Nutrition is one of the most frequent subjects my clients want to discuss, and often one of the most controversial. Raw diets,1 vegetarian or vegan pet foods,2 ketogenic diets for pets,3 the significance of “artificial” versus “natural” pet food ingredients,4 and the fundamental question of whether veterinarians are trusted counselors when it comes to nutrition are just some of the controversies in pet nutrition I have covered in Veterinary Practice News.
These are all tough issues, both because of the passionate opinions they engender and because of the inevitably limited and imperfect scientific evidence available to adjudicate them. A key tenet of evidence-based medicine, however, is that we have to make judgments based on the evidence we have, not the evidence we wish we had. Another core principle is that our confidence in any judgment we make should only be as strong as the evidence allows.
Today’s topic is one where claims and passions far exceed the available evidence—fresh pet food. Various terms are used to describe such diets, including fresh, lightly-cooked, whole-food, etc., and there is no standardized terminology for these diets. I will mostly use “fresh food” as a shorthand for the myriad diets marketed in this way.
In addition to homemade fresh diets prepared by individual dog owners, a number of companies are now selling cooked commercial diets that are designed and packaged like fresh, homemade foods rather than extruded kibble or traditional canned pet food. These companies market such diets with implicit, or often explicit, claims that they are healthier than traditional commercial foods.
In an extreme example, the founders of Just Food for Dogs (JFFD) have written a polemical book titled “Big Kibble: The Hidden Dangers of the Pet Food Industry” to promote their alternative to traditional commercial diets. They have not been restrained or respectful in their response to criticism of their claims and marketing methods. The company explicitly claims their product is healthier that traditional kibble, and the leaders are not impressed by calls for evidence to prove this: “The mainstream veterinarian needs research and proof that real food is healthier, and that just boggles my mind,” Dr. Chavez adds. “We’re the last healthcare profession that is recommending an ultra-processed daily sustenance. It’s just crazy.”
So, is it crazy to wonder if fresh foods really are healthier than canned or kibble? Can we assume that dogs eating traditional commercial diets will have shorter lives and more health problems than dogs eating fresh diets? Regular readers of this column will already know my answer—nope! Equally “obvious” claims about the complicated relationship between environmental factors and health outcomes have been stunningly wrong many times in the history of human and veterinary medicine, and we should place very little confidence such beliefs without scientific evidence.
The ideal evidence for these claims, of course, would be long-term comparative feeding studies showing dogs eating fresh diets live longer and experience less disease than those eating kibble or canned foods. Such studies would be extremely complex and expensive to run, and I don’t see much chance companies on either side of the debate will step up to support them. This means that, as usual, we need to rely on less robust evidence (and proportion our confidence accordingly).
There is certainly epidemiologic evidence that consumption of whole foods, particularly fruits and vegetables, is associated with improved health outcomes in people compared with packaged and convenience foods. But it needs to be emphasized that commercial dog food is not the nutritional equivalent of potato chips just because both come in bags. Human snack and convenience foods are deliberately designed to be appealing, not nutritious. Pet foods are formulated with much more emphasis on nutritional value, and have been used and evaluated extensively for decades for their impact on health. They may well not be the optimal food we should be feeding, but they are hardly the egregious poison their detractors claim. And as the analogy breaks down, so does the relevance of the epidemiologic evidence in humans to pet feeding practices.
There is little direct research on the potential health impact of fresh diets compared with other cooked pet foods. There is research showing that homemade diets are often nutritionally unbalanced and incomplete, but little evidence pertaining to commercial cooked fresh diets.5–10
A small study was reported as a poster at the 2014 American Academy of Veterinary Nutrition Research Symposium, and this is often cited by fresh food advocates as positive evidence for their claims. Twenty-one dogs of various breeds were transitioned from kibble to a frozen cooked fresh-food diet and basic bloodwork and exams were conducted at the beginning of feeding the diet and again at 6 months and twelve months later. This was a pilot study, so there was no control group, no blinding, no pre-specified outcomes or hypotheses, no reported accounting for repeated measures or multiple comparisons in the statistical analysis, no discussion of any other aspects of the dogs’ health or environment, and overall no significant control for bias or random error. This limitation is especially relevant given that the lead author is Chief Medical Officer for JFFD and also an author of the book I mentioned earlier.
A few differences were found in some clinical laboratory measures before and after the transition to the JFFD diet. Increases were seen in red blood cell count and globulins, for example, though all values remained within reference intervals for all dogs. This sort of data might suggest hypotheses for future testing, but it doesn’t support any specific conclusions about the relative merits or health effects of different types of diet. It certainly does not support the claims in a JFFD press release that their foods “could benefit immune health” and that if the purported trends in the blood values continue for a lifetime “we may see a decrease in chronic diseases such as cancer, renal failure, kidney disease, inflammatory bowel disease, dental disease, etc.”
There is some laboratory research showing fresh diets have higher digestibility than extruded pet foods, and there may be effects on gut flora and other physiologic parameters.11–14 However, these are, once again, only useful bits of data that suggest testable hypotheses, not conclusive evidence for real-world health effects.
Personally, I am sympathetic to the hypothesis that pet diet which contain less processed whole ingredients may be superior to conventional canned or extruded dry diets in terms of health outcomes. The epidemiologic evidence in humans, and pre-clinical research in laboratory animal models is suggestive, though by no means conclusive. There are, of course, other issues besides health impacts that must be considered in comparing the merits of different types of pet food. The affordability and accessibility of different diets, storage and stability, safety, environmental sustainability, and many other factors are relevant as well to the recommendations of veterinarians and the feeding choices of dog owners.
The bottom line, as always, is that we should make decisions based on the best possible evidence, and we should limit our claims and confidence to what the evidence can support. Currently, the most optimistic assessment of diets identified by marketing materials as fresh, lightly-cooked, whole-food, human-grade, etc. is that it is plausible they may have health benefits if properly formulated by veterinary nutritionists and properly handled and fed by owners. Biologic plausibility and pre-clinical evidence are necessary starting points, but evidence from the real world on meaningful health outcomes will be needed before we can have any confidence in claims about the benefits of such diets.
1. McKenzie BA. Debating Raw Diets. Vet Pract News. January 2019:30-31.
2. McKenzie B. Are Vegan of Vegetarian Diets Good for Pets? Vet Pract News. July 2019:26-27.
3. McKenzie BA. Is Keto Kind to Pets? Vet Pract News. January 2020:30-31.
4. McKenzie B. Is banning “artificial” ingredients based on fear or science? Vet Pract News. March 2019:36-37.
5. Lauten S, Smith T, Kirk C. Computer analysis of nutrient sufficiency of published home-cooked diets for dogs and cats [abstract]. J Vet Intern Med. 2005;19(3):476-477.
6. Heinze CR, Gomez FC, Freeman LM. Assessment of commercial diets and recipes for home-prepared diets recommended for dogs with cancer. J Am Vet Med Assoc. 2012;241(11):1453-1460. doi:10.2460/javma.241.11.1453
7. Larsen JA, Parks EM, Heinze CR, Fascetti AJ. Evaluation of recipes for home-prepared diets for dogs and cats with chronic kidney disease. J Am Vet Med Assoc. 2012;240(5):532-538. doi:10.2460/javma.240.5.532
8. Taylor MB, Geiger DA, Saker KE, Larson MM. Diffuse osteopenia and myelopathy in a puppy fed a diet composed of an organic premix and raw ground beef. J Am Vet Med Assoc. 2009;234(8):1041-1048. doi:10.2460/javma.234.8.1041
9. ROUDEBUSH P, COWELL CS. Results of a Hypoallergenic Diet Survey of Veterinarians in North America with a Nutritional Evaluation of Homemade Diet Prescriptions. Vet Dermatol. 1992;3(1):23-28. doi:10.1111/j.1365-3164.1992.tb00139.x
10. Pedrinelli V, Gomes M de OS, Carciofi AC. Analysis of recipes of home-prepared diets for dogs and cats published in Portuguese. J Nutr Sci. 2017;6:e33. doi:10.1017/jns.2017.31
11. Oba PM, Utterback PL, Parsons CM, Swanson KS. True nutrient and amino acid digestibility of dog foods made with human-grade ingredients using the precision-fed cecectomized rooster assay1. Transl Anim Sci. 2020;4(1):442-451. doi:10.1093/tas/txz175
12. Do S, Phungviwatnikul T, de Godoy MRC, Swanson KS. Nutrient digestibility and fecal characteristics, microbiota, and metabolites in dogs fed human-grade foods. J Anim Sci. 2021;99(2). doi:10.1093/jas/skab028
13. Tanprasertsuk J, Perry LM, Tate DE, Honaker RW, Shmalberg J. Apparent total tract nutrient digestibility and metabolizable energy estimation in commercial fresh and extruded dry kibble dog foods. Transl Anim Sci. 2021;5(3). doi:10.1093/tas/txab071
14. Buff PR, Carter RA, Bauer JE, Kersey JH. Natural pet food: A review of natural diets and their impact on canine and feline physiology. J Anim Sci. 2014;92(9):3781-3791. doi:10.2527/jas.2014-7789