1. The theoretical arguments presented to support feeding raw diets to dogs and cats are mostly nonsense.
a. Raw diets are “natural”
b. Dogs and cats can’t digest grains
c. Raw diets contain needed enzymes or “life energy”
d. Commercial diets are full of “toxins” or otherwise unhealthy
2. There is no evidence to show a benefit to feeding raw diets apart from individual anecdotes and testimonials, which are not reliable.
3. There is limited evidence of potential harm from raw diets, including infectious diseases, parasitism, trauma from bones, and nutritional deficiencies.
A new review of the literature concerning raw diets of animal companions appeared in January in the Canadian Veterinary Journal, and it confirms these concluions.
Schlesinger, DP. Joffe, DJ. Raw diets in companion animals: A critical review. Canadian Veterinary Journal 2011;52-54.
The authors begin by reviewing some of the reasons people are interested in feeding such diets. These include concerns about the safety or nutritional adequacy of commercial diets and a desire to feed our pets in ways we perceive as healthful, just as we wish to feed ourselves and our children. These are, of course, legitimate motives. But they don’t make the mythology behind raw diets any less false nor remedy the lack of evidence for safety or benefit. The fact remains that the best, most effective choices in the care of our pets are those we make based on sound scientific evidence.
In this article, the evidence concerning raw diets is evaluated according to a scale of quality which is described in the article and which is commonly used to evaluate research evidence. In this scale, Level 1 evidence would consist of multiple high quality studies which agree or which have unequivocal results. No Level 1 quality evidence was identified for either potential risks nor benefits to raw diets.
Levels 2 and 3 evidence would be data from fewer or slightly lower quality population studies. Level 4 evidence would be from poor quality group studies or simply collections of uncontrolled case reports. And Level 5 evidence is essentially just opinion or extrapolation from basic theoretical principles.
The authors found no Level 2 or 3 evidence for a benefit from raw diets. The only published study at all cited concerning raw diets and health was a survey of owners in Australia which reported that over 98% of owners thought their pets were healthy, and between 10-16% of the pets these individuals owned ate some raw food. Clearly this says absolutely nothing about the relationship between health and feeding of raw diets, and it is quite a stretch to even view it as relevant to the question.
The authors found a Level 5 paper which reviewed the literature in humans concerning the question of whether enzymes in raw foods increased the nutritional quality of this food for humans. This paper concluded that there is no evidence of harm from the absence of such enzymes in cooked food and not enough information available to identify if the presence of such enzymes has any real significance.
Another Level 5 article was discussed which looked at the effect of raw foods (not meat) on cardiovascular disease risk in humans and concluded that some risks might decrease and others increase with such a diet. Obviously, there is no reliable, meaningful information in either of these articles to support benefits from raw diets fed to dogs and cats.
No Level 2-3 evidence was identified concerning nutritional risks from feeding raw diets. Several case reports were found (Level 4 evidence) of pets who suffered from nutritional deficiencies or excesses from being fed raw diets, and a survey of 5 raw diets, both commercial and homemade, identified such deficiencies or excesses in all of the diets.
Level 2, 3, and 4 evidence was found to support that raw diets present a significant risk of infectious disease for pets fed these diets and their owners. Many raw diets, both commercial and homemade, test positive for E. coli and Salmonella, potentially deadly food-borne bacteria. Both dogs and cats fed such diets have been shown to shed these organisms in their feces. Both pets and humans in contact them have developed active infections with these bacteria and some have become ill as a result. Freezing and standard cleaning and disinfecting practices do not effectively control this risk, and some of the organisms identified in these diets were resistant to typical antibiotics used to treat people infected with them.
So the conclusions I came to two years ago have not changed. There is no top quality evidence concerning the potential risks and benefits of feeding raw diets to dogs and cats. There is no evidence of any level other than mere opinion and anecdote to support claims that these diets are beneficial. There is, however, reliable evidence for real and significant risks associated with these diets. At this point in time, then, the balance of the evidence does not support feeding raw diets. Until and if a benefit can be shown by objective, scientific research, that outweighs the known risks, such diets should be avoided.