Pet Food Nutrition Myths

I’ve previously written an analysis of one of the most popular veterinary nutrition myths, the idea that cats and dogs should eat raw food. I was recently asked by one of my colleagues to address a couple of other veterinary nutrition myths, and by a happy coincidence Dr. David Dzanis, a board-certified veterinary nutritionist and consultant, gave a brief talk on the subject at the American Veterinary Medical Association conference from which I just returned. While I hope to someday put together a more comprehensive and thoroughly referenced list of such myths, I thought I’d share a few tidbits I learned from Dr. Dzanis, and a few other sources, on the subject of pet nutrition.


“Good” vs “Bad” Ingredients

Popular mythology assigns food ingredients statues as “good” or “bad,” ill-defined categories which are seldom based on any scientific facts but which have a powerful impact on the purchasing decisions of the pet-owning public. Unfortunately, pet food manufacturers play along and exacerbate this mythologizing of certain food ingredients for marketing advantage. When the public begins to believe a common ingredient is harmful, manufacturers will sometimes begin proudly announcing their foods are free from the ingredient, and this will appear to be confirmation of the myth. The chemical preservative ethoxyquin is a perfect example. While there is no evidence this ingredient causes any harm, and it is clear that spoilage of “preservative free” food can pose a real health risk, the ingredient is now rarely used because uninformed and unscientific public opinion demanded its removal from pet foods. A similar sort of process lead to the removal of thimersal from human vaccines despite the clear science refuting the public concerns about this preservative.

Often the growth of a movement against a food ingredient  is a purely aesthetic issue with no scientific merit. Eating chicken feet and viscera, unborn calf fetuses, and so on sounds gross, so people assume these aren’t healthy pet food ingredients. But the aesthetic standards of cats who like to chew on dead lizards and dogs who eat socks, rubber, and poop are different from ours, so it’s a meaningless way to judge such food constituents.

Such food ingredients are also disdained because of the confusion in many people’s minds of nutrients and foods. People will claim that “sea salt” is somehow different from mined salt or that wheat proteins are somehow less nutritious than beef proteins. The fact is that, properly prepared, many things we would not consider appropriate as foods in their original state can provide vital nutrients of the same quality, or better, as more aesthetically pleasing sources.

It is particularly common these days for people to claim that grains are “bad,” and that wheat and corn in particular are harmful or “allergenic” for our pets. As Dr. Dzanis puts it, “Corn and wheat are often criticized as inferior to other grains such as rice. While rice is generally more digestible than corn, that also means the starches are reduced to sugars and absorbed much more quickly. This may not be desirable for animals with clinical problems related to blood glucose control. As far as potential allergenicity, historical use of rice in therapeutic diets as a “novel ingredient” for diagnosis or control of food allergies may have led to a false impression. In cases where the cause of a food allergy has been determined, the incidence of allergy to corn is equivalent to the incidence of allergy to rice.”

The popular suspicion of wheat is likely related, to some extent, to the incident in which a Chinese firm supplying many American pet food manufacturers with wheat gluten adulterated their product with melamine, leading to kidney failure, sometimes fatal, in pets who consumed the tainted food. While this is a tragic and infuriating example of venality and inadequate regulation in China, it has nothing to do with the appropriateness of wheat as a pet food ingredient. And while a few breeds, such as the Irish Setter, have genetic gluten sensitivity, in general wheat is a healthy and nutritious ingredient perfectly appropriate as an energy and protein source in pet food.

Corn has also gotten a sinister reputation from popular author Michael Pollan. While I enjoy, and agree with, the balance of Mr. Pollan’s writing, his indictment of the corn industry and the use of corn-derivatives in food products can easily encourage an irrational and hysterical assessment that corn is somehow poisonous and nutritionally vacuous, which is simply not true. Corn and wheat proteins are common allergens for dogs and cats not because they are especially “allergenic” but simply because they are common proteins in pet food. As they are replaced, under the misguided pressure of public mythology, with rice and soy and so on, these newer ingredients will become the predominant allergens in pets who develop hypersensitivities or true allergies to commercial foods.

Hidden Food Ingredients

Pet food manufacturers are often accused of slipping roadkill, old shoes, and all sorts of other bizarre and disagreeable things into commercial pet food. While these companies exist to make a profit and certainly do what they can do encourage the public to view their products favorably, even if this involves a little slight-of-hand when it comes to describing the content of their foods, the reality is that they are legally required to identify any ingredient they use, and there is no evidence that they ignore this requirement in any routine or egregious way. Which brings me to one off the most shocking, and farfetched, concerns about pet food:

Dead Pets in Pet Food

Soylent Green is….Rover? Probably not. Promoters of this story take a few facts and weave them into an unlikely, but shocking narrative. It is true that in some parts of the country, euthanized dogs and cats are disposed of by rendering, a process which breaks whole carcasses down into potentially useful constituents. This is usually done by commercial services, and at facilities, not associated with slaughter and rendering of the agricultural animals generally used as pet food ingredient sources. however, the practice of using rendered cattle as an ingredient in cattle feed, and the subsequent epidemic of Bovine Spongiform Encephalopathy (BSE, aka “Mad Cow Disease) illustrates that there are potential risks to such practices. However, from a purely economic point of view, using rendered pets as an ingredient in pet food makes no sense. Additionally, the Pet Food Institute, an industry lobby which represents the manufacturers of  ~98% of commercial pet foods, specifically prohibits rendered pet ingredients in their members’ products.


FDA studies in 1998-2000 did find miniscule quantities of pentobarbital (2-32 parts per billion) in many commercial pet foods. This is an anesthetic often used to euthanize animals, and the finding provided some ammunition for those who claim dead pets have made their way into pet foods.

However, the same studies did not find any cat or dog DNA in the proteins from any of the tested foods. While the source of the pentobarbital was not identified, the best guess is that it comes from small numbers of cattle or possibly horses euthanized and then rendered and used in pet foods. In any case, follow up studies estimated the minimum amount of pentobarbital which has any measurable physiological effect and found that even the smallest dog eating large amounts of the food with the most pentobarbital could not get to this dose. So while the FDA cannot guarantee, that no rendered pet material ever makes it into any pet food, it is highly unlikely, and there is no evidence that even if this were the source of the anesthetic detected that there is any health risk associated with such miniscule amounts of the contaminate.

People concerned about such “toxins,” whether in food or vaccines, often fail to understand the concept of dose-dependent toxicity. As I’ve pointed out before, water and oxygen can kill in sufficient doses, despite being vital for life. And even an anesthetic which, when given as an overdose can kill, can be harmless in quantities measured in parts per billion.

The Role of AAFCO (Association of American Feed Control Officials)

AAFCO is a private organization that establishes non-binding guidelines for the production of animal feeds, including pet foods. While it is not a government agency, only government officials can be members. Most are from the U.S. but there are members from the FDA/USDA equivalents in other countries. It is often labeled, by promoters of raw or home-cooked pet diets, as an organ or lackey of the pet food industry. Industry and private groups can attend AAFCO meetings and contribute advice or information to task forces or working groups, but they cannot vote. Such groups have included pet food manufacturers, but also veterinary groups such as the Academy of Veterinary Nutrition, the American Veterinary Medical Association, and the American Animal Hospital Association, as well as advocacy groups such as People for the Ethical Treatment of Animals, Defend Our Pets, and others.

AAFCO creates guidelines and models but has no regulatory authority. However, their ingredient definitions and nutritional standards are often adopted by the FDA in their regulation of pet foods.  A food can be certified as meeting AAFCO standards based on nutrient analysis done by the manufacturer. Or it can be certified as “feeding trial tested” based on trials conducted by the manufacturer. These often last 10weeks (for growth diets) to 6 months (for maintenance diets) and involve regular clinical and laboratory monitoring. Unfortunately, a food can also be certified as “feeding trial tested” without an actual feeding trial if it is ruled by FDA substantively similar (in the same “product family”) to a food that has undergone feeding trial testing. Clearly,, this is less than ideal but without the political will to fund government testing of all pet foods marketed, these standards at least ensure a minimum level of adequacy, and they are certainly preferable to the complete lack of standards that apply to most home-cooked diets or those marketed outside the official regulatory system. Which leads me to the last category of veterinary nutritional mythology:

“Natural” and “Organic” Foods

By legal definition, to be “natural” an ingredient must come from an animal, plant, or mined source and must be minimally processed (it can be heated, fermented, and so on). Most vitamins added to foods are synthetic and do not meet this requirement. However, to be legally marketed, “natural” foods must still conform to the nutritional standards established by AAFCO and regulated by the FDA. There is zero evidence, of course, that this designation has anything to do with the safety or nutritional value of a food/food ingredient. It’s really a marketing issue, not a scientific one. The popularity of this designation is an example of the “naturalistic fallacy,” the idea that “natural” is synonymous with “good” or “healthy.” Salmonella, hydatid cyst disease, poison oak, and gamma radiation are all “natural,” while most antibiotics, antiparasitics, anti-inflammatories, and cancer treatments aren’t, but if I am unlucky to run into these “natural” things I’d sure like to have the “unnatural” ones around .

“Organic” foods and food ingredients, similarly, have a specific legal definition, enforced by USDA not FDA, that has detailed requirements for how a food ingredient can be grown and processed. The best way to ensure something is truly “organic” is too look for the USDA Organic seal. There is no evidence that food produced by these standards is superior in terms of health and nutrition. There is, however, good evidence that organic production methods have less harmful impact on the environment than more common industrial methods, so there may be some value to the designation despite its unfortunate affiliation with the mythology of the naturalistic fallacy. 




Comprehensive proceedings from the 2009 Hill’s Symposium on Nutrition Myths and Truths, Facts and Fallacies. Cats and Carbohydrates- What are the Concerns.

Cowell CS, Stout NP, Brinkmann MF, et al. Making commercial pet foods (Ingredient myths and facts). In: Hand MS, Thatcher CD, Remillard RL, et al. P (eds). Small Animal Clinical Nutrition, 4th

Edition. Topeka, KS: Mark Morris Institute, 2000; p. 141.


Food and Drug Administration/Center for Veterinary Medicine: Report on the risk from pentobarbital in dog food [Online]. Available: 31 March 2009.



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47 Responses to Pet Food Nutrition Myths

  1. Pingback: Pet Food Nutrition Myths The SkeptVet Blog | BETTER LIVES FOR PETS

  2. Bartimaeus says:

    Brian Dunning had an interesting podcast (skeptoid) this week that is related to this topic.
    He was talking about the “local food” movement and how the supposed benefit of decreased carbon footprint may not be true. He discussed Pollan’s book “The Omnivore’s Dillema” and how inefficient some local distribution models can be.
    Interesting how the “greening” of food, vaccines, etc. makes people feel good but may in fact be completely counterproductive.

  3. Rita says:

    Whilst I realise that this blog is probably not especially interested in the animal rights side of pet food issues, I find it remarkable that many pet owners, in their quest for the best for their animal completely overlook the ethics of promoting the interests of one set of (highly protected) animals over (unprotected) others – the proponents of the raw food diets seem to be the worst culprits here. At least the sub-products of slaughter which find their way in to Rover’s bowl are not creating a whole new demand for dead animals – (I’ve seen recommendations to feed fresh duck, eggs and venison to domestic dogs). The whole food, “natural”, organic etc etc etc movement tends to take over peoples’ minds, as Bartimaeus points out. The results are not necessarily less harmful taken overall.

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  5. pdx1138 says:

    This is so true. I remember not long ago Soy was getting a bad rap. It was “bad” for males to ingest it as it would cause lower testosterone. turns out that soy if processed properly (which it is for food grade) doesn’t harm at all.

  6. Heidi Junger says:

    actually, there are increasing numbers of studies documenting that (certified) organic food is more nutritious than conventional (non-certified organic food). They find significantly more minerals, vitamins, antioxidants in most all foods researcher look at. Of course, manufacturers (or you if you prepare your pet’s food) can destroy many nutrients when you bake or cook these organic ingredients. If you serve raw. your pet will get the benefits of more nutrition from organic ingredients.

    Thanks for this article and especially also for getting the distinction between ‘organic’, ‘certified organic’, and ‘natural’ pet foods right! I have seen nutrition experts get this mixed up!

  7. skeptvet says:

    Thanks for pointing us in the direction of that podcast. I’ll try to check it out. You bring up a great point, which is that any effort to make improvements in healthcare, the environment, and any othe rfield of human activity requires careful and critical thought to make sure what we end up doing really is the right thing.

    I certainly consider myself an environmentalist, and the principles of the local food movement seem basically sound, but good ideas can eaisly turn out to be mistaken, and we shouldn’t get so attached to them that we stop evaluating them critically. Ethanol from corn as an alternative to fossil fuel is an intuitively appealing idea too, but close analysis shows it to be full of holes. Environmentalism, for some reason, seems especially prone to dogmatic thinking and the naturalistic fallacy, which is a shame because it’s so clear that we need to make major changes in how we interact with the environment–just the right changes. 🙂

  8. skeptvet says:


    Great point. It can be very difficult to find an ethically consistent position with respect to pet foods. FWIW, I’m a vegetarian for a variety of reasons, including my feeling that the industrial system of meat prodction causes unecessary suffering in seeking economic efficiencies. Still, it drives me nuts when vegetarian pet owners feel obligated to impose their principles on their companion animals. I’ve seen a number of cats suffering from nutritional deficiencies because their owners tried to force their vegan habits on their pet carnivores. Their hearts may have been in the right place, but without careful thought that’s no guarantee of doing the truly right thing.

    The fact is tat such ethical questions aremore complex than most people acknowledge, and that perfect answers to them probably don’t exist. Making the perfect the enemy of the good, or committing with unquestioning zeal to simple answers is a sure recipe for nonsense.

  9. skeptvet says:


    As far as cooking and nutrient, you’re half right. Some nutrients are destroyed by cooking, and these are supplemented in commercial foods to make sure the final amount is appropriate. However, others are made more available. We cook our food not only to kill potential disease-causing organisms and parasites but also because the partial breakdown of complex carbohydrates and other ingredients by heating can make an otherwise nutrient-poor food a healthy one. The same is true for our pets.

    As for organic foods being richer in nutrients, I’ll keep an open mind but I’d like to see the research documenting that for specific nutrients, specific foods, and so on. It’s a pretty broad assertion you’lll need to support if you want us to accept it.

  10. v.t. says:

    skeptvet, this is one of the most sensible, no-nonsense, myth-busting posts on pet nutrition I’ve seen in a long time. Well done!

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  18. Just because there isn’t a double blind scientific study for something doesn’t mean its safe….or not safe to eat. I like to use common sense. Chemicals like ethoxyquin don’t seem safe….Would you drink a cupful of it?

  19. skeptvet says:

    Common sense, unfortunately, is a lousy guide to what is true and what isn’t. Is something safe or good for you because it’s “natural?” You mean like Salmonella, rattlesnake venom, uranium, and intestinal worms? Or is it bad for you because it has a complicated chemical name and had to be discovered or invented by scientists? Like antibiotics, polio vaccine, and sewage treatment?

    I agree the perfect clinical trial isn’t necessary for any and all decisions, as you will know if you read other posts here, but I agree with Mark Twain who said, “The trouble isn’t what we don’t know, it’ what we know that ain’t so!” Common sense makes us think we know things which turn out to be nonsense, and this is not the best way to make healthcare decisions.

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  26. My research on pet food nutrition is limited but I image many concepts are common with humans. I recently watched a show on how dogs have developed an ability to communicate with humans via non-verbal and verbal signals that suprases that of chimps. Apparently they’ve evolved to truly be man’s best friend so maybe it’s difficult for dog owners not to feed their “baby’s” dog food containing chicken feet even though they eat cat poop.

  27. pet toys says:

    When it comes to kibble, I think there is a wide range of quality available, ranging from poor to very high quality. I see nothing wrong with feeding commercial, kibble or canned. However, I don’t necessarily support feeding only commercial if you can keep your dog’s diet balanced. Having a balanced diet is important though and is much more complicated than just throwing some foods together and feeding it to your dog.
    As for grain, dogs do not have an absolute requirement for carbohydrates. However, I do think some carbs in the diet can be a healthy thing for most dogs. Carbohydrates can be utilized for energy production, sparing the protein content in the diet for more important functions. However, it is important to watch the calorie count. Too many of our dogs are overweight or even obese and too many carbs can contribute to that also.
    Great post though, Mary. Interesting list. Controversial for certain.

  28. speakmatt says:

    Great article. Finally someone out there who separates the facts from the BS.

  29. skeptvet says:

    Thanks, glad you found it useful!

  30. Kat says:

    This article is a myth.

    Commercial dog food is atrocious. Most of the foods are made from food unfit for human consumption. Deny it all you want, but that’s a fact. I don’t feed my family, nor my family dogs food unfit for consumption.

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  32. sharron says:

    i would like to know, since when did dog food have to be suitable for human consumption? please correct me if i am wrong in my understanding of this. so what people are saying is that the dog food must be really healthy if humans are able to eat too. when did we start comparing humans to dogs. i feed my yorkie/chihuahua hill’s healthy advantage and she she is doing really well on it. i’m not saying that other foods bought at a pet store are bad, just saying that this food so far is the only dry food she will eat without having to add to it to get her to eat it.

  33. DianeM says:

    Skeptvet, a Yahoo group I belong to on the subject of conservative management for CCL ruptures recently got onto the subject of whether commercial pet foods contain euthanized pets. The following article was referenced as “proof” that they do. There are some interesting rebuttals in the comments, but I would appreciate hearing your input if you have a chance. I’ve suggested to members of the group that they come to your blog for quality information on this an other topics.

  34. skeptvet says:

    I am not aware of any additional data to answer this questions since the FDA study nearly 15 years ago that Dr. Khuly and I both reference. What I can tell you is:

    1. Putting euthanized dogs and cats into pet food is illegal.
    2. All U.S. pet food manufacturers have pledged not to do this.
    3. Economically, it would make no sense to use dead pets for pet food because the miniscule numbers that could be obtained illegally without detection would not be worth the risk and trouble given the enormous volume of rendered animal material needed to produce a commercial pet food.
    4. The FDA study found no evidence of dog or cat DNA in the pet foods tested. There was a very small amount of a barbiturate used for euthanasia detected in some of the samples. The FDA believed this was due to the presence of euthanized horses in the feed material. Dr. Khuly is skeptical of that. I have no additional evidence, but I have no reason to doubt the FDA’s explanation.

    At this point, I think it very unlikely that euthanized dogs and cats are routinely used as source material for pet foods. There is no evidence to suggest this is a common practice, and no evidence to suggest any health problems that could be explained by this. It is impossible to prove beyond a shadow of a doubt that no rendering plant ever incorporates any dog or cat bodies into material that ends up in the pet food source stream. But the issue is not whether it is conceivable that this could happen, it is whether it happens routinely or presents a health risk, and for that there is no evidence, only rumor.

    People who are concerned about the theoretical possibility can certainly choose alternative food sources, but they have to be aware of the risks and problems associated with these as well. Simply feeding a haphazard mixture of fresh foods without guidance from a nutritionist is far more likely to present a health risk to their pet than feeding a commercial pet food.

  35. DianeM says:

    Thanks for the quick, thorough response. Quite a few folks claim that animal shelters send their euthanized animals to rendering plants. I’m guessing this is what really helps keep the rumor alive, because that would be a more significant source of animals. But if those remains are being sent to rendering plants, they would have to be rendered into products other than pet food, since cat and dog DNA hasn’t been found in pet food.

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  37. KDub says:

    Thanks for such a great writeup! Always great info! I do have a question reguarding this claim:
    ” There is, however, good evidence that organic production methods have less harmful impact on the environment than more common industrial methods,…”
    Do you have any citations for this? I was under the impression this was not the case but would be open to new information! Much appreciated!

  38. Kaz says:

    I don’t know.

    But I can’t help but wonder whether you’d drink a cup of dihydrogen monoxide.

  39. skeptvet says:

    I’m honestly no longer certain this is true. I believe the benefits and tradeoffs are actually quite complicated. There may be less use of some pesticides, for example, but greater use of others, less use of synthetic fertilizers but then more nitrogen runoff from manure, some local benefits but then greater unit costs due to lower productivity, etc. I don’t know that I can take a position on this either way at this point. Do you have any relevant resources you would suggest on this subject?

  40. Me says:

    I’m glad to see you address this as well. Organic pesticides are often very broad spectrum, and require greater amounts and more applications than many of their synthetic counterparts. Same for herbicides, fungicides, etc.

    Likewise for amounts of organic fertilizers, which still pollute bodies of water and require much more raw ingredients to process in order to turn into fertilizers.

    Many organic products aren’t highly effective and this leads to less productive yields of crops due to pests and diseases.

  41. Ron says:

    I was not sure if this was posted as of yet, but thought I would add it, juts in case.
    I get alerts when food is recalled and for what reasons, at times I do miss the , but this one caught my eye.
    Pentobarbital a drug known to be used in animal euthanasia .

  42. skeptvet says:

    Yes, there is an ongoing investigation into this episode. The latest theory is that euthanized horses may have gotten into the supply chain since horse DNA may have been detected in the affected foods, but the FDA hasn’t confirmed this. The preliminary report form the FDA seems to indicate a lot of violations of safety standards at the meat suppliers involved.

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  44. Jenny says:

    Do you know if the FDA studies about the euthanasia and companion animal content are still available somewhere? The hotlink seems to be outdated

  45. skeptvet says:

    Here’s a link that is working.

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