I have often discussed the problems with homemade pet diets, which are frequently recommended in books and websites that complain about commercial food or proclaim some magic method for preventing or curing disease. Raw diets, grain free diets, and other fads often involve making pet food at home from recipes from self-proclaimed experts in nutrition, though there are also commercial versions of each fad available not long after it takes hold. Of course, the only real experts in pet nutrition are those board certified by the American College of Veterinary Nutrition. And while there is ample evidence that homemade diets are often nutritionally inadequate, (e.g. 1, 2) most of the scary claims about commercial diets are just myths and misconceptions.
A recent study has reinforced these already well-established points.
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 Dec 1;241(11):1453-60. doi: 10.2460/javma.241.11.1453.
This study looked at recipes from books and web sites that recommended diets for dogs with cancer, as well as commercial diets marketed for use in canine cancer patients, and evaluated the nutritional adequacy of the diets based on established AAFCO or NRC guidelines. The findings were quite clear, and the recommendations consistent with those veterinary nutritionists have been making for some time.
Published recipes of home-prepared diets for pets with various health conditions are rarely nutritionally adequate. None of the 27 recipes identified and evaluated met NRC RA or AAFCO nutrient profiles for all essential nutrients. In some cases, the recipes contained excessive, potentially toxic amounts of nutrients.
Recipes formulated or provided by veterinarians were not more nutritionally sound than were recipes formulated or provided by nonveterinarians.
Only 2 of 39 (5.1%) commercial diets had passed AAFCO feeding trials (one for adult maintenance and the other for all life stages). The majority (35/39 [89.7%]) of the diets were formulated to meet AAFCO nutrient profiles for all life stages (27 diets) or adult maintenance (8 diets
There is a paucity of experimental data that support specific nutrient profiles or ingredients for dogs with cancer. Dogs with cancer do not have higher or lower requirements for protein, fat, calories, or any other specific nutrients, compared with requirements for healthy dogs. Therefore, it is of concern that none of the recipes for home-prepared diets met NRC RA or AAFCO nutrient profiles for adult maintenance in dogs… All of these inadequate diets have the potential to cause nutritional disease at a time when nutrition should be optimized to provide maximum metabolic support and immune system function and to help decrease adverse effects attributable to cancer treatments.
Commercial diets and recipes of home-prepared diets reflected the current popularity of grain-free diets. No data support health benefits of non-grain sources of carbohydrate over carbohydrates provided by grains; however, many manufacturers still tout the nutritional superiority of grain-free products.
Grain-free diets are often marketed as lower in carbohydrate content, but this is not a consistent finding. Approximately one-third of the recipes of grain-free home-prepared diets and commercial diets did not meet the defined criteria for low-carbohydrate diets.
Low-carbohydrate diets are commonly recommended for dogs with cancer on the basis that many cancer cells use aerobic glycolysis and fermentation of pyruvate to lactate as a main source of energy… it is theorized that feeding a low-carbohydrate diet could effectively starve cancer cells through a decrease in the supply of glucose. However, despite the fact that this theory has been in existence for nearly a century, minimal data have been published to support the tangible benefits of low-carbohydrate diets for any species of animal with cancer. To our knowledge, there are no published data to support the contention that low-carbohydrate diets are of clinical benefit with regard to tumor growth, disease-free interval, or survival time in dogs, and further studies are required before appropriate recommendations can be made.
The number of recommendations for feeding raw meat diets to cancer patients is a concern because contamination with pathological bacteria has been reported for raw meat for human consumption and for commercial raw diets. Cancer patients, even those not receiving chemotherapy, likely have some degree of altered immunoregulation, and many dogs receiving chemotherapy are clinically immunosuppressed, which dramatically increases the risk of illness or even death from contaminated food sources. In humans, the risk of illness attributable to foodborne bacteria in cancer patients is such a concern that patients receiving chemotherapy are commonly advised to eat raw fruits and vegetables only when at home.
It is possible that feeding a diet that does not meet AAFCO recommendations or NRC RAs for various nutrients may not cause overt clinical disease. Although some nutrient deficiencies (eg, thiamine or taurine) can be evident in adult animals after a food deficient in those nutrients is fed for weeks to months, it can be months to years before clinical signs are evident for other nutrient deficiencies (eg, calcium in an adult animal). The status of many nutrients is not easily determined, and the first clinical signs of deficiency may be catastrophic (calcium deficiency resulting in osteopenia and pathological fractures or taurine deficiency resulting in dilated cardiomyopathy).
Currently, the authors are aware of no evidence to suggest that cancer patients have nutrient needs that differ dramatically from maintenance requirements. Many dog owners change to home-prepared diets because of an overall perception that they are healthier than commercial diets, rather than because they provide specific nutrient profiles. Thus, it appears appropriate that home-prepared diets be formulated to meet nutrient guidelines similar to those of commercial products.
Homemade diet recipes are almost always nutritionally inadequate, even if formulated by a veterinarian (unless they are a board-certified nutritionist)
There is no evidence for benefits from current nutritional fads such as raw or grain-free diets, but there is the potential for harm from these diets.
Commercial diets are consistently more appropriate nutritionally than homemade diets.
There is little evidence to support the idea that cancer patients should be fed a different diet from healthy dogs (with the possible exception of extra fatty acid supplementation).