GM Free Cymru

Pet foods with genetically modified ingredients put dogs & cats at risk

By Dr. Michael W. Fox*

Two widely used ingredients in many manufactured dog and cat foods contain corn and soy. These ingredients have no place in cat food because cats are strict ‘obligate’ carnivores. Corn can cause cystitis---bladder inflammation—in cats, and soy causes gas and indigestion in many dogs and cats, possibly also contributing to usually fatal bloat in dogs. The high cereal content in pet foods contributes to dogs and cats developing stones or calculi in their lower urinary tracts, often resulting in blockage requiring emergency surgery because the animals cannot urinate.

These diet-related problems have been known for decades, but it was not until the mid 1990s that I began to suspect diet may play a role in a “cluster” (see below) of health problems not seen as nearly as often when dogs and cats were being fed conventional corn and soy. Yet they usually got better when corn and soy were removed from their diets. It was in the mid- 1990s that more and more genetically engineered corn and soy were being used in pet foods and fed to farmed animals and I began to receive more and more letters from cat and dog owners whose animals were suffering from this cluster of health problems.

I do not run a private veterinary practice but work as a veterinary consultant and author of the nationally syndicated newspaper column “Animal Doctor” which I have been doing for over 40 years. This has given me a wide-angled and historical perspective that I would never have realized running a conventional veterinary clinic, the thousands of letters that I receive from across the U.S. keeping me informed about new and emerging health problems and veterinarians’ responses to same. People often wrote to me when veterinary treatments for this cluster of ailments failed, often with harmful side-effects from prescribed remedies, especially with steroids, and problems with various manufactured prescription diets.

As I began to connect the dots linking this cluster of health problems with what the animals were eating, and before I had the evidence based medicine of recovery following removal of genetically modified (GM) corn and soy from their diets, I considered other possible factors. Causes or co-factors which might contribute to this cluster of common companion animal illnesses include: adverse vaccine reactions (vaccinosis); genetic factors, especially in pure breeds and their hybrids; agrichemical and food animal drug residues contaminating pet food ingredients. In my assessment, while any of these co-factors might be involved, there had not been any significant change in this ‘background’ because there had been no significant changes to my knowledge in vaccination protocols, animals’ genetic background or in the commonly used agrichemicals and farmed animal drugs.

These animals were suffering from what attending veterinarians were diagnosing and treating as allergies, asthma, atopic dermatitis and other skin problems, irritable bowel syndrome, inflammatory bowel disease, colitis, recurrent diarrhea, vomiting, indigestion, along with abnormalities in liver, pancreatic and immune system functions.

It is surely no coincidence that the US Centers for Disease Control and Prevention reported, in Oct. 2008, an 18% increase in allergies in children under the age of 18 years, between 1997-2007. Some 3 million children now suffer from food/ digestive allergies or intolerance, their symptoms including vomiting, skin rashes, and breathing problems. They take longer to outgrow milk and egg allergies, and show a doubling of adverse reactions to peanuts. Dogs and cats, like the proverbial canaries down the mine shafts, have become our sentinels alerting us to health hazards in the home-environments we share and in the products and by-products of the same agribusiness food industry which feeds most of us and them. In my professional opinion there is sufficient proof from evidence based medicine that dietary ingredients derived from GM crops are not safe for companion animals, and by extension, for human consumers either.

I am not saying that every animal with the above ‘cluster’ of health problems got better after GM ingredients were no longer fed to them, because it is quite possible that simply improving their diets by providing better quality ingredients made the difference for some. But when we look at the feeding trials under controlled laboratory conditions in test animals given GM foods, it is indeed striking that very similar adverse effects were reported in these test animals as were found in companion animals fed GM-containing pet foods.

Scientific Research Validation

In the creation of GM crops like corn and soy bean, novel proteins are created that can cause allergies and assault the immune system creating illness, especially to the offspring of mothers fed such foods, and to their young fed diets containing GM ingredients. The genetic modification of such food crops can also alter their nutrient content, lowering phytonutrients, may elevate potential toxins, and also create novel RNA variations. The latter are not destroyed by digestion and so called micro RNA has been found in mammalian tissues where they can exert influences on gene expression and therefore affect health across generations, ( Zhang et al, 2011). These kinds of problems are in part due to the inherent genetic instability of GM plants that can result in spontaneous and unpredictable mutations, (Wilson et al 2006).

Controlled laboratory animal studies, like those summarized by Pusztai et al (2003), Domingo (2007) Smith (2007) and Fox (2011), are too often dismissed as not being relevant to real-life conditions, and if there were adverse health consequences, they would be readily diagnosed since GM crops and foods are now being grown and consumed globally. But a simple diagnosis pinpointing GM factors is not easily made because of all the many variables in food constituents and environmental and other disease co-factors.

One of the biggest challenges today in addressing human and animal health and various complex disease problems is in the accurate identification of causal factors responsible for illness. This is essential if effective government regulation, oversight and preventive measures are to be implemented, and where feasible, appropriate treatments.

Possible causal factors in some of the health problems commonly occurring in companion animals include thousands of chemicals and synthetic organic compounds derived from various industrial and agricultural sources and which variously enter the environment, and what is eaten, drunk and inhaled.

Recent toxicological advances have identified certain effects of these substances on the body, such as endocrine (hormonal) and metabolic (obesogenic and diabetogenic) disruption, as well as causing cancer, mutations and birth defects, notably herbicides like glyphosate, the main ingredient in Monsanto’s Roundup herbicide, compounds like the phthalates and Bisphenol A in plastics and food containers, the omnipresent flame-retardant bromide compounds (PBDEs), and dioxins and PCBs.(For a review visit my website

Now when it comes to making a risk assessment of genetically modified (GM)/ genetically engineered food ingredients, primarily derived from herbicide resistant crops (and therefore containing herbicide residues as well as endogenously produced insecticide like Bt), supporters of such biotechnology are quick to point out that because so many chemical compounds already contaminate our environment, bodies and food, you just can’t prove that GM crops and food are harmful.

However, in their detailed review of animal safety studies of GM foods, Dona & Arvanitoyannis (2009) conclude that “The results of most of the rather few studies conducted with GM foods indicate that they may cause hepatic, pancreatic, renal, and reproductive effects and may alter hematological, biochemical, and immunologic parameters the significance of which remains unknown. The above results indicate that many GM foods have some common toxic effects. Therefore, further studies should be conducted in order to elucidate the mechanism dominating this action. Small amounts of ingested DNA may not be broken down under digestive processes and there is a possibility that this DNA may either enter the bloodstream or be excreted, especially in individuals with abnormal digestion as a result of chronic gastrointestinal disease or with immunodeficiency.”

In a study analyzing the effects of genetically modified foods on mammalian health, researchers found that three varieties of Monsanto's GM corn - Mon 863, insecticide-producing Mon 810, and Roundup® herbicide-absorbing NK 603, approved for consumption by US, European and several other national food safety authorities, caused liver, kidney and other internal organ damage when fed to rats. Researchers Vendomois and co-workers (2009) summarized these findings as follows:

"Effects were mostly concentrated in kidney and liver function, the two major diet detoxification organs, but in detail differed with each GM type. In addition, some effects on heart, adrenal, spleen and blood cells were also frequently noted. As there normally exists sex differences in liver and kidney metabolism, the highly statistically significant disturbances in the function of these organs, seen between male and female rats, cannot be dismissed as biologically insignificant as has been proposed by others. We therefore conclude that our data strongly suggests that these GM maize varieties induce a state of hepatorenal toxicity....These substances have never before been an integral part of the human or animal diet and therefore their health consequences for those who consume them, especially over long time periods are currently unknown."

The insecticidal toxin Bt (from the inserted genes of Bacillus thuringiensis) in many varieties of GM corn may create allergies and illness, and which, like other inclusions in GM food crops, especially novel proteins, has not been adequately tested for consumer safety and potential health risks, especially prenatally, epigenetically and across generations. Altered DNA from GM foods can be incorporated by gut bacteria and may alter their behavior and ecology in the digestive tract. Likewise the bacterial incorporation of genetic material from antibiotic resistance genes used to identify some varieties of GM food crops could have serious health implications, (see Smith 2007 and Traavik & Heinemann, 2007).

Many of the pathological, physiological, anatomical and developmental changes documented in laboratory animals fed GM foods may be eventually identified by veterinary pathologists and immunologists doing detailed forensic and toxicological studies of diseased, dying and dead companion animals. But currently such research, to the best of my knowledge, is neither being conducted nor funded. So I advise both consumers and pet care-givers to avoid all foods derived from GM crops because the findings of evidence-based medicine support the growing consensus that such foods are unsafe and not fit for man or beast.

The discovery that food ingredients can influence gene expression, causing their activation or suppression, has opened up a new field of research called nutrigenomics. The protective effects of certain foods and diets against various cancers are associated with such activation and suppression processes. In a second generation of chickens fed organically grown feed compared with those fed the same diet but of conventionally grown ingredients, the organically fed birds had more activated genes responsible for cholesterol regulation and immunological processes, ( Greef et al 2009).

In sum, animals are changed by what they eat, and this discovery raises serious questions when it comes to feeding animals (and our selves) genetically engineered foods containing novel proteins and DNA. Prof. Jack A. Heinemann (2009) states:”There is substantial literature that reports the detection of DNA and protein unique to GM plants within animals and animal products. Based on studies, it is not possible to conclude that animals and derived products are free of GM material when they have been exposed to GM plants through i) feeding, ii) proximity to other animals on GM feed, or iii) subsequent processing. The most consistent finding in the literature is that---- there is compelling evidence that animals provided with feed containing GM ingredients can react in a way that is unique to an exposure to GM plants. This is revealed through metabolic, physiological or immunological responses in exposed animals. In the absence of appropriate testing, we can't assume that raising an animal on GM feed will not affect the final product – even if there is no detectable residue from the GM material”.

Environmental changes can trigger harmless micro-organisms to mutate, proliferate and even evolve into more harmful varieties (pathogens). Environmental changes associated with the planting of herbicide resistant, genetically modified (GM) corn, soybean, sugar beet, and alfalfa and with the repeated applications of the herbicide glyphosate (Monsanto’s Roundup) affecting soil microorganisms, crop nutrient uptake and disease resistance, may have created a new pathogen. According to Dr. Don Huber, Professor Emeritus, Purdue University, this harmful organism, hitherto unknown to science, found in abundance in GM soybean meal, and corn products, is linked to infertility, abortions and other health problems in a wide variety of livestock, and causes Sudden Death Syndrome in soy and Goss’ wilt in corn. For details see posting on my website, and interview with Dr Huber in Acres USA magazine, May 2011.


Industrial agriculture creates consumer and companion animal health risks. More than one major pet food recall occurs every year because of the ways in which farmed animals are raised and processed, resulting in Salmonella, E.coli and other bacterial contamination, and because of how GM crops are grown and processed, leading to aflatoxin contamination and other toxic molds associated with Roundup and other herbicide applications on these crops.

There are GM corn and soy-free, and organically certified pet foods now available on the market, and websites providing recipes for home-prepared diets for companion animals ( , and which many informed cat and dog care givers are now providing for their animals. This enlightened consumer action is an integral part of the long overdue revolution in agriculture to promote more ecologically sound, sustainable and humane farming practices, a healthier environment, and more healthful, wholesome and affordable food for all.

Pet food manufacturers that have USDA Certified Organic ingredients, and especially those that use no corn, soy, canola, cotton by-products (oil & cake) or sugar beet, --- which can be GM, or GM contaminated by adjacent fields of GM crops and from cross-contamination during processing--- or imported rice (which can be contaminated with GM rice) could legitimately claim “No GM Ingredients” on their packaging.

I feel very strongly that this is a pivotal issue in the health/ food revolution, where there is no place for GM food ingredients in what we consume and feed to companion, and also to farmed -food animals. I have communicated these concerns to several responsible pet food manufacturers who are not unaware of what Hippocrates advised, --- to let our food be our medicine and our medicine our food.

For further reading see:

Fox, M.W. Healing Animals and the Vision of One Health. Tallevast, FL One Health Vision Press/ 2011 Fox, M.W., Hodgkins E., and Smart M. Not Fit for a Dog: The Truth About Manufactured Dog and Cat Food Sanger CA Quill Driver Books 2009. Smith, J.M. Genetic Roulette: The Documented Health Risks of Genetically Engineered Foods Fairfield. Iowa Yes! Books 2007. Supportive References de Greef, A. et al. Effects of organically and conventionally produced diets on jejunal gene expression in chickens. Brit. J. Nutrition 103:696-702 2009 de Vendômois JS, Roullier F, Cellier D, Séralini GE. A Comparison of the Effects of Three GM Corn Varieties on Mammalian Health. Int J Biol Sci 5:706-726, 2009 Dona A. and Arvanitoyannis,I.S., Health Risks of Genetically Modified Foods. Critical Reviews in Food Science and Nutrition. 49: 164-175, 2009 Domingo, J. L. Toxicity Studies of Genetically Modified Plants: A Review of the Published Literature. Critical Reviews in Food Science and Nutrition, 47:8, 721 – 733, 2007 Fox, M.W. Healing Animals and the Vision of One Health. Tallevast, FL One Health Vision Press/ 2011 Heinemann, J. A. Report on animals exposed to GM ingredients in animal feed Prepared for the Commerce Commission of New Zealand 24 July 2009 (Prof Heinemann's study is available here: Or via the Commerce Commission web site, at the bottom of the following page:

Pusztai A., Bardocz, S., and Ewen, S. W. B.. Genetically Modified Foods: Potential Human Health Effects. In: Food Safety: Contaminants and Toxins (ed) D’Mello JPF CAB International, Wallingford Oxon, UK, pp 347–372, 2003 Seralino G-E., et al Genetically modified crops safety assessments: present limits and possible improvements. Environmental Sciences Europe 23:10-19, 2011 Smith, J.M. Genetic Roulette: The Documented Health Risks of Genetically Engineered Foods Fairfield. Iowa Yes! Books 2007. Traavik T and J. Heinemann, Genetic Engineering and Omitted Health Research: Still No Answers to Ageing Questions, TWN Biotechnology & Biosafety Series 7, 2007 Wilson A.K, J.R.Latham, and R.A.Steinbrecher, ‘Transformation-induced mutations in transgenic plants: Analysis and biosafety implications. Biotechnology and Genetic Engineering Reviews, 23: 209-226, 2006. Zhang, L. et. al., Exogenous plant MIR168a specifically targets mammalian LDLRAP1: evidence of cross-kingdom regulation by microRNA. Cell Research, doi:10.1038/cr.2011.158, 2011

ADDENDUM The capacity of GMOs to cause harm---dysbiosis, allergies and immune system dysfunction---may well be enhanced by animals being raised in relatively sterile home environments and fed heat-processed foods so that they do not acquire a healthy and diverse population of intestinal bacteria. Antibiotic residues in their foods, and the widespread use of such drugs to treat various skin, ear and other often diet-related health problems, ( many of which could have been prevented with a more wholesome diet and probiotics), are additional factors to consider in adopting a more holistic and integrated approach to both animal and human health and disease prevention. To be more specific, bacteria obtained from the environment play a pivotal role in the development of a competent immune system, more regulatory T-lymphocytes that drive the immune response being found in the intestinal tissues of farm-reared versus isolation-reared piglets. (Veterinary Record “Immunological benefits of growing up on farms” Vol. 170: p.168, 2012 and Lewis, M.C. et al “Direct environmental evidence that early-life farm environment influences regulation of immune response”. Pediatric Allergy and Immunology doi: 10.1111/j.1399-3038. 2011.01258.x)).These observations are supported by other research showing that mice treated with a broad range of oral antibiotics to diminish or deplete their intestinal bacteria had elevated levels of antibodies known to be important in allergies and asthma (IgE class antibodies). The elevated antibodies in turn increased the levels of basophils, immune cells that play a role in inflammation, both allergic and otherwise. Commensal intestinal bacteria apparently limit this proliferative capacity. (See Hill, al “Commensal bacteria–derived signals regulate basophil hematopoiesis and allergic inflammation” Nature Medicine (2012) doi:10.1038/nm.2657 Published online 25 March 2012).

These findings apply to humans and other animals who have high levels of IgE for genetic and other reasons. One reason could be some of the components in their food from GMOs. Those with elevated levels of IgE are highly susceptible to eczma and infections, antibodies that neutralize IgE being now used to treat asthma.

Another study on mice has shown that bacteria in early life may inhibit the production of NKT cells (natural killer cells that detect antigens [prevalent in novel-protein-containing GMO containing foods] in the lungs and colon that produce large amounts of inflammatory cytokines). This is done by the bacteria blocking a stimulator skin protein called CXCL16, high levels of which are associated with autoimmune diseases such as ulcerative colitis, an inflammatory bowel disease, and asthma. (See Torsten Olszak et al “Microbial Exposure During Early Life Has Persistent Effects on Natural Killer T Cell Function”. Science DOI: 10.1126/science.1219328 Published Online March 22 2012).

A wholly different correlation with the onset of health problems assocated with the increasing inclusion of GMOs in pet foods comes from the entomological research on Monarch butterflies. A dramatic decline of 81% in numbers of this migratory species between 1999 and 2010 associated with the planting of ever more acres of Roundup-ready corn and soybean and the use of Roundup (glyphosate) herbicide (currently used by 94 % of soybean and 72 % of corn producers), eliminating the insects’ milkweed life-source was reported by K. Oberhauser & J. Pleasants (Insect Conservation & Diveristy, on line publ. March 2012). The presence of this herbicide in GM soy and corn may kill gut bacteria, and GMO transgenes may transfer to gut flora altering function to the detriment of consumers, human and animal.

NOTE: The US Food and Drug Administration (FDA) does not require GMO testing. Genetically engineered foods are in 80% of packaged human foods and many beverages. Genetically engineered foods, derived from GMOs, have never been proven safe for human consumption but have been on the market for the last two decades. For a list of hidden GMO ingredients and tips for avoiding GMOs, go to

The pseudo-scientific term “substantial equivalence” has been coined by the biotechnology food industry to assuage regulators and concerned consumers over the lack of scientific safety tests prior to government approval of GMOs which are by their very nature in no way substantially similar to conventional crops and foods. To claim any such equivalence is biologically absurd science fiction.


To confront GMO issue as I see it strikes at the very core of the mammonist world view and ethical black hole that rationalizes the expropriation and patenting of fundamental life processes for short term profit under the guise of ‘progress’ but in total disregard for the sanctity of life, potential risks and long term irreversible consequences. As I have written earlier, it may well boomerang and pave the way for a rapid transition to sustainable, humane, socially just organic food production systems. The recovery of agri-culture and corporate sanity go hand in hand!

*Consultant veterinarian and syndicated newspaper columnist. Web site