Twelve pet food myths checked against the evidence

The front of a pet food bag is marketing, and several of the most repeated rules about feeding dogs and cats come from that marketing rather than from research. The World Small Animal Veterinary Association's nutrition committee puts it plainly: unregulated terms such as "premium" are of little practical value for judging a food. Below are twelve common beliefs, each checked against the evidence and the labeling rules.

1. Grain-free is not healthier by default

No research shows that grain-free food is healthier for dogs that do not have a diagnosed reaction to a grain. Cooked rice, oats, barley and corn are digestible and supply energy, fiber and some vitamins and minerals.

Grain-free diets also carry an unresolved question. Since 2018 the FDA has investigated reports of dilated cardiomyopathy (DCM), a disease of the heart muscle, in dogs without a known genetic cause. By November 2022 it had received 1,382 reports. Most of the diets involved listed peas, lentils or other pulses high in their ingredients, and these included both grain-free and grain-containing foods. The FDA describes non-hereditary DCM as a complex condition that may involve genetics, other illness and diet, and it has not named a single cause. It advises talking to a vet before changing a dog's diet.

2. Dogs are not wolves

Dogs changed during domestication, and diet was part of it. A whole-genome comparison of dogs and wolves in Nature found signs of selection in ten genes involved in starch digestion and fat metabolism, with evidence of better starch digestion in dogs than in wolves. The authors concluded that adapting to a starch-rich diet was an early step in domestication. A dog is still a carnivore in its anatomy, but it is not a wolf, and copying a wild diet ignores that history.

3. By-products include organ meat

By-products are defined ingredients, not floor sweepings. AAFCO describes meat by-products as the parts of slaughtered animals that are not normally used for human food, including internal organs. Liver, heart and kidney are nutrient-dense. The objection to by-products is mostly about how they sound, and AAFCO notes that it does not regulate those aesthetic opinions. A label that names the species ("chicken by-products") tells an owner more than a generic term does.

4. Raw food carries a measurable infection risk

Raw diets are popular, but evidence for their claimed benefits is limited, while the infection risk has been measured. When FDA laboratories tested pet foods, 15 of 196 raw pet food samples carried Salmonella and 32 carried Listeria monocytogenes. The dry dog food samples tested carried neither, and only one of the dry cat food samples tested positive for Salmonella. These bacteria can make pets ill and can spread to the people who handle the food or share the home. The FDA's raw pet food guidance includes handling advice for owners who feed raw anyway. Home-made raw diets add the risk of an unbalanced recipe.

5. Corn is not a filler

"Filler" implies no nutritional value, and that does not fit corn. Ground and cooked, it is a digestible source of carbohydrate, the essential fatty acid linoleic acid and fiber. Corn is not a complete protein source and should not be the backbone of a diet, but its presence in a complete and balanced food is not a sign of low quality.

6. The first ingredient says little about quality

Under AAFCO labeling rules, ingredients must be listed in descending order by weight. Fresh meat is mostly water, so fresh chicken listed first may add less protein to the finished dry food than chicken meal listed second. The order can also mislead the other way. Several forms of one ingredient, such as peas, pea protein and pea fiber, can each sit below the meat while together outweighing the meat. The list also says nothing about the quality of each ingredient. The guaranteed analysis, the calorie content and the nutritional adequacy statement tell an owner more.

7. Marketing words are not quality standards

"Premium" and several similar marketing words have no regulatory definition. "Natural" does have one under AAFCO: roughly, ingredients from plant, animal or mined sources that have not been produced by a chemically synthetic process, with exceptions such as added vitamins and minerals. AAFCO is explicit that nothing in that definition means natural ingredients are safer than synthetic ones. A natural claim describes processing, not nutrition.

8. Home-made recipes are rarely complete

Home-made diets can work, but recipes from books and websites rarely provide everything a dog or cat needs. When researchers prepared and chemically analyzed 100 published home-made recipes for dogs and cats, none supplied recommended levels of every nutrient measured, and more than 84% fell short on three or more. Calcium and potassium were the most common shortfalls in dog recipes, iron and zinc in cat recipes. A balanced home-made diet needs a recipe from a board-certified veterinary nutritionist, with the specified supplements used every time.

9. Carbohydrates are not the problem

Dogs digest cooked starch well, as the genetic evidence above suggests, and carbohydrates supply energy and fiber in many good diets. Cats are obligate carnivores and need more protein than dogs, so a cat food built mainly on starch is a poor fit. That still does not make carbohydrate the cause of obesity in either species. Weight gain comes from eating more energy than the animal uses, whether the calories come from fat, protein or starch.

10. Rotating proteins has little evidence behind it

Rotating protein sources is harmless for most animals if each change is gradual, but there is little evidence that it brings health benefits or prevents food allergies. One practical drawback is worth knowing. Diagnosing a food allergy relies on an elimination diet using a protein the animal has never eaten, or a hydrolyzed diet, and a dog or cat that has eaten a long list of proteins leaves fewer novel options.

11. Price is a poor guide to quality

Price and quality do not reliably go together. The WSAVA guidelines on selecting pet foods do not mention price. They suggest judging a brand by these questions:

• Does the company employ a qualified nutritionist, with a PhD in animal nutrition or board certification in veterinary nutrition?
• Who formulates the diets, and with what training?
• What quality control covers ingredients and finished products?
• Has the company done product research, and is it published in peer-reviewed journals?
• Can the company give a typical analysis of all essential nutrients and the calorie content on request?

The same guidelines advise caution with any brand that cannot or will not answer.

12. Pets do not choose food for its nutrients

Dogs and cats choose food by smell, taste and texture. A dog will eat chocolate, grapes and the contents of a bin, none of which it needs. A cat can become fixated on one flavor or type of food and refuse a complete diet. Palatability and nutritional adequacy are separate qualities. A food that a pet eats eagerly still needs a complete and balanced statement for its life stage, and the animal's weight, body condition, coat and stools are better guides than its enthusiasm.

Sources

1. Guidelines on selecting pet foods. WSAVA Global Nutrition Committee, 2021.
2. Questions and answers: FDA's work on potential causes of non-hereditary DCM in dogs. U.S. Food and Drug Administration.
3. The genomic signature of dog domestication reveals adaptation to a starch-rich diet. Nature, 2013.
4. Byproducts. Association of American Feed Control Officials.
5. Get the facts: raw pet food diets can be dangerous to you and your pet. U.S. Food and Drug Administration.
6. Reading labels. Association of American Feed Control Officials.
7. Natural. Association of American Feed Control Officials.
8. Concentrations of macronutrients, minerals and heavy metals in home-prepared diets for adult dogs and cats. Scientific Reports, 2019.