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: http://www.fda.gov/cvm/FOI/DFreport.htm. 31 March 2009.