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Debating raw diets

Surveys show that pet owners who feed raw diets are less likely to trust nutrition advice from veterinarians

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Despite resistance from most veterinarians and from public health authorities, the popularity of raw meat-based diets for dogs and cats continues to grow.1,2 Raw feeders have a range of ideas about nutrition, but they typically believe raw diets are healthier and more ‘natural’ than cooked diets, and they often suspect conventional commercial diets are unsafe or a cause of disease.3,4

Unfortunately, it is not only pet owners who hold such beliefs. Though they are a minority, some veterinarians promote raw feeding and attack the safety and nutritional value of cooked commercial diets.5,6

Surveys show that pet owners who feed raw diets are less likely to trust nutrition advice from veterinarians and also are less likely to adhere to other recommendations (e.g. vaccination and parasite prevention) than owners who feed traditional commercial diets.3,1 Veterinarians who promote raw feeding and condemn conventional diets are also often suspicious of vaccines and other science-based medical therapies, and frequently advocate alternative medical practices.5,7,8

Though individual beliefs vary, there is a general trend for raw diets to be appealing to pet owners or veterinarians who believe more ‘natural’ diets and medical approaches are safer and better than conventional medical and nutritional practices. These beliefs are predicated on questionable concepts and are not supported by convincing research evidence.

Arguments for raw diets

The most common rationale for feeding raw is that this is a more natural diet to which dogs and cats have been adapted by evolution and which should, therefore, be healthier for them. Taxonomically, dogs and cats are carnivores (though dogs are functionally omnivores) and their ancestors ate live prey and carrion, so they must be designed for a diet as close as possible to that of wild carnivores. Some raw-diet advocates extend this argument by claiming that anatomic and physiological similarities between domestic dogs and wolves imply dogs should be fed the same diet wolves eat in the wild and domestic cats should ideally eat whole prey as wild felines do.5

Raw diets are also claimed to have specific health effects, ranging from better coat and stool quality to a lower risk of diabetes, allergies, cancer, and other serious diseases.8,9 Proponents of raw diets consistently argue that any risks are outweighed by these benefits.

The other major argument for feeding raw diets is that cooked commercial diets are nutritionally inadequate and unhealthy. Proponents of raw diets express concerns about the loss of nutrients in heating and processing, the dangerous health effects of grains and carbohydrates in commercial diets, and numerous purported toxins, ranging from by-products of processing to preservatives and other additives in canned and dry diets. Many chronic health problems are blamed on commercial pet food by raw-diet advocates.5,6,8

The evidence

The idea raw diets should be beneficial because they are ‘natural’ is simply an expression of the ‘appeal to nature fallacy,’ the misconception that anything found in nature is inherently healthier than anything produced by humans. Illustrations of why this is false are easy to find. Consider, for example, that dysentery, smallpox, and rattlesnake venom are perfectly natural, and antibiotics, vaccines, and anti-venin are clearly artificial, yet the latter are certainly better for health than the former.

It is also clear ‘natural’ is not a synonym for ‘healthy’ from the fact that parasitism, malnutrition, and infectious disease are rampant in wild animal populations and that life expectancy and health are nearly always superior for animals in appropriate captive environments.10 The diet of wild carnivores is simply the food they can get, not a perfect diet designed for long-term health. Experts in captive wild carnivore nutrition recommend commercial foods as a significant component of the overall diet for these species because such foods improve the safety and nutritional quality of the diet and the health of these animals.11–14

Even if a species-typical diet in the wild were optimal for the health of wild carnivores, however, it is obvious dogs, at least, have evolved far from their wild ancestors and would not necessarily have the same dietary needs. Evidence shows many genetic, anatomic, and physiologic differences between domestic dogs and wild canids that result from selective pressures associated with living with humans, and these have altered their nutritional requirements and the foods that will best support long-term health.15–19

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There is no compelling evidence for any of the specific health benefits claimed for raw diets, and there has been very little research investigating them.4,20 The few published studies of raw feeding have found various effects on physiologic and clinical parameters, but little sign of any significant health effects, so most health claims are purely anecdotal at this point.21–25

The claims about the hazards of commercial diets vary from implausible and completely unproven to legitimate, substantiated risks. Commercial diets can be a source of infectious diseases, and some cases of serious injury due to adulterants or other toxins have been seen.26,27 However, there is ample research evidence to support the nutritional value of properly formulated diets, and some evidence to support specific health benefits for some diets, such as renal and urolith dissolution diets.28–30 Millions of dogs and cats live long and healthy lives on commercial pet foods, so while they are not perfect or risk-free, there is little reason to believe they are a major risk factor for disease in most animals, and there is certainly no research evidence to support this claim.

The risks of raw diets

Unlike the benefits of raw diets, which are theoretical and unproven, the risks are well documented. Commercial raw diets that meet Association of American Feed Control Officials (AAFCO) standards are likely to be nutritionally complete, but many raw advocates feed home-prepared diets, and these diets are frequently nutritionally unbalanced and incomplete.4,31–35 The widespread use of bones in raw diets also presents a significant risk of dental fractures and gastrointestinal injury,36–40 though one study has suggested some possible benefits for dental health.41 Even wild carnivores are at risk for acute dental and gastrointestinal trauma from bones, as well as chronic tooth wear, and this can lead to the ‘natural’ outcomes of suffering or death.42–44 Pet dogs and cats are at least as susceptible to this risk as wild carnivores, and the natural outcomes are clearly unacceptable to owners.

The most significant risk of raw diets is from food-borne infectious disease. Illness and death in cats and dogs, and in their owners, have been caused by pathogens found in raw pet diets.4,45–51 Although such pathogens can contaminate cooked diets as well, the risk is significantly higher for raw foods.27 While healthy, immunocompetent adult pets may be able to resist these organisms to some extent, there is no absolute immunity in dogs and cats to food-borne illness. Young, old, immunosuppressed animals, and their human caregivers, are at even higher risk.

Bottom line

There are no proven health benefits to raw diets, and most of the claims rest on dubious theoretical grounds and exaggerated fears about conventional cooked diets. There are, however, clear risks to feeding raw meat, including nutritional deficiencies or excesses, risk of injury from bones, and risk of severe infection and death in both pets and humans. While properly formulated raw diets can be nutritionally appropriate and the risks of infectious disease can be mitigated by scrupulous food handling, the established risks of raw diets and the complete lack of compelling evidence for any health benefits make the use of such diets a choice based on ideology or personal belief, not sound scientific evidence.

References
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Brennen McKenzie, MA, M.Sc., VMD, cVMA, discovered evidence-based veterinary medicine after attending the University of Pennsylvania School of Veterinary Medicine and working as a small animal general practice veterinarian. He has served as president of the Evidence-Based Veterinary Medicine Association and reaches out to the public through his SkeptVet blog, the Science-Based Medicine blog, and more. He is certified in medical acupuncture for veterinarians. Columnists’ opinions do not necessarily reflect those of Veterinary Practice News Canada.

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