Raw Diets for Pets: Still No Evidence of Benefit but a Real Risk of Harm

I’ve written before about raw diets for pets, and at the time my conclusions were these (see the previous articles for details 1, 2):

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.

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15 Responses to Raw Diets for Pets: Still No Evidence of Benefit but a Real Risk of Harm

  1. hornblower says:

    You won’t get the studies – not for many years because the institutional & corporate bias is in the opposite direction: to provide scientific ‘proof’ of the benefits of manufactured diets.

    As a lactation consultant, we faced the same problem with breastfeeding. Until the last 10-20 years, what we had was tons of studies about artificial baby milk, aka formula. Even now, getting good large studies which are not influenced by the large corporations is tough.

    When a small group of companies benefits from maintaining their market share, it’ll always be an uphill struggle to get the large scale studies which we all want.

    Oh & yeah – I have 2 dogs on raw, 1 dog on kibble & 1 cat on canned. 🙂

  2. skeptvet says:

    I don’t agree. It is true that companies who manufacture pet food do fund much of the research into pet nutrition, and this has the potential to introduce bias. But with a growing market in commercial raw diets, the same motivation exists to generate research evidence that can be used to promote these products, so I think the market incentives could lead to industry-funded research, with all its pros and cons.

    And let’s not forget that universities, foundations, and other sources of funding for rsearch are available. I don’t think it is reasonable to simply give up and say that because the big bad corporations aren’t interested we can’t have any evidence so we should just do whatever we want. The same argument is made for herbal remedies and supplements, and yet these are industries with billions of dollars in sales and with millions more spent by the NCCAM to study their products, so I think it can too easily become an excuse for acting without evidence. If people believe in these diets, and if they wish to promote or even sell them, then they can find a way to study them if they really want to. With homemade diets, it would really be pretty inexpensive to do.

    And, of course, in the absence of the highest quality studies, how do we evaluate such practices? Proponents would argue that anecdotes and personal experience is sufficient to justify feeding raw, but that has proven so unreliable for so many therapies in the history of medicine that it isn’t defensible. Analysis of the basic science and animal model research already available on the subject can contribute to rational decision making, even if it is not as high a level of evidence as clinical trials. And in the case of raw diets, the underlying theories are contradicted by established knowledge of physiology and nutrition, so that leans against the practice.

    In practice, I tell clients exactly what the evidence says: bogus theories, no evidence of benefit, small chance of harm. I think it is possible to make a reasonable tentative conclusion based on that, and the conclusion is there is no good reason to feed these diets. I suspect if enough pet owners are interested, studies will eventually be done, and if they accumulate adequate quality, reproducible positive results over time then I would certainly encourage feeding these diets. But at this point, the balance of the evidence, weak as it is, is against the practice.

  3. Mike Mason says:

    I am all for evidence based decision making in all areas of practical life, but I am confused by some of the debate over raw diets. The kicker statement in the review you discuss is “There are no published level 1, 2, or 3 studies of nutritional risk
    or benefit of raw meat feeding to dogs or cats.” A look at their references reveals almost nothing even mentioning this main topic. Almost everything is about salmonella. Golly, dog poop has germs – who knew.

    It seem that if there is no research to speak of (why?) then the default position would be to feed your pets real food – a variety of fresh meats, grains and vegetables. Just like people are supposed to eat. You don’t need to invoke woo-y explanation about life forces etc., just some basic nutritional principles. After all, do you eat baked pellets of processed mystery mush? Why would I think it is better for pets to eat this stuff?

  4. skeptvet says:

    The problem is that your comment contains all kinds of assumptions, things you think are obviously true but may not necessarily be. I addressed a few of these in Common Pet Food Myths.

    For example, you describe raw meat and vegetables as “real food” and dog food as “mystery mush.” But the reality is that the precise nutrient composition of raw foods is variable and often unknown, and that of commercial dog food is consistent and predictable. “Common sense” mixtures of ingredients such as found in many homemade pet diet recipes turn out to be nutritionally inadequate in a lot of cases because “common sense” is a lot poorer a guide to what is nutritious and healthy than most people think. And while raw foods or organic foods are often thought to be healtier than cooked or conventionally grown foods, the evidence doesn’t actually show this to be true (e.g. 1, 2). And in my grandmother’s day, a “healthy” diet was thought to be one with lots of meat and other high fat foods, often followed by some alcohol or a smoke “to aid the digestion.” Common sense changes on a whim.

    You also suggest that what is appropriate for pets is a diet “just like people are supposed to eat.” But of course dogs, cats, and people are very differe,nt kinds of animals, and just tossing in more meat and fewer grains or something doesn’t make your idea of a healthy human diet into an optimal pet diet. There are decades of research data on what makes a healthy diet for our pets, and contrary to the mythology promoted by raw food advocates, our pets are generally very fit and healthy when fed commercial diets, so the assumption that what sounds like it ought to be a healthy diet to you is as good or better than this is just that, an unfounded assumption contrary to the facts.

    Sure, there is always the possibility that research will eventually show some kind of benefit to feeding a raw diet. But the logical position in the absence of such research is not to ignore the abundant research behind conventional pet diets and substitute your “common sense” or gut instinct about what ought ot be healthy instead.

  5. Rita says:

    “what is appropriate for pets is a diet “just like people are supposed to eat.” But of course dogs, cats, and people are very different kinds of animals,” – just so, and, of course, like any resource-using commodity, pet (i.e. supplied by owners) food has an ethical dimension, just as food “like people are supposed (by whom?) to eat” does. Those of us who think we have obligations to consider this dimension both in what we eat ourselves and in what we choose (since we have the power) to feed to our favoured companions would perhaps be more inclined to minimise the harm we do in keeping carnivorous pets at all and search for foodstuffs for them and for ourselves which are fully compatible with health (as vegan diets are for people, American Dietetic Association), whilst striving not to sacrifice the lives and well-being of other animals to the interests of our current court favourites.

  6. Dan Scott says:

    Ok here’s something novel: Lets just forget science for a moment and wonder at the hokey pokey way that raw food has helped so many dogs off precription drugs and chemically laced commercial dog food onto a new life of zero problems and wonderfull health, enery and vitality.

    My woo must be strong master for I have fixed many dogs without scientific protocol.

    Mr webmaster, go on just embrace the way, it will liberate you from your skepticism.
    To do list:
    Must not assume/
    Must not use common sense/
    Must not use gut instinct/
    Must not invoke the words natural/real/ nature or holistic.
    Stop being arrogant/
    Stop being whatever the skepvet say i’m gonna be once he jumps on me for being so downright … er… full of it!

    Raw Diets for Pets: Still No Evidence of Benefit-
    You have to be so lost as to defy scientific scrutiny! The Canine was around before science quite happily bringing down it’s prey for consumption… Geeze another vet using the reductionist ‘scientific proof’ angle.

  7. skeptvet says:

    All of this is just to say, “Don’t think for yourself, just believe what I say.” And yet you accuse me of arrogance, which has an irony undoubtedly lost on you. Humans were around long before science too, so I hope you have given up all the useless and toxic products of science, like vaccines, antibiotics, electricity, indoor plumbing, and so on so you can live a “new life of zero problems and wonderful health, enery and vitality.” Talk about full of it…

  8. Peter says:

    Dan Scott says:
    “the…way that raw food has helped so many dogs off precription drugs and chemically laced commercial dog food onto a new life of zero problems and wonderfull health, enery and vitality.”

    The thing is, Dan, how do you KNOW that it is your raw food that has helped the dogs? Without controlled trials, without isolating variables, it could be any number or combination of changes to the dogs’ lives that produce this result.

  9. Lizi Angel says:

    I have just read your article entitled ‘Raw Meat and Bone Diets for Dogs: It’s Enough to Make You BARF’ and wanted to thank you for it (but I couldn’t see how to leave a comment).

    I am on a constant quest to find what is best and healthiest for my dogs in every respect, and over the years have fed a range of commercially produced kibbles, cans and pouches – finally settling on Acana about 2 years ago, which my dogs seem to do very on. However, I have always believed that raw food would be better, and in May 2011, after persuading my meat-phobic vegetarian husband to let me give it a try, I have been feeding my two dogs a commercially produced 75-80% raw meat/bone diet for their teatime meal (they still get Acana for breakfast).

    Their systems took to this new feeding regime without a hitch, and based on what comes out of the other end, they do just fine on one meal of kibble and one meal of raw per day. However, a few months ago, Tilly, my 5 y/o spayed JRT x Collie, started to wake up in the early hours of the morning. She sleeps beside my bed. She’d wake, become restless, pant and paw at me, then after having given her some soothing massage-type-fuss, she’d settle again and sleep for the rest of the night.

    Tilly is sensitive to certain noises such as fireworks, thunder and associated weather noise (wind blowing down the chimney, rain against the window, etc) and so for a while I thought maybe it was noise that was causing her to wake and fret, but then I started to notice a pattern – her waking time was always between 1.15 and 1.30 am. It went from 5 or 6 times a month to a couple of times a week to 2-3 nights in a row per week. What made me suspect that noise wasn’t the culprit on one particularly restless night, after I had rubbed her tummy for 10-15 minutes while she sat up in her bed, leaning against my bed, was the overpowering, sulphurous burp that suddenly erupted from the depths of her stomach, after which, she settled straight down and went to sleep. The same thing happened the next night, and the next, with the fourth and final night being particularly bad, with 45 minutes of restlessness and panting before eventually, she burped.

    The following day, I researched what could cause the production of sulphurous gas in the upper GI tract and found several possibilities, including delayed stomach emptying (gastroparesis), SIBO, Helicobacter pylori, Giardia lamblia, pancreatic enzyme deficiency, high-sulphur foods (e.g. broccoli, sweet potatoes, red meat), thiamine (vit B1) and biotin (vit H), and the protein amino acids cysteine and methionine (particularly high levels of which are found in chicken, fish and eggs). Tilly was waking like clockwork at 1.15am – 7 hours after her raw meal at teatime. She wasn’t showing any signs of discomfort or ‘sulphurous emissions’ at any other times during the day or night, and not at 3.15pm, 7 hours after her breakfast kibble. So for the past month I have stopped feeding her the raw diet for her tea and given her Acana instead, and as I suspected, immediately there was no more waking at 1.15am and no more night-time restlessness, panting or burping. Over the past couple of weeks, I have been introducing foods at teatime that have the potential to cause the production of sulphurous gas in the upper GI tract – fish, eggs, brocolli, sweet potato – with no ill effects.

    It is clear to me, that while my dogs are most definitely not overfed (I feed 25% less than rec. daily calorie intake for weight, activity, etc), Tilly was certainly getting too much of something – or maybe not enough of something. My gut feeling about the raw food has always been that at 75%-80%, the meat/bone content is too high to be ‘natural’ for the facultative, scavenger, meso-carnivore dog, but the food is ‘vet approved’ by a holistic vet who is said to know about canine nutrition, so I trusted this to be correct. But it would seem that both and mine and Tilly’s guts have proved this to be wrong – I am just extremely thankful that my dogs sleep beside my bed, otherwise I may still be none-the-wiser, and Tilly would have continued to suffer nightly, burning indigestion until this eventually gave rise to something even worse. I am also thankful that I am not so up my own bottom not to be able to change my long-held belief that raw is best, or to delude myself that any unwellness after 6 months of raw feeding must be due to something else.

    I am currently waiting for a response from the manufacturer of the raw diet and their holistic vet as to Tilly’s night-time unwellness, and certainly for the time-being I will continue to feed both my dogs Acana, for their breakfast and their tea, as I had been doing well before our little detour in raw feeding.

    Thank you again,


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  12. Amyjo says:

    As usual, the raw feeders rely on anecdotal evidence and dismiss all scientific studies as bias from the kibble industry. Do they really think the vast majority of vets, people that love animals and have dedicated their lives to the treatment, are all bought by the kibble industry? That is just plain dumb and sounds like the usual conspiracy theories.

    Fact is, NATURALLY, dogs in the wild do not have a well-balanced diet, have many growth issues/diseases as a result, and live a shorter life span as compared to dogs in homes fed a kibble diet. Cancer (in both humans and dogs) occurs naturally and has for THOUSANDS of years and will continue to increase as people and dogs live longer lives.

    As for the natural enzymes and protein BS, any biologist knows that enzymes are proteins are broken down/denatured by acids in the stomach (in both humans and dogs) such that there is negligible health benefit (and clear potential for harm) from eating raw.

  13. Betty Bell says:

    I saw about two weeks worth of raw feeders and just recently diagnosed with. H. Pylori 🙁 I was my hands a lot and I get licked on in the room by patients. I have an issue with raw feeding.

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