A Critique of Dr. Jean Dodds’ Chapter 5
Pet Food Preservatives and Other Additives
 

By Rosalind Dalefield BVSc, PhD, DABVT, DABT*
 

This short chapter, which I found to be rather patchy and erratic in its narration and reasoning overall, has several major flaws. Most of these can be summarized under the following headings:
 
 

Principles of toxicology ignored

Very basic principles of toxicology were succinctly expressed by Paracelsus (1493-1541) when he wrote "All substances are poisons: there is none which is not a poison. The right dose differentiates a poison from a remedy." It might also be accurately said, “the right dose differentiates a poison from a useful food additive.” Dr. Dodds ignores this very basic principle in her lengthy discussion of ethoxyquin. Potential toxic effects of ethoxyquin are listed, but the doses at which these effects may be observed are not given. We are told that ethoxyquin crosses the placenta, but we are not told at what dose this occurs. Many chemicals that can cross the placenta do not do so at low doses because they are detoxified by the mother before they reach the placenta. We are told that ethoxyquin can alter hepatic vitamin A levels, but we are not told at what dose this occurs. All poisons have thresholds below which toxic effects do not occur. Dr. Dodds asserts “Continuous exposure to this potent antioxidant [ethoxyquin] in preserved foods poses the risk of chronic low-level effects.” That statement is quite simply wrong, provided the continuous exposure is always below the threshold for chronic effects, usually characterized as the chronic No Observed Adverse Effects Level (NOAEL).

Dr. Dodds also states:

Synthetic antioxidants are substrates for cytochrome P-450, which affects hydroxylation of foreign substances and drugs (refs). A consequence of the body’s diminished ability to hydroxylate is its reduced capacity to detoxify and excrete toxic and pharmacologic compounds.

In further examples, Dr. Dodds refers to potential carcinogenic effects and the potentiation of other chemicals by synthetic antioxidants, but fails to indicate what doses are required to elicit these effects. It is impossible to assess the significance of these effects without knowing whether the concentrations of these chemicals in commercial pet foods even remotely approach the doses required to elicit the effects. After all, numerous natural chemicals, found in normal human diets, can be shown to be carcinogens, but pose no risk at normal doses. Some examples may be found in the erudite papers of Bruce Ames and colleagues:

Carcinogen Research

Dr. Dodds abjectly fails to demonstrate that synthetic antioxidants are hazardous at doses normally ingested in commercial pet foods but then, she does not even try.

Unreferenced assertions

The referencing in this chapter is very uneven. While some statements are backed up by numerous citations, several of the most startling and provocative statements are completely unreferenced.

For example Dr. Dodds writes of “Apparent increases in the number of humans and animals with disease states affecting immune function and thyroid metabolism” yet appears to provide no references to document such alleged increases. Some references half a paragraph later may possibly be intended to cover these claims, but they are citations of papers in medical journals, not veterinary journals. So the claim appears to be unreferenced, at least as far as animals are concerned.

It has been said that extraordinary claims demand extraordinary evidence. A claim of increases in immunologic disorders and of thyroid metabolism (which make together an enormous and diverse field) should be thoroughly referenced, including good evidence that the increases are not merely due to better diagnosis.

Another such sweeping, totally unreferenced assertion is “Autoimmune or immune-mediated diseases are a major threat to humans and animals throughout the world.” Really? Do autoimmune disorders really rank with killers of mankind such as malaria (which may have killed as many as half of all the people who have ever lived, and strikes people with perfectly healthy immune systems) and malnutrition, or compare with starvation and predation as killers of animals? It is a great pity that this very startling assertion is unreferenced.

Nor are references given to back the assertion that “Thyroid dysfunction…of dogs and cats… has increased in frequency over the last decade” or the assertion that in the case of animals with “immunologic dysfunction,” “their exposure to unnecessary drugs, toxins and chemicals should be minimised.” This is a pity. I would be very curious to know the reason behind the latter assertion. I would have thought that exposure to infectious pathogens would be the major concern for animals with immunologic function.

Other important claims which should be supported by references, but are not, include:

Experience has shown that families of dogs susceptible to thyroid and other autoimmune diseases show generalized improvement in health and vigor when fed premium cereal-based diets preserved naturally with vitamins E and C (without the addition of synthetic antioxidant preservatives).

Challenging the immune system of animals susceptible to these disorders [thyroid and other autoimmune diseases] with polyvalent modified-live vaccines has been associated with adverse effects in some cases.

An important consideration, however, is the cumulative antioxidant load, because use of BHA or BHT to preserve the animal fat sources in these foods is additive to the ethoxyquin incorporated into the finished product.

Illogical statements and arguments.

Dr. Dodds includes a long passage on the importance of iodine and selenium levels without providing any evidence whatsoever that the levels of I or Se in commercial pet foods are inappropriate. She then finishes this section with the claim “Feeding only home-cooked fresh, natural ingredients is a logical way to minimize this potential risk.” This is not, in fact, logical at all. There are absolutely no grounds to conclude that “home-cooked fresh natural ingredients” would guarantee appropriate I and Se levels. In fact it would be a straightforward matter to create diets containing toxic levels or extremely deficient levels of either element or both elements. For example fresh, natural kelp could provide excessive iodine and has done so, causing teratogenic effects in foals, while fresh, natural Astragalus is a good example of a source of toxic selenium levels.

In the same vein, the statement… “Owners who prefer to use natural, fresh and wholesome ingredients…” begs the question: Who says natural and fresh means wholesome?

Dr. Dodds makes the sweeping statement “Wholesome nutrition is the key to maintaining a healthy immune system and resistance to disease,” but then tries to support this opening statement by giving examples of various inherited diseases of highly inbred breeds, such as inherited copper storage of Bedlington terriers. Most of the problems she cites are not immunopathies. Furthermore, it is not logical to extrapolate from such animals to the population at large. To do so would be equivalent to making dietary recommendations for all people to eat the special diets required by phenylketonurics. She also attempts to back her opening statement with examples of nutritional diseases of genetically normal animals, including hip dysplasia, osteochondrosis dissecans, and hypercholesterolemia. Again, none of these are immunopathies.

In the summary section, Dr. Dodds makes this statement:

Also needed is an evaluation of their [synthetic chemical additives and other pet-food additives] interactions with other genetic and environmental factors that affect the health and performance of companion animals, with particular emphasis on those that are inbred or closely linebred.

Incorrect statements and misquoted references

Dr. Dodds makes the rather extraordinary statement:

Excessive supplementation of any nutrient can lead to significant clinical problems, many of which resemble the respective deficiency states of these ingredients

On closer inspection, the references for this startling statement refer solely to selenium and vitamin E, so this is also an example of misuse of references.

Another example of a misquoted reference is found associated with the statement:

Ethoxyquin, BHA and BHT …have been shown to increase the toxicity of other chemicals but also their mutagenicity, sensitivity to radioactivity exposure, and tumor yield from chemical carcinogens

Self-citation and frivolous citation

There is absolutely nothing wrong with self-citation when one is citing a piece of original research one has previously published when it supports a point one is trying to make. However, it is disingenuous to cite one’s own previous reviews and book chapters. This amounts to writing “Because I’ve written the same thing in the past, it is therefore true”. Citations which turn out to be in journals that are not peer-reviewed or, worse still, are glossies for pet owners (Dog World appears in the references three times) also invite the cynicism of any serious scientist.

Use of outdated theory

Dr. Dodds appears to be applying the Immune Surveillance Theory when she states that:

…chemicals that promote immune suppression or dysregulation and oncogenesis may contribute to the failure of immune surveillance mechanisms protecting the body against the vast array of infectious and other agents that induce immunologic or neoplastic change.

Subscribing or appearing to subscribe to an outdated and discredited theory does not have a favourable effect upon one’s credibility.

Excessive speculation

Much of this chapter is highly speculative. The paragraph quoted immediately above is a good example. Another can be found in the section on ethoxyquin, in which we are told that “Other downstream effects can be predicted.” Surely we can, and should, do better than predicting these effects before we condemn ethoxyquin? They should be demonstrated and, most importantly, the minimum dose at which they occur should be established. The same also applies to Dr. Dodds’ speculations about the effects of ethoxyquin on steroid hormones. To quote Sherlock Holmes, ‘It is a capital mistake to theorise before one has data’ (or perhaps “The temptation to form premature theories upon insufficient data is the bane of our profession.” would be a better Holmesian quotation).

Further speculation is encountered in the passage:

It is tempting to speculate that the rising incidence of leukemias, lymphomas, hemoangiosarcomas, and chronic immunosuppressive disorders among companion animals is due at least partially to the widespread use of chemical antioxidants and other additives in commercial pet foods.

One might also ask, why then have the incidences of almost all cancers of humans in the United States either declined over the last few decades or held steady? The few that have increased are due to identified factors such as sunbathing or AIDS infection. Why are dietary chemical antioxidants and additives not causing an explosion of neoplasia in human beings?

Emotive language and unbalanced coverage.

Terms such as “natural” and “wholesome” are often used emotively in this chapter. For example, the leading commercial pet food manufacturers would be justified in being affronted at a sentence such as:

From a holistic approach to health, fresh, wholesome, well-balanced foods composed of natural ingredients are preferable to commercial diet formulas, which are primarily cereal-based and include a wide array of additives intended to provide “complete nutrition.

It should also be remembered that pet foods made and stored at home may also contain “natural ingredients” including a host of bacterial toxins and mycotoxins which are not wholesome at all. There appears to be an assumption that “natural” means “beneficial” which is simply untrue, as anyone who has seen a clinical case of hypervitaminosis A in a cat, resulting from a totally “natural” home-made diet based on liver, can confirm.

Dr. Dodds also uses emotive language such as “We should not be afraid to challenge the industry…” Why are these fighting words necessary? The industry will serve itself and its shareholders best by maximising the health and wellbeing of the target consumers and their owners.

She also asserts that “Veterinarians should be…encouraged to seek and recommend commercial or home-made pet foods and pet food companies that promote a more holistic approach to food safety,” but she fails to explain why. Why not seek and recommend pet foods made on the basis of sound science instead?

Overall, this chapter is extremely biased. There is no discussion of such issues as the possible deleterious effects of “natural” preservatives (such as salt, for example), or the adverse effects on palatability and health of rancid food, or the risks of mycotoxins or bacterial toxins. Dr. Dodds does not discuss the negative aspects of home-cooked diets, such as the greater pressure on a pet-owner’s time or the numerous cases of clinical deficiencies and toxicoses that have resulted from home-prepared pet foods. She mentions only very briefly that “natural” preservatives tend to be more expensive and less effective without discussing the impact of this on pet-owners who are on limited budgets. It seems distasteful for a high-paid professional such as a veterinarian to deal so dismissively with this problem. The joys of pet ownership are not, and should not be, solely the preserve of the wealthy.

It is noteworthy that Dr. Dodds admits that moves on the part of the pet food industry to replace synthetic preservatives with natural ones have been made in response to “consumer and professional queries” and the beliefs (not the scientific evidence) of “proponents of natural antioxidants.” In other words, these changes are not attributable to any scientific evidence that synthetic preservatives are harmful in any way at the concentrations used in commercial pet foods. Sadly, the spectacle of industries buckling under pressure from ignorant victims of rumour and speculation, is not an unusual one. It does not mean, however, that the scare-mongers are right or that the industry was previously in the wrong.

Closing comments

At the end of the chapter I found a statement with which I agree wholeheartedly:

The industry needs additional short- and long-term controlled feeding trials that incorporate modern toxicologic, medical and epidemiologic assessments of synthetic chemical preservatives and other pet-food additives.

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*Rosalind Dalefield BVSc MRCVS PhD
Diplomate, American Board of Veterinary Toxicology http://www.abvt.org
Diplomate, American Board of Toxicology http://www.abtox.org
URL: http://www.dalefield.com/toxicology