Dogs and cats, like the proverbial canaries down the mine shafts, have become our sentinels. They alert us to health hazards in the home-environments we share and in the products and by-products of the same agribusiness food industry that feeds most of us and them. In the mid 1990s I began to suspect diet may play a role in a “cluster” of health problems not seen nearly as often as when dogs and cats were being fed conventional corn and soy. Since that time I have formed the professional opinion that 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. Widespread use of GMO crops In the mid 90s, more and more genetically engineered corn and soy were being used in pet foods and fed to farmed animals.

As a nationally syndicated veterinary newspaper columnist, I began to receive an increase in letters from cat and dog owners whose animals were suffering from this cluster of health problems. In the 40 years that I’ve been writing that column, I’ve benefited from 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. keep me informed about new and emerging health problems and veterinarians’ responses to the same. During this timeframe in the 90s, people often wrote to report of failed treatments and harmful side effects to prescribed remedies e.g. steroids, as well as problems with various manufactured prescription diets after their attending veterinarians diagnosed their animals with 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.

That animals with these afflictions often recovered completely when I advised that they be taken off all foods containing corn and soy supported the evidence based medical assertion that dietary ingredients were playing a significant, if not sole role in their disease.

A similar picture was developing in human health. 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 GM ingredients were first introduced into the food chain and then subsequently in greater amounts. Some 3 million children now suffer from food and/or 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.

Research Evidence of Harms

In the creation of GM crops like corn and soy bean, novel proteins are created that can cause allergies and assault the immune system. This in turn creates illness, especially in 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 lower their nutrient content, 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).

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.” 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).

Three varieties of Monsanto’s GM corn, 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, ( Vendomois et al 2009). A subsequent 2-year feeding trial by Seralini et al (2012) reported that rats fed on a diet containing NK603 Roundup tolerant GM corn or given water containing Roundup, at levels permitted in drinking water and GM crops in the US, developed cancers faster and died earlier than rats fed on a standard diet. Females developed significant and numerous mammary tumors, pituitary and kidney problems. Males died mostly from severe liver and kidney chronic deficiencies.

The insecticide Bt (from the inserted genes of Bacillus thuringiensis) produced by several varieties of GM corn may create allergies and illness. 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. 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 and cause serious cognitive problems. Some health care practitioners and scientists are convinced that this is the apparent mechanism for autism.

Where does that leave us? Genetically engineered foods, derived from GM crops, have never been proven safe for human consumption but have been on the market for the last two decades. You can find a list of hidden GMO ingredients, as well as tips for avoiding GMOs, visit

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 could be genetically engineered, or imported rice (which can be contaminated with GM rice) could legitimately claim “No GMO 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.

* The author is an Honor Roll Member of the American Veterinary Medical Association, website His most recent books are Healing Animals & the Vision of One Health, and Animals & Nature First. He is co-author of Not Fit for a Dog: The Truth About Manufactured cat & Dog Food.

For further reading see: Fox, M.W. Healing Animals and the Vision of One Health. Tallevast, FL One Health Vision Press/ 2011 and 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 2012. Smith, J.M. Genetic Roulette: The Documented Health Risks of Genetically Engineered Foods Fairfield. Iowa Yes! Books 2007.

For Supportive References: See detailed review on this topic at