Debunking common pet food myths - Veterinary Practice
Your browser is out-of-date!

Update your browser to view this website correctly. Update my browser now



Debunking common pet food myths

Due to the vast array of often contradictory advice, it can be easy for owners and veterinary professionals to be misinformed when trying to select the most appropriate nutritional choices for pets

Like pet owners, clinicians are faced with an ever-growing range of diets, conflicting information on the “best” food available and differing reports on which ingredients to avoid and which provide health benefits to their pets. Inconsistent advice from rating websites, media coverage, social media, internet forums, word of mouth, pet retailers and behaviourists – to name a few – means it can be difficult for caregivers to ascertain whether any of this information is reliable or helpful for their pet.

There is also, unfortunately, a lot of misleading and, in some cases, dangerous advice out there, which further complicates matters and provides challenges to clinicians who have nutritional conversations with caregivers who have read such information. Because of the vast array of advice, it can be easy for both owners and veterinary professionals to be misinformed when trying to select the most appropriate nutritional choices for pets. This article dives into just a few of the many myths about pet food nutrition.

1) Grain-free diets are healthier for cats and dogs

Several arguments have been put forward to promote this concept, including:

  1. Grains are not digestible
  2. They are “cheap fillers” that offer little, if any, nutritional value
  3. They are a common cause of food allergies
  4. Grain-free diets are lower in carbohydrates

a) Pets can digest grains

While uncooked grains are poorly digested by cats and dogs, most properly cooked grains in pet foods are highly digestible. Domestication of pets has led to significant changes to their digestive physiology, which means they have an increased ability to digest starch compared to their wild ancestors (Axelsson et al., 2013). For example, dogs have acquired the AMY2B enzyme, a key enzyme used for starch digestion, and humans have positively selected for this via environmental selection (feeding starches). Dogs and cats can digest carbohydrates from grains with an efficiency greater than 90 percent (de-Oliveira et al., 2008).

b) Grains aren’t “fillers”

FIGURE (1) Commonly used grains in pet foods include wheat, corn or maize, and rice

A “filler” is an ingredient with no nutritional value. Grains such as wheat and corn (Figure 1) contain 75 to 85 percent carbohydrates; these are primarily complex carbohydrates which are digested more slowly than simple sugars, helping to provide sustained energy. They also provide fibre, which has roles in digestive health and regulating intestinal transit, and vegetable proteins, to complement meat proteins from animal sources and help provide a complete and balanced diet. Furthermore, grains also contain essential fatty acids, minerals and B vitamins (Lafiandra et al., 2014) – so they offer a great deal of nutritional benefits!

From a cost perspective, grains are generally lower cost to source than animal-based ingredients, but this reduces the cost of pet food for the pet owner, so cannot be classified as a disadvantage.

c) Grains are not a common cause of skin allergies

Contrary to common owner misconceptions, grains are not a common cause of skin allergies. Food allergies account for a significantly smaller proportion of allergic skin diseases than fleas or environmental allergies. A study by Mueller et al. (2016) found the top three canine food allergens to be proteins from beef, dairy and chicken. Wheat was identified as the fourth most common allergen, accounting for approximately 13 percent of adverse food reactions. The most commonly reported food allergens in cats were beef, chicken and fish.

In some cases, storage mites (SM) may be a confounding factor in patients that show an improvement in skin or gastrointestinal signs after moving from a diet containing grains to a grain-free diet. Storage mites are known to grow on cereal-rich foods, including diets containing grains, and have been shown to exacerbate clinical signs of allergy in dogs sensitised to house dust mites (HDM). Consequently, atopic dogs with high levels of HDM-specific IgE are likely to have a flare of signs after eating foods contaminated with SM, which will likely improve after moving to a diet not contaminated with SM (Olivry and Mueller, 2019). This can lead to a false-positive diagnosis of a food allergy.

d) Grain-free diets are not always lower in carbohydrates

Other perceived benefits of grain-free diets include being lower in carbohydrates, which means they could be healthier for pets and of higher quality. But grain-free is not synonymous with carbohydrate-free; usually, alternative carbohydrate sources, such as peas, sweet potato or cassava, will have been incorporated into the diet. The only way of evaluating whether a product is low in carbohydrates is by studying the label, where carbohydrate content can be calculated based on the declared nutritional analysis (as carbohydrate levels are not stated directly), rather than looking for the presence or absence of grains.

There are also no evidence-based health benefits of a low dietary carbohydrate content except in a small subset of pets, including cats diagnosed with diabetes mellitus.


There is no evidence to substantiate the misconception that grain-free diets are “healthier” for most pets. However, over recent years, a potential link between the feeding of grain-free diets and the development of dilated cardiomyopathy (DCM) in atypical dog breeds has emerged in the United States. Investigations are ongoing, but most diets associated with the reports of non-hereditary DCM have non-soy legumes and pulses (eg peas and/or lentils) high in their ingredient lists. However, while an association has been identified, causation has yet to be identified. Excluding grains will not increase the quality or digestibility of a diet. The only way of establishing the quality and digestibility of a product is to contact the manufacturer, but the packaging or exclusion of grains will give no indicators.

The only way of establishing the quality and digestibility of a product is to contact the manufacturer, but the packaging or exclusion of grains will give no indicators

2) Animal by-products are poor-quality ingredients

Animal by-products are all potentially edible parts of an animal not intended for or in excess of what is required for human consumption. Examples include internal organs, such as the liver and kidneys, which are often viewed as culturally unpalatable and are, therefore, excess to demand in the human food chain. The composition of by-products can vary in different parts of the world, as animal parts consumed in some cultures may not be eaten in other parts of the world.

By-products are strictly regulated. To be permitted in pet food, they must come from animals deemed fit for human consumption and slaughtered under veterinary supervision. Inedible animal parts, such as hooves, are not permitted.

By-products add nutritional value

By-products can offer high nutritional value. Skeletal muscle is deficient in some nutrients, including calcium and other vitamins and minerals. Many of these nutrients are abundant in by-products from poultry, beef, pork, lamb and fish. For example, the liver and kidneys contain 5 to 10 times more riboflavin (vitamin B12) than lean muscle meat and higher levels of omega-3 fatty acids. By-products can also be an excellent source of protein and amino acids.

By-products are more sustainable

In addition to offering nutritional benefits, the use of products surplus to the human food chain by the pet food industry helps to increase sustainability. It is estimated that 25 million tons of raw by-products are produced by the USA alone every year (Meeker and Meisinger, 2015), and their use in pet foods means these parts of the slaughtered animal are not wasted, while also providing a good source of nutrition. It also helps to reduce competition with the human food chain and lowers the cost of production. Without the use of by-products, many owners would not be able to afford to feed their pets a complete and balanced diet.

Without the use of by-products, many owners would not be able to afford to feed their pets a complete and balanced diet

3) “Meat and animal derivatives” suggests poor quality ingredients

When reviewing the composition list of any pet food, ingredients are listed in descending order by weight (heaviest first). In any composition list, ingredients are listed either by general category terms, such as “meat and animal derivatives” and “cereals”, or individually, such as “chicken”, “beef” and “rice”. Products with ingredients listed individually are described as “fixed” formulas in which the same ingredients are used in the same quantities in every batch. Where the composition is listed by category, an “open” formula, where ingredients are flexible between batches, is indicated.

By allowing variation between batches, open formulas can help reduce production costs, resulting in lower product prices compared to fixed formulas. However, fixed formulas provide greater ingredient transparency to consumers and offer more consistent palatability. They are also a more appropriate choice for pets with dietary digestive or skin sensitivities. Fixed formulas are not necessarily superior or higher quality compared to open formulas, but the appropriateness of feeding any fixed or open formula to an individual pet should be considered. For further information on labelling, readers (and clients) are directed to the UK Pet Food website, which has a helpful downloadable factsheet on understanding labelling.

Furthermore, “meat and animal derivatives” is, in fact, a legal category declaration, and provides no indicator of quality. It can incorporate animals of different but unspecified species, though these must all be recognised as being commonly eaten by humans.

Fixed formulas are not necessarily superior or higher quality compared to open formulas, but the appropriateness of feeding any fixed or open formula to an individual pet should be considered

4) Products labelled “natural” or “hypoallergenic” are healthier diet choices

While most pet food labelling is closely regulated, most marketing claims have little regulation and are open to interpretation. Some examples of these claims include:

  1. “Hypoallergenic”: as a general term, this has no meaning as an individual’s sensitivity to ingredients depends on their exposure, so different pets may be sensitive to different ingredients. In scientific terms, “hypoallergenic” food contains only proteins that are hydrolysed to below the molecular weight of common food allergens so the body can no longer recognise them. However, most products claiming to be hypoallergenic will still contain multiple whole proteins – including chicken and beef, which are, as previously mentioned, some of the most common food allergens!
  2. “Holistic”: this is another marketing term positively perceived by pet owners, which is functionally meaningless
  3. “Human-grade”: this term is very ambiguous, particularly as (as previously mentioned) all animal by-products incorporated into pet foods must come from animals certified as fit for human consumption. It is, however, another term that appeals to many pet owners
  4. “Premium”: this is an unlegislated term and gives no indication of the food or ingredient quality
  5. “Natural”: an ingredient declared to be “natural” must meet the definition laid out by FEDIAF (the voice of the European Pet Food Industry, which lays out standards and guidelines for pet foods). Ultimately, this boils down to all ingredients being subjected only to physical processing to maintain their natural composition as much as possible. For example, an ingredient can be dried to make it more amenable to processing, but adding antioxidants or preservatives excludes it from being “natural”. In comparison, pet food can be described as natural, or use this term on the packaging, without needing to follow any legislation or even contain any natural ingredients! Packaging colour and imagery can be used to give the impression of a “natural” product, but this is not regulated at all

5) Home-made diets are healthier and provide better nutrition than commercial diets

Home-prepared diets have grown in popularity over recent years. For some pet owners, this is a response to concerns about the quality of commercial diets; for others, feeding home-prepared foods reinforces the human–animal bond. A further subset requires a home-prepared diet to manage a medical condition.

Proponents of home-prepared foods claim they are a safe and natural way to feed animals. It is true that fresh meat – whether raw or cooked – is palatable to most dogs and cats, can be highly digestible and, depending on the cut selected, may be higher in protein and fat than many dry kibble diets (potentially resulting in a pet that enthusiastically eats their food, and may have a low stool volume and shiny coat). However, these positive aspects provide no proof that home-made diets are superior to commercial foods and omit the potential negative consequences.

Ensuring a balanced diet is difficult

Providing a nutritionally balanced home-made diet is not impossible, but it is very challenging. There are 37 essential nutrients for dogs and over 40 essential nutrients for cats, all of which must be incorporated at the appropriate levels within their diet. Calorie control can be difficult, and there is a risk of recipe drift, even when balanced by a board-certified veterinary nutritionist.

There are 37 essential nutrients for dogs and over 40 essential nutrients for cats, all of which must be incorporated at the appropriate levels within their diet

Many recipes are available online and in magazines, but none have actually been tested and established as balanced. In some cases, they could pose toxicity risks due to the inclusion of ingredients such as onions and garlic. Published reviews of the nutritional adequacy of home-prepared recipes have found very few of these recipes that provide a complete and balanced source of nutrients. One study found that 113 of 114 home-prepared recipes for cats had vague preparation instructions, 46 contained no feeding directions and 20 did not provide enough information for nutritional analysis. Not a single recipe met all recommended nutrient levels for cats (Wilson et al., 2019). In another study, 95 percent of the 200 recipes for home-prepared dog foods (64 percent of which had been written by veterinarians) were deficient in at least one essential nutrient and 84 percent lacked multiple required nutrients (Stockman et al., 2013).

Consistent deficiencies found in many home-prepared recipes are sufficient sources of calcium and trace minerals (such as iodine, selenium, copper and zinc), linoleic acid and essential fat- and water-soluble vitamins.

While the perceived benefits of home-prepared diets may be reinforced daily to the caregiver, nutrient deficiencies are insidious in onset and can lead to long-term complications, including poor skin and coat health, chronic diarrhoea and anaemia, depending on the specific nutrient deficiencies. Unless formulated by a board-certified nutritionist, home-made diets are extremely likely to be unbalanced and may pose long-term health risks.

While the perceived benefits of home-prepared diets may be reinforced daily to the caregiver, nutrient deficiencies are insidious in onset and can lead to long-term complications

Commercial diets are complete

In comparison, commercial diets must be labelled either “complete” or “complementary”, which means they must be mixed with other foods to fulfil the pet’s nutritional requirements. “Complete” diets are formulated to meet FEDIAF nutritional guidelines and contain all macro- and micronutrients at appropriate levels required to support health according to the latest scientific guidelines.

So how can caregivers trust that the diet is truly complete and balanced? There is close regulation of the pet food industry in Europe, and all diets must demonstrate they are “complete” with computer formulation. Some brands also do additional testing, including chemical analysis of the diet (measuring specific nutrients to check, for example, that what claims to be in the diet is actually present) and feeding trials. Feeding trials are generally only conducted by larger food manufacturers as they are costly and take time, but they can be very valuable. These trials look at feeding the diet to healthy animals to demonstrate nutritional adequacy and assess factors such as digestibility and faecal quality. They also help to identify potential interactions between nutrients that would not be evident from computer formulation alone.

Awareness of the fact that very few of the smaller pet food companies and most raw diet companies have not conducted any feeding trials with their diets is important. Although some pet owners distrust large corporate companies, these companies have generally invested a large amount of money in research behind their pet food and in maximising the safety and nutritional adequacy of the diets they produce. They are also less likely to outsource their sourcing and manufacturing, enabling them to keep tight quality and safety control throughout the production process.

Further information for vets and their clients: where should I go to learn more?

Veterinary practices must identify themselves as credible, trustworthy and confident sources of advice that can direct clients to reliable sources of information. The author recommends the UK Pet Food and World Small Animal Veterinary Association (WSAVA) websites as particularly excellent sources of reliable, unbiased and easy-to-understand information for clinicians and owners alike. Veterinary practices can also direct clients to these websites and/or use the tools they offer, including helpful downloadable fact sheets.

Caregivers should be advised against rating websites as they often rank pet foods based on their own opinion, including bias against manufacturing companies and whether the ingredients the author perceives to be “good” or “bad” are included in the diet rather than considering factors such as evidence base and quality control. These websites can, unfortunately, be very misleading and are not a credible source of information. Some pet food manufacturers’ websites can also be helpful, offering useful advice, diet information and, for veterinary professionals, opportunities for continued professional development.

For further information on the content discussed in this article and a range of other myth-busting resources, including raw feeding, the author has recorded some podcasts appropriate for both veterinary professionals and caregivers (available by searching for “Purina Bitesized Nutrition” on Spotify or Libsyn).

Have you heard about our
IVP Membership?

A wide range of veterinary CPD and resources by leading veterinary professionals.

Stress-free CPD tracking and certification, you’ll wonder how you coped without it.

Discover more