"A founding premise in popular lay publications and on the Internet regarding RMBDs [raw meat-based diets] is that these are the diets that wild, nondomesticated dog and cat species ate during their evolution into pets, which may provide an important rationale for some owners to feed these diets to their dogs and cats. Cats have remained obligate carnivores during domestication, and their natural diet includes a range of small prey species such as mammals, reptiles, birds, and insects that can be hunted, captured, and eaten by the cats. Conversely, dogs have adapted to eating an omnivorous diet and can consume a variety of plant and animal products to meet their essential nutrient requirements. However, both cats and dogs are able to digest and metabolize many nutrients provided from plant-based ingredients. Additionally, dogs have undergone an incredible variety of selection pressures resulting in large phenotypic differences from their ancestors and among current breeds. In fact, it was reported that there are 36 regions of the genome that differ between dogs and wolves, 10 of which play a critical role in starch digestion and fat metabolism. The authors of that study conclude that these genetic differences in the genome between dogs and wolves and hence the ability to digest starch and fat constituted a crucial step in the early domestication of dogs. Therefore, even if the typical diet eaten by a wild, non-domesticated dog or cat can be considered optimal for reproduction and survival in those animals, in which the lifespan is typically quite short, these diets may not be optimal for domestic dogs and cats living in a home environment, with owners who anticipate that their pets will have long and healthy lives." (Freeman et al 2013)

So the arguments rage, not about verifiable facts, but about opinions, perceptions, anecdotal experiences, myths, and folklore. If you look up "raw feeding" on Wikipedia, you will see an odd caveat at the top of the page:

"This article contains weasel words: vague phrasing that often accompanies biased or unverifiable information."

Yep, that about sums it up.

One meme that appeared in the discussions of my post that unfortunately included the word "diet" in the title was the oft-repeated notion that "we don't know much about ____ diet because nobody wants to pay for the research, least of all the commercial dog food companies." Well, in fact, there IS information about non-commercial diets for dogs if you take the time to look.

A 2013 study performed a nutritional evaluation of 200 homemade diets made from recipes published in books (including pet care books and veterinary textbooks), on the internet, and other sources. About 65% of these were written by veterinarians. Of these, only four (4!) were nutritionally complete, and those were designed by veterinary nutrition specialists.

"Most (184 [92%]) recipes contained vague or incomplete instructions that necessitated 1 or more assumptions
for the ingredients, method of preparation, or supplement-type products. Supplement-type products were not included in 58 (29%) recipes. Most (169 [84.5%]) recipes did not provide specific feeding instructions; instead, some included general instructions to modify amounts on the basis of each individual pet’s size and body weight (including any patterns of weight gain or loss). Similarly, most (171 [85.5%]) recipes did not provide calorie information or the target body weight for a pet. Additionally, some sources provided recipes that differed widely in calorie content for the same-size pet. Thirteen (6.5%) recipes included garlic or onion, which are foods associated with hemolytic anemia in dogs.

Many proponents of less structured recipes for home-prepared diets assert that although each day’s
meal is not necessarily complete, rotation and variety will provide a balanced diet overall. Our analysis indicated
that this assumption was unfounded because evaluation of 3 recipe groups, each of which comprised 7 separate recipes, did not eliminate deficiencies. In addition, many recipes had similar deficiencies, with 14
nutrients provided at inadequate concentrations in at least 50 recipes. Thus, even the use of a strategy for
rotation among several recipes from multiple sources would be unlikely to provide a balanced diet. A greater number of recipes written by nonveterinarians had deficiencies, those recipes had significantly (P = 0.001) more nutrients that were deficient, and the deficiencies were more severe, compared with results for recipes written by veterinarians (Table 2). The lower number of deficiencies per recipe in those written by veterinarians may have been associated with a better understanding of canine nutrition by veterinary professionals, although most of the veterinarian-written recipes had at least 1 nutrient deficiency. Only 4 recipes written by board-certified veterinary nutritionists were available for evaluation; all 4 had nutrient profiles that were within the AAFCO-recommended ranges for an adult canine maintenance diet." (Stockman et al 2013)
​
Note that the authors state that while 129 (65%) of the recipes they tested were written by veterinarians, only 4 were nutritionally complete. If the veterinarians aren't getting it right, it's clear that there is a need for better, more accessible information for both owners and their veterinarians.

The other thing ICB would like to do is create an evidence-based course in canine nutrition. There is clearly a need, and we'll be talking with some veterinary nutritionists to get help putting something together that will address many of the issues dog owners have to grapple with when they worry about what to feed their dogs. We will also see if we can have some of the relevant published studies made more freely available instead of locked down behind a pay wall. (There is a link to a free download of one of the studies cited here in the References below.)

Veterinary schools have board certified nutritionists that offer both free and fee-based information and consulting to both dog owners and veterinarians. They can provide general information about commercial and home made diets (e.g., what should you feed a nursing bitch?), and they can also design a custom diet specific for your dog's age, medical conditions, allergies, and your personal preferences about feeding. There are links to these resources at the bottom.

There is a great online tool, "Balance It", for assessing the nutritional quality of the diet you're feeding your dog, and it will recommend how a diet should be modified to be nutritionally balanced. Or, you can use it to design a custom diet for your dog from scratch, using the specific ingredients you select (like the moose and canned pineapple, yummm!). This tool uses the same algorithms the veterinary nutritionists use to evaluate diets, so it's a great (and free!) resource for dog owners. They also sell some supplements to fill in the gaps of your recipe if necessary.

By Carol Beuchat PhD

(NOTE 1: For those that just read the first sentence or two before typing a rebuttal, this post has nothing to do with cancer.)

(NOTE 2: There is nothing here that endorses a commercial diet, so no need to write a rebuttal about that either.)

(NOTE 3: If the comment you're going to write starts with "I haven't read it yet, but...", just stop. Read it first. It doesn't say what you think it does.)

(NOTE 4: Before you fire off a rebuttal about anything else, download the paper towards the bottom with the bannerhead "Timely Topics in Nutrition", which addresses many of the comments that are likely to come up in responses. Please.)

(NOTE 5: The title is new and improved. More about this in a future post...)

I got a flood of interesting feedback from my post asking if rates of cancer are higher in dogs than other mammals. Mostly, people had objections of one sort or another about the data - no control for how often the animals are screened,  no information about whether the dogs were dying young or old, no consideration of wild vs domestic animals, and so on. The other category of responses was explanations for the data, and here there was clearly a theme: dogs have higher rates of cancer because of a) diet, b) vaccines, and/or c) environmental toxins. I will do a separate blog post about these topics because they are worth addressing, as well as some background on the process of science and why it is useful to toss together a bunch of data with obvious issues in the first place.

But this morning something popped up on my Facebook feed that prompted me to take the time to address one aspect of the diet issue. It was a photo of a 3 month old puppy of a good sized breed, cute as a button, and proudly introduced as "raw fed". Now, I suspect that those that suggested diet as a cause of cancer in dogs believe that commercial, processed foods are the problem and that a raw diet is better for dogs. I have never seen any studies that document commercial dog food as a risk factor for cancer, except perhaps as incidental to obesity, but that doesn't rule it out. On the other hand, I have seen many studies that looked at other risk factors associated with raw diets, and most noted that bacterial contamination of raw meat is common. I'm sure you all know that.

But the raw fed puppy highlights a very serious problem that I suspect many don't consider when they lovingly whip up a batch of their home-formulated diet, and that is the difficulty in providing a diet that is nutritionally complete, especially for a puppy. Fortunately, there is published information about the problems this can cause. Here are two examples.

Below is information about the diet of the Saint Bernard puppy, the recipe used and the nutritional analysis compared to dietary recommendations. 

This Saint Bernard puppy was getting only 27% of the recommended minimum level of calcium for growth in dogs. Look at the cascade of problems this caused.

Shetland Sheepdog (8 months)
​This Sheltie was fed a commercial dried food, Sojos European Style dog and cat food mix, to which the owner added raw hamburger.
​

I try to stick with genetics here, but the sorts of problems that sent these pups to the doggie hospital could have been mistaken for genetic problems. It should be clear that especially for puppies, getting the diet wrong by even a little can have significant consequences. As the authors in these two papers recommend, get the diet you're using tested at a laboratory to make sure that it contains the right nutrients in the right balance. And don't assume that the advice in the "everything natural" magazine is correct; check with your veterinarian and do your own homework.

A good place to start are these papers about risks and benefits of raw diets, and the nutritional guidelines for dogs and cats.

Two very interesting papers have appeared this week that are getting lots of buzz in the press about cancer in elephants - or rather, why elephants don't get cancer. One has just been published and the other has been submitted for review but is available online (see below); together they offer up a fascinating story.

There has been a paradox stewing for decades in the scientific literature about why large animals that have more cells and live longer don't also have an increased risk of cancer. The logic says that every time a cell divides, there is opportunity for a mutation to occur; so in larger animals that have more cells and also live longer, we should expect to see higher rates of cancer. But this is Peto's Paradox: rates of cancer don't seem to vary with body size at all, and in fact the cancer rate is especially low in the world's largest land mammal, the elephant (Peto et al 1975). How can this be?

What I really wanted to know was how cancer rates in dogs compare with those of mammals in general. I used the data from a paper about breed predispositions to cancer published in 2013 (info here), dug out some data for body weight of dog breeds, and created a graph comparable to the one above for all mammals. (Note that these data are for a European population of dogs, and the same breeds might have higher or lower cancer statistics in other subpopulations; Golden Retrievers, for example, have a cancer rate of about 60% in the US; see Hoven.)

To look at this question, I've taken the data for mammals and dogs and superimposed them both on a single graph so they are easy to compare. (The dog data get all smushed together because the x-axis is on a log scale and the range in body size of dogs is much less than for mammals in general.)

This is not a happy picture, and it answers the question very clearly. Yes, rates of cancer in dogs are higher- spectacularly so, in fact - compared to those for mammals in general. Cancer rates in other mammals are largely less than 20%, while in dogs there are only a handful of breedsin that range, and there are none at all lower than about 15%, where most of the mammals are. In fact, the Tasmanian Devil with its contagious cancer is matched by the Flatcoated Retriever and even outdone by the Irish Water Spaniel, with a half dozen more breeds almost as high.

Cancer is a problem not just in a few dog breeds but in many. Cancer rates of 20% or 30% are taken as "normal" because they are so much lower than the levels in breeds that are notorious for cancer - the ones up at 50% and 60%. Clearly, however, what is considered normal for dogs is much higher than what we see in mammals in general, and cancer rates that are "abnormally high" in dogs are actually off the charts.

Quite a bit of money is being spent on canine cancer research. Most of these studies focus on exploring possibilities for earlier detection and better treatment, both of which could do much to improve the lives and lifespans of dogs diagnosed with cancer, and they usually focus on one or a few specific breeds in which cancer rates are (perceived to be) high. But these data for dogs, especially in the context of information for mammals in general, suggest that there is a systematic problem here that is related somehow to body size: larger dogs have more cancer. Not only is there a stark difference in rates of cancer of dogs compared to other mammals of the same size, but there is also a clear difference between small and large dogs. Why? Maybe it has something to do with growth hormones (I have mentioned this here). Perhaps this is the manifestation of Peto's Paradox. We don't know because as far as I know, nobody is addressing the problem of cancer from a broad perspective that recognizes these patterns in the data.

A few clever scientists, knowing a bit about cancer in other mammals, have discovered a really interesting thing about the genomes of elephants that makes them especially resistant to cancer, something that tells us a bit more about the biology of cancer in all animals. I think dogs have much to tell us about this awful disease if we back away from addressing it as a breed problem resulting from genetic bad luck, and instead see it as evidence that there might be some unknown but fundamental process that is driving the risk of cancer in dogs. We just need to figure out what it is.

Abegglen LM, AF Caulin, A Chan, and others. 2015 Potential mechanisms for cancer resistance in elephants and comparative cellular response to DNA damage in humans. JAMA ( doi:10.1001/jama.2015.13134). (pdf)

Peto R, FJ Roe, PN Lee, L Levy, J Clack. 1975. Cancer and ageing in mice and men. Br. J. Cancer 32: 411-426.

Sulak M, L Fong, K Mika, and others. MS. TP53 copy number expansion correlates with the evolution of increased body size and an enhanced DNA damage response in elephants. BioRxiv (doi: http://dx.doi.org/10.1101/028522). (pdf)