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Genetically Modified Food Ingredients (GMOs) Put Dogs, Cats, and Other Consumers at Risk

“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.” ~ Dr. Michael W. Fox

Dr. Fox writes the nationally syndicated newspaper column Animal Doctor featured in the Washington Post.  He is a member of the British Veterinary Association, the American Holistic Veterinary Medical Association, Founding Member of the International Society for Applied Animal Ethology, and an Honor Roll member of the American Veterinary Medical Association.

This article by Dr. Fox delves into the “cluster” of health problems reported by veterinarians, including allergies, asthma, atopic dermatitis and other skin problems, irritable bowel syndrome leaky gut syndrome, inflammatory bowel disease, colitis, recurrent diarrhea, vomiting, indigestion, along with abnormalities in liver, pancreatic and immune system functions.

By Dr. Michael W. Fox

Our canine and feline animal companions are like canaries down in the mines, alerting us to possible dangers in the environments we share. Since they consume some of the same dietary ingredients from the same food chain that we share with them, the following concerns about genetically modified (GMO) food ingredients that seem to be contributing to a variety of veterinary medical conditions, —and which improve when GMOs are excluded from their diets—should also alert us all as consumers of such genetically altered, biologically anomalous foods.

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, even epilepsy in dogs 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.

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

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.

In the absence of costly feeding trials of pet foods on dogs and cats, there can be no absolute certainty that GMO food ingredients alone are responsible for these health problems. But to claim that GMOs (of which there is no real need in agriculture) are harmless is to disregard the precautionary principle. This must be applied in the light of controlled feeding trials in laboratory animals who developed a multitude of  health problems and organ damage associated with GMOs in their diets. From the perspective of the precautionary principle no GMOs should be included in pet foods..

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 farmed animal drugs or in agrichemicals with two exceptions, the herbicide glyphosate (Monsanto’s Roundup) and the insecticidal toxin Bt..

As I document below, what is particularly significant is the discovery that genetic material (RNA) in the foods we eat and give to our animals can affect critical gene functions at the cellular level ( including that of embryos) because they are absorbed into the body and are not destroyed by digestive processes. Biologically novel RNA from GMOs, never present heretofore in the food chain, as well as anomalous phytochemicals and agrichemical residues in genetically engineered crops, could be harbingers of a host of diet-related or aggravated health problems in consumers, human and non-human, especially in those with genetically associated susceptibilities, yet to be identified.

  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. This ties in with the time-frame of when GMOs were first introduced into the food chain and then subsequently in greater amounts. 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.

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.

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).

Bt-toxin from genetically engineered corn sources has been found in the blood of pregnant women and their babies, as well as in non-pregnant women. (Specifically, the toxin was identified in 93% of 30 pregnant women, 80% of umbilical blood in their babies, and 67% of 39 non-pregnant women.)

 Bt-toxins, which have been shown to damage human kidney cells, may cause leaky gut syndrome in newborns, the passage of undigested foods and toxins into the blood from the intestines leading to food allergies and autoimmune diseases. Also, since the blood-brain barrier is not developed in newborns, toxins may enter the brain causing serious cognitive problems. Some healthcare practitioners and scientists are convinced that this is the apparent mechanism for autism

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 ourselves) 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.

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