty percent of the budget, 18% of the premium, and 43% of the super-premium foods failed to meet AAFCO standards.


Cats and dogs require dietary thiamine (a B vitamin) to stay healthy. Many factors (such as age, genetics, disease, and diet) influence the thiamine requirements of individual cats and dogs. An uncorrected deficiency can be fatal. Thiamine is found naturally in meat products – particularly liver, heart and kidneys.

Thiamine deficiency factors:

  • Inadequate thiamine levels in the diet
  • Heat processing reduces thiamine levels in the food by 50-90%
  • Lack of acidity: many canned foods contain alkalinising gelling agents that reduce acidity and therefore the availability of thiamine
  • Excessive amounts of some types of fish in the diet will inactivate dietary thiamine
  • Sulphite preservatives inactivate dietary thiamine (a serious problem in raw diets that use preservatives)
  • High grain diets reduce thiamine absorption.

A study in the Journal of the American Veterinary Medical Association (2014)5 examined a selection of 90 tinned cat foods (from 45 different brands) – all of them formulated to meet AAFCO nutrient profile standards. Most of the foods were from the US, but four of them were from New Zealand.

Over 13% of the samples had thiamine levels below AAFCO standards, and 15.6% of the samples contained less thiamine than NRC levels (the NRC are considered the benchmark for nutrient level recommendations). The presence of fish in the samples did not affect the likelihood of thiamine deficiency.

Taurine is an amino acid required by cats and dogs for a range of vital functions. Dogs (unlike cats, who rely absolutely on dietary taurine) are able to synthesise taurine. Nevertheless, dogs can still develop taurine deficiency if they have inadequate dietary intake. Taurine is found in abundance in animal-source proteins. Taurine deficiency can be fatal.

Food processing techniques - such as heat, and the addition of fibre - destroy or reduce taurine availability, so manufacturers have to add taurine into their formulations in order to meet required levels. There are two potential problems with this. One: as we have already seen, it is common for processed food to contain lower levels of nutrients than stated on the packaging. And two: both external and individual factors lead to a great deal of variation in the taurine requirements of a cat or dog.

A study in the Journal of the American Veterinary Medical Association (2003)6 looked at a group of Newfoundlands exhibiting a high rate of taurine deficiency despite being fed ‘complete and balanced’ diets.

The authors proposed that certain diets may promote taurine loss in the gastrointestinal tract at a rate which exceeds taurine production. They referenced research in cats that shows taurine losses in the gut are increased by the presence of rice; bran; or low-quality, heat-damaged proteins in the diet.

The authors explained that genetics make some animals more susceptible to deficiency. This means that the ‘complete and balanced’ claim of AAFCO approved or AAFCO tested foods may only be sufficient for maintenance if a pet is fortunate enough to have the right genetics.


Commercial pet foods are manufactured using high-heat processes.7

Heat processing makes pet food more allergenic7,8 and carcinogenic9. It also disrupts the structure of proteins, resulting in the loss of amino acids (such as taurine) from the original ingredients.6

When heated, proteins in the food interact with sugars and undergo non-enzymatic glycosylation – this is known as the Maillard reaction.7 The reaction produces melanoidin protein complexes, which are poorly digested, and are absorbed across the gut mucosa, thus provoking an immune response.7,8

The authors of a case-controlled study in the Journal of Nutrition (1996)6 showed that the Maillard reaction reduces taurine levels. They suggested that products of the reaction alter gut microbes in such a way that promotes taurine deficiency (via increased degradation, and decreased recycling).

The Maillard reaction also leads to the formation of damaging compounds. A study in the journal, Mutation Research (2003)9 analysed 25 commercial cat and dog foods for the presence of mutagenic compounds such as carcinogens and heterocyclic amines.

Twenty-four of the foods tested positive, and the authors hypothesised that there is a connection between the consumption of the compounds via commercial pet food, and the high rates of cancer in domestic dogs and cats.


Adverse Food Reactions (AFR) in dogs are routinely diagnosed by putting the dog on a limited antigen diet (novel protein, or hydrolysed diet) for a period of time to see if complete removal of common proteins alleviates symptoms. These food trials fail to be of use for either diagnostics or treatment if the diets are contaminated with common proteins.

Limited antigen diets have gained a significant market share in recent years. They are available at a premium cost from Vet clinics, and many other pet food retailers.

A U.S. study (2011)10 tested four over-the-counter, dry, venison dog foods to see whether they were contaminated with common allergens (soy, poultry and beef) that were not declared on the label.

All of the samples were contaminated with food allergens not declared on the label and therefore would be unsuitable for food allergy elimination diets, which is something that they would routinely be bought for.

A recent study in the Journal of Animal Physiology and Animal Nutrition (2013)11 examined 12 canine limited antigen diets from 5 different manufacturers (11 novel protein, and 1 hydrolysed) for potential contamination with proteins not listed on the label.

The authors found that 10 of the 12 foods tested were contaminated with one or more potentially allergenic proteins or fats not listed on the labels. They concluded that the use of a non-commercial novel-protein diet should be considered for ruling out AFR.

The authors discussed a previous study (Ricci et al, 2009)12 which showed that processed limited antigen diets have significantly higher amounts of omega-3 fatty acids added to them (compared to normal processed diets). They suggested that the anti-inflammatory effect of the extra omega-3 fatty acids is responsible for the transient improvement in symptoms that is sometimes seen on limited antigen diets.

Dog owners pay a premium for these diets, but there is a growing body of evidence that many (if not most) of these diets are marketed with false information.


We already know that, despite labelling requirements, the nutritional panels on processed cat and dog foods commonly fail to truthfully represent what is actually contained in the food. There is no requirement for the many chemicals present in the packaging to be listed, but there is evidence that some of these chemicals can leech into the food. They are then ingested and metabolised by the cat or dog, and may cause health problems.

BPA (an industrial chemical used to make plastics and resins) is an endocrine disruptor with oestrogenic activity, thus it can increase the rate of proliferation of some cancer cells. BPA easily passes across the placenta. It is commonly used to coat metal surfaces that will be holding food.

At least 25 different types of lacquers (such as BPA epoxy resins and polyvinyl chloride organosols) line food-grade cans. These compounds can migrate into the food. The processes used to prepare tinned pet food are known to cause leeching of BPA into the food. Smaller cans may pose a higher risk – the surface area on food in contact with the interior surface of the can is greater in smaller cans.

A study from Miyazaki University in Japan (2002)13 tested 15 tinned cat foods and 11 tinned dog foods for BPA. They also measured the amount of BPA leeching into the food.

BPA was found to be present, and leeching at varying levels in all the samples.

Note: BPA replacements in ‘BPA-free’ plastic and metal food products are now known to have similar endocrine disrupting characteristics.

A study in the Journal of the American Veterinary Association (2004)14 confirmed what previous studies had shown: a significant association between hyperthyroidism in cats (especially females) and a history of eating tinned food (especially the ‘pop top’ tins which do not require a tin opener).

Heavy metals (such as mercury) and BPA contaminate commercial processed cat and dog food. BPA inhibits thyroid function. The body attempts to eliminate BPA via a process called glucuronidation. Glucuronidation is slower in cats than other species.

The authors conclude:

“we suggest that cat owners limit the feeding of foods packaged in pop-top cans when possible. If owners follow these recommendations, however, a reduction in the incidence of hyperthyroidism in cats may not be seen for many years because cats presently consuming foods in pop-top cans may have already developed irreversible thyroid damage.” 14


Processed food is convenient and relatively cheap (unless you factor in potential lifetime healthcare costs). AAFCO-approved foods have achieved a gold-standard status of nutritional safety and completeness - however there is ample scientific evidence to show that this status is unmerited.

A minimally processed, high quality, well-planned, species-appropriate diet - one that closely resembles the natural diet of the wild counterparts of domestic carnivores - is logically the best way to avoid the pitfalls of processing, and the guesswork that goes into developing nutritional guidelines.

Update: This May 2017 article in the Veterinary Times adds further to the evidence that processed pet foods are commonly not meeting their own labelling claims.


* Joanna Blythman, Swallow This: Serving Up the Food Industry’s Darkest Secrets. Published by Fourth Estate, London, 2015

1. EC Gosper, D Raubenheimer, GE Machovsky-Capuska, and AV Chavesa, Discrepancy between the composition of some commercial cat foods and their package labelling and suitability for meeting nutritional requirements. Australian Veterinary Journal (2016), 94(1-2)

2. S. M. Hodgkinson, B. Sc., M. Sc., Ph. D., C. E. Rosales, Ing. Agrón, D. Alomar, Ing. Agrón., Mg. Sci., D. Boroschek, M.V., Chemical nutritional evaluation of dry foods commercially available in Chile for adult dogs at maintenance. Arch. med. vet. (2004) 36(2),

3. Hendriks, WH; Tarttelin, MF, Nutrient composition of moist cat foods sold in New Zealand. Proceedings of the Nutrition Society of New Zealand (1997), 22:202-207

4. Jessica E. Markovich, DVM; Lisa M. Freeman, DVM, phd; Cailin R. Heinze, VMD, MS, Analysis of thiamine concentrations in commercial canned foods formulated for cats. JAVMA (2014), 244:2

5. Robert C. Backus, DVM, PhD; Gabrielle Cohen, DVM; Paul D. Pion, DVM, DACVIM; Kathryn L. Good, DVM, DACVO; Quinton R. Rogers, PhD, DACVN; Andrea J. Fascetti, VMD, PhD, DACVN, DACVIM, Taurine deficiency in Newfoundlands fed commercially available complete and balanced diets. JAVMA (2003), 223(8)

6. Seungwook w. Kim, Quinton r. Rogers and James g. Morris, Maillard Reaction Products in Purified Diets Induce Taurine Depletion in Cats Which Is Reversed by Antibiotics. The Journal of Nutrition, (1996), 126:195-201

7. Manon de Wit, Immunological response to dietary proteins in cats. Veterinary Medicine, Research Project at Massey University, Palmerston North. Supervisors: Massey University, New Zealand Nick Cave, BVSc. MVSc. PhD. MANZCVS. DipAC. Utrecht University, The Netherlands Esther Hagen-Plantinga, PhD. DVM. MSc. August 2013

8. Nick Cave BVSc, MVSc, MSCVSc, Home prepared diets. DACVN Institute of Veterinary, Animal, and Biomedical Sciences Massey University, Palmerston North, New Zealand,

9. Mark G. Knize, Cynthia P. Salmon, James S. Felton, Mutagenic activity and heterocyclic amine carcinogens in commercial pet foods. Mutation Research 539 (2003), 195–201

10. D. M. Raditic, R. L. Remillard and K. C. Tater, ELISA testing for common food antigens in four dry dog foods used in dietary elimination trials. Journal of Animal Physiology and Animal Nutrition 95 (2011), 90–97, DOI: 10.1111/j.1439-0396.2010.01016.x

11. R. Ricci, A. Granato, M. Vascellari, M. Boscarato, C. Palagiano, I. Andrighetto, M. Diez & F. Mutinelli, Identification of undeclared sources of animal origin in canine dry foods used in dietary elimination trials. Journal of Animal Physiology and Animal Nutrition 97 (2013) 32–38, DOI: 10.1111

12. Ricci, R.; Berlanda, M.; Tenti, S.; Bailoni, L., Study of the chemical and nutritional characteristics of commercial dog foods used as elimination diet for the diagnosis of canine food allergy. Italian Journal of Animal Science (2009) 8, 328–330.

13. Jeong-hun Kang, Fusao Kondo, Determination of bisphenol A in canned pet foods. Research in Veterinary Science (2002) 73, 177–182, doi:10.1016/S0034-5288(02)00102-9

14. Charlotte H. Edinboro, DVM, PhD; J. Catharine Scott-Moncrieff, VetMB, MS, DACVIM; Evan Janovitz, DVM, PhD, DACVP; H. Leon Thacker, DVM, PhD, DACVP; Larry T. Glickman, VMD, DrPH, Epidemiologic study of relationships between consumption of commercial canned food and risk of hyperthyroidism in cats. JAVMA (2004), 224 (6)


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