The pet food myths owners believe most, ranked against the evidence

A pet food myth is a widely held belief about what dogs and cats should eat that survives despite contradicting the available veterinary and regulatory evidence. The striking pattern in our reference work is that the myths owners hold most confidently are often the ones the evidence contradicts most cleanly. This article takes five of the most repeated beliefs we see in owner questions and places each one next to what bodies such as the FDA, AAFCO, FEDIAF and the WSAVA actually report. The aim is not to scold anyone: most of these ideas are intuitive, repeated by people acting in good faith, and reinforced by packaging. The aim is to show where intuition and evidence part company. A quick orientation before the list. The World Small Animal Veterinary Association, the body whose nutrition guidelines anchor much of this field, federates about 113 member associations representing more than 390,000 veterinarians (WSAVA, 2021). When that consensus and a popular belief disagree, the belief is the thing worth re-examining.

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Myth one: grains are cheap fillers that pets cannot digest

This is perhaps the most commercially successful myth in the category, because it sells a solution. The evidence runs the other way. Dogs are not wolves with a marketing problem: during domestication the dog evolved markedly better starch digestion, carrying several copies of the amylase gene that are nearly absent in the wolf (Axelsson et al., 2013). Cooked grains are digested efficiently, and a concentrate such as corn gluten is roughly 60 percent protein and well digested once cooked (FEDIAF, 2024).

The "filler" framing also misreads what grains do in a recipe. They contribute digestible energy, fibre and micronutrients, not empty bulk. The one situation where avoiding a specific grain is justified is a diagnosed food allergy, and even then grains are rarely the culprit, as the next myth shows.

Myth two: food allergies are common, and grains cause most of them

Owners reach for "allergy" quickly, usually pointing at grain. Two figures reframe the whole topic. First, food allergy accounts for only about 1 percent of all skin diseases in dogs and fewer than 10 percent of canine skin allergies (MSD Veterinary Manual, 2023). Most itching is not dietary at all. Second, when a true food allergy does exist, the leading triggers are animal proteins, not cereals: beef accounts for about 34 percent of canine cases and chicken about 15 percent, with wheat fourth at roughly 13 percent (Mueller et al., 2016).

So the popular pairing, common plus grain-driven, is doubly wrong. Allergy is uncommon, and when present it more often traces to the meat than to the grain. You can see why a grain-free recipe built around chicken would do nothing for a chicken-allergic dog.

Myth three: animal by-products are low-grade waste

The word "by-product" sounds like a euphemism for rubbish, so the belief that by-products are dangerous or worthless is intuitive. In regulatory and nutritional terms it is mistaken. By-products are simply the parts of an animal not typically eaten by people in a given market, such as liver, lung, spleen and kidney. Many are nutrient-dense organ tissues, often richer in certain vitamins and minerals than muscle meat. The legitimate concern is sourcing and quality control, which is a question about the maker, not about the category.

Myth four: high protein damages the kidneys

This belief is so entrenched that owners often cut protein in healthy ageing pets to "protect" the kidneys, which can quietly erode muscle. The protein-kidney link is not supported in healthy animals. In existing chronic kidney disease, the nutrient that matters for slowing progression is phosphorus, not protein as such, and renal diets are built around phosphorus restriction while keeping protein adequate to preserve body condition. Reducing a maintenance food across the board lowers protein and micronutrients in proportion and can erode muscle mass (AAHA, 2021). Protein is the variable owners cut; phosphorus is the variable that matters.

Myth five: a positive blood or saliva test confirms a food allergy

Quick allergy panels are widely sold and widely trusted. They do not work as a diagnosis. A study in the JAVMA found that serum and salivary antibody tests returned positive results in dogs with no clinical signs of allergy whatsoever (Lam et al., 2019), and other work has shown such panels flagging "allergens" from sham samples containing no biological material at all. A positive result does not confirm allergy and a negative one does not rule it out. The diagnostic reference remains a strict elimination diet supervised by a vet.

Three more beliefs that nearly made the list

The top five are the most confidently held, but three runners-up are common enough to address briefly, because each follows the same intuition-over-evidence pattern.

Raw is more natural and therefore healthier. The appeal is obvious, yet the reference review by Freeman and colleagues found the claimed benefits of raw feeding largely unproven by controlled trials (JAVMA, 2013), and the WSAVA states there is no documented evidence of a health benefit while the risks, including pathogen exposure, are well established (WSAVA, 2021). A well-formulated premium kibble reaches the same nutritional targets (Tufts Petfoodology, 2025).

Homemade is healthier than commercial food. The largest assessment of home recipes found 95 percent deficient in at least one essential nutrient, including recipes written by general-practice vets (UC Davis, 2013). Fresh ingredients do not equal a balanced ration.

Crude ash is a sign of poor quality. Ash is not an added filler but an analytical measurement, the non-combustible mineral fraction left after laboratory calcination (FEDIAF, 2024). A higher figure in a meat-rich food usually reflects the natural mineral load of bone, which raises a calcium-to-phosphorus question rather than a quality one (NRC, 2006).

Why "by-product" deserves a second look

It is worth dwelling on the by-product myth, because it is where the gap between word and substance is widest. Offal ranks among the most nutrient-dense components of a ration: liver concentrates vitamin A, haem iron, copper, zinc and B-group vitamins at levels above lean muscle, and heart is a muscle rich in taurine, which is essential for the cat (FEDIAF, 2024). The NRC recognises both, noting that the documented risk of hypervitaminosis A from excess liver actually confirms how concentrated these organs are, rather than how poor (NRC, 2006). The legitimate concern is opacity, not nutrition: a generic meal with no species named can mix heterogeneous origins from batch to batch, which complicates traceability (FEDIAF, 2024). That is a transparency issue to raise with the maker, not a reason to fear the category. The distrust, the reference material is blunt about, stems mainly from the cultural connotation of the word (FEDIAF, 2024).

The five myths at a glance

Why these myths persist

Three forces keep them alive. Packaging rewards simple stories, and "no nasty grains" fits on a bag better than a paragraph about amylase genes. Anecdote is persuasive: an owner who switches food and sees less itching credits the new recipe, even though seasonal allergens or coincidence may explain the change. And quick tests give a number, which feels like an answer even when the number means nothing clinically. Recognising the mechanics of a myth is the first defence against the next one.

There is also a deeper reason these particular myths endure: they each contain a grain of truth that has been over-generalised. Grains genuinely are problematic for the rare grain-allergic dog, so "grains can be a problem" mutates into "grains are bad for all dogs". By-products genuinely can be opaque to trace, so "some by-products are poorly documented" becomes "by-products are waste". Protein genuinely does need managing in advanced kidney disease, so "restrict phosphorus in diagnosed renal patients" collapses into "protein is bad for kidneys". The myth is usually a true statement that has lost its conditions. Restoring the conditions, who, when and how much, is what turns a scary slogan back into a manageable fact.

Alt text: "Five-row comparison panel pairing each common pet food belief with the matching scientific or regulatory evidence."

How to stress-test a claim yourself

You do not need a nutrition degree to filter most myths. Three questions do a lot of work. Does a primary body such as the FDA, AAFCO, FEDIAF or the WSAVA say the same thing, or only a brand? Is the claim about a whole category, such as "grains" or "by-products", when quality actually varies maker by maker? And does the claim sell something convenient, such as a test or a premium line? Claims that fail all three deserve scepticism.

For the deeper dives, our reference library separates the controversy from the chemistry. The questions on whether by-products and common additives are dangerous are handled in detail in our controversial ingredients FAQ, and the diagnostic reality of allergies is covered in the allergies and intolerances FAQ. If you want a structured way to weigh a food rather than a slogan, the choosing quality pet food guide walks through the checkable signals, and the food allergy elimination diet guide explains the only method that actually confirms a dietary trigger. The recurring technical idea under several of these myths is whether a food is complete and balanced, a defined regulatory status rather than a marketing adjective.

The takeaway (food myths)

The myths owners believe most are not random. They cluster around stories that are easy to sell, easy to confirm with anecdote, and flattering to act on. The evidence is less tidy: grains are fine for most pets, allergies are uncommon and usually meat-driven, by-products are a sourcing question, protein is not the kidney villain, and quick allergy tests do not diagnose anything. None of this requires fear. It requires the habit of checking the popular claim against the body of evidence, and trusting the second one when they disagree.