30 Harmful Cat Food Ingredients to Avoid

In the last couple of decades, a lot has been done to raise consumer awareness about the ingredients in commercial pet food. Checking product labels can help you spot cat food ingredients to avoid, but you need to know what to look for.

We’ve gathered a list of 30 harmful ingredients commonly found in cat food to help you make the healthiest choice when buying cat food for your feline family member.

The importance of reading labels

People read pet food labels to make sure they’re buying the right product for their pets. And while checking the product’s list of ingredients isn’t the only way to learn more about the cat food your buying, it’s still a good start.

In addition to what ingredients are in your cat’s food, it’s important to know where the ingredients are sourced, and where it’s manufactured, because not all countries have the same pet food regulations.

Also, a pet food company needs to be transparent – unwillingness to disclose any information about their product or practices may be a red flag.

Before we dive in, please note that the following ingredients mentioned aren’t harmful to cats by default. However, there have been cases in which excessive exposure to these ingredients had negative effects on the cats’ health. If you’re unsure about the quality of a certain product, this list can help you decide.


Preservatives are added to food to keep it fresh for a longer period, but not all of them are healthy. Cheaper, chemical preservatives have no nutritional value and can be harmful to your cat’s health.


BHA or butylated hydroxyanisole is a chemical preservative that’s efficient in prolonging the freshness of dry food, but it’s considered a human carcinogen, according to The National Toxicology Program of the Department of Health and Human Services.

Although it’s labeled safe in low doses, experiments with lab animals have shown that BHA causes benign and malignant tumors. So why take the risk? Instead, buy cat food that uses safe preservatives, like vitamin C or vitamin E.


BHT or butylated hydroxytoluene is structurally similar to BHA and they’re often used together as food preservatives. BHT is usually added to oils and fats. Although it’s not listed as a carcinogen and deemed safe in the amounts found in processed food, some data has shown that BHT indeed causes cancer in animals.

Experiments with lab rats have shown that BHT causes lung and liver tumors, as well as thyroid changes.


Ethoxyquin is a synthetic antioxidant that’s sometimes used in pet food to prevent fats from becoming rancid. It’s registered as a pesticide. It’s banned from use in human consumption, except in certain seasonings, like chili and paprika, where it’s used for color preservation.

When it comes to ethoxyquin’s impact on animal health, the data is inconclusive, but there are reasons for concern. Some experiments have shown the negative effects of this substance on the liver and kidneys, and there’s also a potential risk of ethoxyquin causing genetic mutations.

The inability to fully assess the safety of ethoxyquin because of lack of data led to the European Union formally suspending the use of this preservative in animal feed.

cat food ingredients to avoid meat by products

Meat by-products

Meat by-products are defined by AAFCO as “the non-rendered, clean parts, other than meat, derived from slaughtered mammals.” They can include the brain, lungs, kidneys, spleen, blood, bone-in other words, the majority of animal parts other than the muscle tissue.

Some by-products are fit for human consumption, while others are not, but they can be perfectly safe and nutritious for animals, according to the AAFCO. However, since by-products can contain almost any type of animal matter, including matter from sick and euthanized animals, together with drugs used to kill them, they are considered a low-quality protein source.

Also, since it’s not specified what animal species is in question, you don’t know what’s in it, which isn’t reassuring.

Meat and bone meal

The AAFCO defines meat and bone meal as “the rendered product from mammal tissues, including bone, exclusive of any added blood, hair, hoof, horn, hide trimmings, manure, stomach and rumen contents except in such amounts as may occur unavoidably in good processing practices.”

Meat and bone meal is obtained by the process of rendering, which involves removing fat and water from animal tissue and leaving primarily protein and minerals. And although the result is a highly-concentrated product with high levels of protein, the quality of that protein may in certain circumstances be questionable. If you’re looking for high-protein cat food options check out our article on “The Best High Protein Cat Foods.”

Rendering also involves cooking the product to get rid of harmful bacteria, but during the process, you also get rid of natural enzymes, which contributes to the lower-quality protein you get in the end.

Low-grade fats

Fats are necessary for a cat’s diet and they are the main energy source for felines. Fats have numerous roles in a cat’s body, including transporting nutrients between cells, enhancing the absorption of fat-soluble vitamins A, D, E, and K. Plus fats protect cells from bacterial and viral infections.

Fats can enhance the taste and texture of cat food, making it more palatable for cats. The minimum amount of fat content in cat food should be around 9% of dry matter.

Common sources of fat in cat food are animal fat and vegetable oil, but it’s important to pay attention to the quality of these sources. It’s best to look for a named source of fat, such as chicken fat, rather than non-specific terms like “animal fat”, which comes from the process of rendering low-quality protein sources.

For healthy cat food that is high in calories, we did a deep dive into “The Best High-Calorie Cat Food.”

Beef tallow

Beef tallow is the fat extracted from rendered beef, and by law, tallow intended for use in human food, pet food, and animal feed must not be derived from chemically euthanized animals. However, not every pet food manufacturer complies with these rules.

In 2018, several Gravy Train canned dog foods were contaminated with pentobarbital, a drug used as a sedative in treating insomnia, which can have lethal consequences if ingested by pets. Pentobarbital came from beef tallow, which was derived from chemically euthanized animals.

Safflower oil

Safflower oil is derived from the seeds of the safflower plant. It’s often found in cat food because it contains linoleic acid, a type of omega-6 fatty acids which cats can’t synthesize on their own.

However, safflower or any other plant-derived oil is of little use to cats, since they can’t thrive on a plant-based diet.

Flax oil

Flax oil is derived from flax plant seeds and it contains high levels of alpha-linolenic acid, which is an omega-3 fatty acid with anti-inflammatory properties. Like we mentioned earlier, cats are unable to use nutrients from plants effectively, so flax oil won’t be so productive in felines.

cat food ingredients to avoid carbs

Grains and carbohydrate fillers

Cats don’t have a strong need for carbohydrates in their diet, since their natural prey contains only around three percent carbs. Healthy cats can tolerate diets that contain up to 40 percent carbs, but excessive use of fillers should be avoided since they offer no nutritional value and may cause digestive issues.


According to a study at Tufts University, peas are some of the most common plant-sourced ingredients in grain-free diets. Many pet food brands swapped grains for peas as a more natural alternative, but there is little evidence to show that peas are healthier for cats than grains.

Although a 2008 study showed that cats can efficiently digest the starch from pea-based diets, some other issues are yet to be addressed. Peas are legumes, and legumes contain high levels of phytic acid, which tends to bind calcium, magnesium, and iron in animals and humans.

Also, peas contain lectins, sticky, sugar-binding molecules that act as plants’ natural defense against predators. Their binding ability enables them to attach to the small intestine’s lining and disrupt digestion and nutrient absorption.

Lectins can also attach to leptin receptors which regulate carbohydrates into glucose and disrupt their function, which may lead to obesity and diabetes.


Although there is some evidence to show that cats can digest corn efficiently, meaning that corn has greater bioavailability (digestibility) compared to some other grains, it’s still not as quality source of protein as meat sources are.

According to the FDA, corn is the most commonly grown crop in the United States, and most of it is GMO. In 2018, 92 percent of all planted corn was genetically modified, and these crops haven’t been studied in the long run for their effects on humans or animals.


Wheat and grains, in general, are added to pet food as cost-effective sources of protein, but wheat can’t replace meat as a source of protein. It’s important to remember that cats are obligate carnivores that require animal-based protein to survive, so wheat gluten or any other plant-based protein can never be the only protein source in your cat’s diet.

Many pet owners worry about gluten allergies, although gluten sensitivity in cats is extremely rare.


Soy belongs to legumes, and it’s used in human and pet food as an alternative to animal-based protein. Soy is a less expensive alternative to meat protein, it’s questionable whether it possesses the same quality, and since soy is a plant-based protein. And it can’t be the sole source of protein in your cat’s food.

Like corn, most soy grown in the United States is genetically modified.

cat food ingredients to avoid fiber


Although fiber is associated with health benefits in pets and humans, not all types of fiber are equally beneficial for cats. Quality sources of fiber for cats include beet fiber and rice bran, as they promote the creation of good bacteria, without decreasing digestibility.


Cellulose is the least fermentable type of fiber for cats and it’s the most common type of insoluble fiber found in pet foods. Cellulose may cause the food to pass too quickly through a cat’s digestive tract, without giving enough time for nutrients to be absorbed.

Oat fiber

Oat fiber has similar properties to cellulose. It’s not easily fermentable by cats and it may prevent proper nutrient absorption.

Alfalfa meal

Alfalfa meal contains phytoestrogens, which have been proven to disrupt endogenous hormone levels and the ovulatory cycle in animals. It also contains several poisonous saponins, substances found in plants, including medicagenic acid, which tampers with proper nutrient absorption.


Thickeners are often found in canned cat food.


Carrageenan is a controversial ingredient on both human and pet food labels. It’s an additive that’s used to thicken, emulsify, and preserve foods. It’s made from red seaweed native to the UK.

Research has shown that carrageenan can potentially cause cancer in humans, but it can also cause intestinal lesions, ulcerations, and tumors in animals.

Guar gum

Guar gum has a sticky texture and it’s commonly used in cat food. It has been shown to decrease the level of protein digestibility.

cat food ingredients to avoid guar gum

Menadione, or Vitamin K3

Vitamin K is an important nutrient for animals, and it can be found in leafy greens, liver, meat, milk, and egg yolk. It has three types: Vitamin K1, Vitamin K2, and Vitamin K3. While K1 and K2 occur naturally, K3 is a synthetic, artificial form of this vitamin

Vitamin K3, also known as Menadione or Menadione Sodium Bisulfite or Bisulphate is highly toxic, which caused it to be banned for human consumption in the United States because ingestion could result in allergic reactions, hemolytic anemia, and cytotoxicity in liver cells.


Caramel is an additive used for food coloring and it’s often added to dry and canned food to make them look like real meat. Caramel contains 4-methylimidazole (4-MIE), which is a known animal carcinogen.

Studies have shown that long-term exposure to 4-methylimidazole caused lung cancer in mice, so caramel has been added to California’s list of Chemicals Known to the State to Cause Cancer or Reproductive Toxicity.

worst dry cat food

Food coloring

Cats are less sensitive to changes in color brightness, so they are unable to see vibrant color tones like humans do. Therefore, food coloring is not intended for cats, but their owners. Its only use is to give the product a more desirable appearance.


In the 1970s, there were reports of Red dye 2 being connected to cancer, namely bladder tumors in rats. This led to the FDA banning it from products sold in the United States. Red dye 3 also poses a risk of cancer (experiments showed thyroid tumors in rats), and it was under a partial ban for a short time in the 1990s. Red dye 40 poses a risk of allergic reactions and it is suspected to trigger behavioral problems in children.


Yellow dyes 5 and 6 can cause allergic reactions, while dye 5 causes genotoxicity and hyperactivity in children. Yellow dye 6 has a potential for causing adrenal and testicular tumors in rats.


Blue dye 1 can cause allergic reactions and potentially kidney tumors in mice. Blue dye 2 potentially causes brain and bladder tumors in rats.


Green dye 3 has the potential for causing bladder tumors in rats.


While increased amounts of sodium in pet diets can cause increased urine output and reduce the risk of forming kidney stones. For pets that suffer from renal disease, high amounts of sodium can have a negative effect on kidneys.

Sodium Nitrite

Sodium nitrite is used in cat food for coloring purposes, to achieve a red look, and to keep the food fresh. In 1997 in New Zealand, there were three tragic reports about cats dying from nitrite poisoning.

The death of three cats, from two separate households, was linked to toxic concentrations of sodium nitrite used as a preservative in commercial pet food. Post-mortem examination of the three cats revealed a brownish discoloration of the blood suggestive of nitrite poisoning.

Sodium Tripolyphosphate

Sodium Tripolyphosphate (also known as STPP or E451) is a preservative that helps food retain moisture and stay fresh longer. It’s also added to dental pet food diets to reduce the buildup of calcium.

However, some studies have shown that STPP in pet food causes decreased iron content in bone, liver, and spleen, and bone depletion of calcium.

cat food ingredients to avoid onion

Titanium Dioxide

Titanium dioxide is a potentially carcinogenic artificial color used as a white pigment. Research has shown that ingestion of nanoparticles from titanium dioxide can cause DNA damage, inflammation, and genetic disorders, in addition to cancer in animals.

Iron oxide

Iron oxide is a coloring agent that’s added to food to achieve a red, meaty color. Although there isn’t scientific evidence showing that iron oxide is harmful to cats, it’s still an additive used solely to make food look more appealing. There is no nutritional reason to use it in pet food.

Glyceryl monostearate

Glyceryl monostearate is a chemical additive that’s used to thicken pet food and preserve its freshness. It’s suspected of being an environmental toxin. Experiments with lab animals showed that glyceryl monostearate is toxic to rats when administered orally and caused moderate skin irritation in rabbits.


While cats don’t need a lot of carbohydrates in their food, glucose is essential for their metabolism, so some amounts of sugar are necessary in their diet. Excessive amounts of sugar or any carbs can increase the risk of obesity and feline diabetes.


Dextrose is a crystallized form of glucose. It’s added to pet food as a sweetener or to make the food look meatier. Excessive amounts of dextrose are unnecessary and may be harmful to your pet in the long run.


Too much sugar isn’t good for humans, and certainly not good for pets. Excessive amounts of glucose in cat food are best avoided.


Melamine is an industrial chemical that has no approved use as an ingredient in animal or human food in the United States. Nonetheless, it can still be found in some rice and wheat products.

FDA traced the melamine to products labeled as wheat gluten and rice protein concentrate imported from China and used as ingredients in pet foods. FDA also reported that Cornell University scientists also found melamine in the urine and kidneys of deceased cats that were part of a taste-testing study conducted for the pet food manufacturer, Menu Foods, in 2007.

Although melamine alone may not be the cause of illness and death in cats, melamine-related compounds, such as cyanuric acid are also found in pet food, and the interaction of these to substances can be very toxic, causing kidney failure.

cat food ingredients to avoid milk

Dairy products

As cats grow from kittens to adults, they lose the ability to digest dairy efficiently. Their bodies no longer produce enough lactase to digest milk, so it’s common for adult cats to be lactose intolerant. If cats eat dairy products, they can experience stomach upsets, vomiting, or diarrhea.


A small amount of onions in cat food isn’t likely to cause any health problems, but onions are completely unnecessary in feline diets. Experiments with lab animals have found that high amounts of onions can damage red blood cells and cause hemolytic anemia.


Although garlic is considered less toxic for dogs than onions, garlic can still cause hemolytic anemia, research has shown. There is no nutritional need to include garlic in cat food.


Although it may not seem obvious, some of the most common allergens in cat food are protein sources, such as chicken, beef, and fish. Food allergies develop when an animal’s immune system misinterprets a food protein as an invader and reacts by activating an immune response.

As a result, pets can experience vomiting, diarrhea, or skin infections. It’s interesting to note that grains are an uncommon cause of allergies in pet food, as pets most often develop allergies to animal protein.

Takeaways on ingredients to avoid in cat food

Reading cat food labels can help you determine whether a particular food is the right option for your kitty. Although these ingredients aren’t necessarily harmful to your cat, too much exposure to them can have negative consequences.

Whenever you’re in doubt about a certain ingredient or a product, it’s always best to consult your vet.

Ana Markovic