Foods Dogs Should Not Eat

Foods That Are Toxic to All Dogs

Before we get into the foods that aren’t good for dogs with cancer, let’s briefly cover the foods that are downright toxic to dogs. The following are foods dogs should not eat at all, whether they have cancer or not:

• Avocado: Ingestion of avocado fruit, pits and leaves can cause vomiting, diarrhea and fluid build-up.^1,2
• Alcohol: Alcohol contains ethanol which can cause depression of the central nervous system, lethargy, vomiting and diarrhea. Dogs can be exposed through alcoholic drinks, rotting fruit, and uncooked dough due to yeast fermentation.^1–3
• Chocolate, coffee and caffeine: Caffeine is a methylxanthine, a class of chemical that can cause restlessness, vomiting, diarrhea, instability, and incontinence. In large amounts, these items can cause respiratory failure and death.^1–4 Chocolate and coffee both contain methylxanthines, so never give them to dogs.
• Grapes and raisins: Grapes and raisins can cause kidney failure and should never be fed to dogs in any amount. Symptoms after ingestion can include vomiting, diarrhea, lethargy and abdominal pain.^1,3–5
• Macadamia nuts: Ingestion of macadamia nuts can cause weakness, tremors, vomiting, and diarrhea in dogs that can last for up to 2 days. These nuts are often present in cookies and baked goods.^1–3
• Onions, leeks, and chives: Onions, leeks, and chives are present in many dishes and can cause vomiting, diarrhea, excessive salivation and pale gums in dogs. They can damage red blood cells and cause anemia, and it may take over a day for symptoms to develop.^1–3 Garlic, a cousin of onions and chives, should be used with caution and in small amounts. You can read more in our comprehensive article on garlic.
• Xylitol is a commonly used artificial sweetener found in gum, candy and baked goods. This ingredient is very toxic to dogs and can cause vomiting, dangerously low blood sugar, weakness, liver damage and death.^1–3
• Birch Sugar and/or Birch Sap is listed on labels when xylitol is extracted from plants, but xylitol is xylitol no matter the source, and should be avoided.^1-3,46

With that out of the way, let’s look closer at problematic foods for dogs with cancer.

Food Choices That May Be Problematic for Your Dog with Cancer

Dogs with cancer can be more susceptible to becoming sick from their diet than healthy dogs, so some things that might be fine for a healthy dog might be problematic for dogs with cancer. Let’s look at raw meat diets and diets deficient in (or unbalanced in) omega-3 fatty acids.

Raw Meat Diets

Raw meat diets could contain dangerous bacteria that can cause serious infections in dogs with compromised immune systems.

Dogs with cancer who are being treated with chemotherapy, radiation or have blood cell or bone marrow cancers often have compromised immune systems and are more likely to become sick from raw diets.

Raw meat diets are becoming more popular. However, there are pros and cons of such diets. Proponents of raw meat diets cite potential benefits like improved energy, shinier coat, and a reduced risk of conditions like pancreatitis, arthritis, and allergies.

But the dangers of feeding raw diets may outweigh the benefits, especially for dogs with cancer.⁶

The biggest concern with feeding a raw diet is the risk of bacterial contamination. Multiple studies have shown that both homemade and commercial raw meat diets can contain a variety of microbes that can make pets and people sick like Salmonella, E.coli, Clostridium species and others.⁷

Contaminated food can make healthy dogs sick but poses a potentially fatal risk to dogs with weakened immune systems like dogs with cancer.

Common methods of storage and preparation like freezing, freeze-drying and high-pressure pasteurization may reduce the amount of bacteria present, but does not eliminate them.⁶

Nutritional imbalances can result from feeding raw diets exclusively. Many raw meat diets have imbalances that can include an inappropriate calcium to phosphorus ratio, levels of vitamin D twice the recommended amount and deficiencies of vitamin A and E.⁶

Most veterinarians are wary of the risks of feeding raw meat diets, but others have had positive experiences with them.^7,8 If you are feeding your dog a raw meat diet, or thinking of switching to one, it’s important to ask your veterinarian and get advice about how to make it complete and balanced and safe. In general, it’s probably best to avoid giving these to your dog with cancer.

A Deficiency/Imbalance of Omega-6 and Omega-3 Fatty Acids

Omega-6 and omega-3 fatty acids have many important functions in the body. A deficiency in omega fatty acids or an imbalance in the omega-6 and omega-3 fatty acids can cause increased inflammation, weakening of the immune system and other effects that can worsen symptoms in dogs with cancer.

Omega-6 and omega-3 fatty acids are the most well-known polyunsaturated fatty acids. They are considered essential in the canine diet because they cannot be made by the body and have to be eaten instead.^9,10

It is important for dogs with cancer to have the right amount and ratio of omega-6 and omega-3 fatty acids in their diets because they have many functions in the body and are important for a healthy immune system.

Excessive amounts of omega-6 fatty acids can increase the risk of conditions like cancer, cardiovascular disease and inflammatory and autoimmune diseases.^9–14

Diets that are extremely low-fat, unbalanced or homemade can cause a fatty acid deficiency. Symptoms of a fatty acid deficiency can include hair loss, scaly skin, bruising, poor growth, and nervous system abnormalities.¹⁰

Supplementation of fatty acids, especially omega-3 fatty acids, can improve symptoms from many diseases including cancer, skin disease, gastrointestinal disease and orthopedic diseases like arthritis.^9–11

Food Items That May Contribute to Cancer Risk

There are some food items and ingredients that can increase your dog’s risk of developing cancer. Cooking meats and baked foods at high temperatures, artificial preservatives, artificial antioxidants and artificial colorings can all increase the risk of cancer.

Here are some things to avoid if your dog has cancer.

Foods Cooked at High Temperatures

Heterocyclic amines and polycyclic aromatic hydrocarbons are chemicals that are formed when meat like beef, pork, fish or poultry is cooked at high temperatures like when grilling or pan frying over open flame.

Both types of chemicals have been shown to induce changes in DNA. When these chemicals change DNA, they increase the risk of developing cancer. This risk increases when meat is cooked at temperatures above 300°F or for a very long time.¹⁵

• Heterocyclic amines are created through the reaction of amino acids, sugars and creatine or creatinine from muscle tissue at high temperatures.
• Polycyclic aromatic hydrocarbons are created when juices and fat from meat drip onto the heat source causing smoke or flame.
• Polycyclic aromatic hydrocarbons in the smoke can adhere to the surface of the meat. They can also be formed during other food preparation methods like smoking meats.¹⁵

Both heterocyclic amines and polycyclic aromatic hydrocarbons can cause cancer in animals.^15–17

• Rodents fed a diet with heterocyclic amines developed tumors in multiple organs such as the breast, liver, lung, colon and prostate.
• Rodents fed a diet with polycyclic aromatic hydrocarbons developed cancers like leukemia and tumors in organs like the skin, lungs and gastrointestinal tract.
• Even though the doses of both compounds were much higher than in a normal diet, they do show the potential of these compounds to trigger tumor development.

Dogs are not usually fed pan fried or grilled foods, but they are often fed diets of dry or wet food that has been cooked at high temperatures.

Heterocyclic Amines in Pet Food

The extrusion process is the manufacturing technique used to form kibble. Extrusion uses high heat to kill bacteria in the food.¹⁸

One study looking at commercial pet foods found that the amounts of heterocyclic amines in pet food were similar to the amount found in the human diet.

However, since pets typically eat the same diet for all their meals, pets are actually receiving a dose of heterocyclic amines 5 times higher than people are.¹⁹

How to Limit Heterocyclic Amines

There are some things you can do to reduce the amount of heterocyclic amines that you and your pet consume when cooking at home.

Using microwave ovens as a cooking method for meat can reduce the amount of heterocyclic amines in the food. If you are cooking meat in the pan, you can reduce the amount of heterocyclic amines by turning meat frequently (every minute or so).^19,20

Supplementing a diet with soy-isoflavones has been shown to reduce the development of heterocyclic amine-induced breast cancer in people.

Soy-isoflavones can act as antioxidants and can reduce body fat in dogs. Soy is not a typical ingredient in pet foods, but pet food companies have been coming out with new formulations with soy designed to help pets lose weight that may also reduce the risk of cancer.^16,21

Acrylamide in Pet Foods

Acrylamide is a chemical in baked and fried starchy foods. It is produced by a reaction between the amino acid asparagine and sugars at high temperatures over 248°F.

Acrylamide is a known carcinogen and caused multiple forms of cancer including mesothelioma and thyroid gland carcinoma when rats were given acrylamide in their drinking water.^22,23

In one Japanese study looking at acrylamide in dog food, the chemical was found in all food samples including both dry kibble and canned varieties.

Acrylamide formation in dog food is likely related to the manufacturing process, particularly for dry food where high heat and pressure are used to sterilize, extrude and dehydrate powdered ingredients into kibble form.²³

Canned products are also exposed to high heat and pressure for sterilization during the sealing process.

The levels of acrylamide in the dog food samples were similar to those found in human food products. However, because dogs are usually fed the same diet for all of their meals, their daily exposure when fed only kibble ends up being 4 times higher than in a typical person’s diet.²³

Even though acrylamide was found in all of the dog food samples, there was significantly more in dry food than in canned food.

Therefore, feeding food that has been boiled, like canned food, in addition to dry kibble can reduce your dog’s risk of developing cancer due to acrylamide exposure.²³

Avoid Nitrate and Nitrite

Preservatives are used in human and animal food products to reduce bacterial growth and prevent spoilage to increase the shelf-life of the item. Nitrate and nitrite have been used as food preservatives for many years and can also be found in cereal products, vegetables and cured meats.

Nitrate can be reduced into nitrite by bacteria in the mouth and can then form N-nitroso compounds in the acidic environment of the stomach.^24,25

N-nitroso compounds are one of the most broadly acting and potent group of carcinogens in animal studies.²⁶

In rodent studies, an increased risk of cancer occurred when mice were given nitrites but not when given nitrates only. In people, studies show a connection between nitrite consumption and the development of stomach and esophageal cancer.

A 3-fold increase in the risk of infants developing brain tumors was seen when the mothers consumed a high amount of nitrites through cured meat or drinking water when pregnant.^24,25

The reaction that produces N-nitroso compounds can be inhibited by the ingestion of vitamin C. Vitamin C acts as an antioxidant and prevents the formation of dangerous N-nitroso compounds forming from ingested nitrites.^25,27,28

Avoid Artificial Antioxidants

Lipids (fats) break down in the presence of oxygen. Their presence often limits how long food can be safely stored. Lipid breakdown causes foods to become rancid and affects the scent, taste, color and shelf life of the food item. To combat this, producers often turn to antioxidants, which counteract the oxidation process and keep food stable for longer.

Natural antioxidants like vitamin C, flavonoids and tocopherols can help reduce the breakdown rate, but are often enough to preserve freshness and extend the shelf-life on their own.²⁹

Less expensive to use and rich in antioxidant qualities, synthetic antioxidants were developed like ethoxyquin and BHA (butylated hydroxyanisole).²⁹ However, these may not be the safest choice for food preservation.

These compounds can reduce the development of cancer in mice, rats and hamsters at low concentrations, but high concentrations can increase the risk of cancer and other adverse health effects, especially for ethoxyquin.

Ethoxyquin Exposure

Effects of high ethoxyquin exposure include kidney, liver, thyroid and reproductive problems, allergic reactions and skin and hair abnormalities. These effects occur in most animal species, but dogs are the most sensitive.²⁹

Ethoxyquin is not permitted to be used in foods intended for human consumption but is still found in spices like paprika and chili powder and some fish oil and fish meal. Ethoxyquin and its metabolites can also be found in farmed fish and poultry if their feed includes ethoxyquin. In the European Union, ethoxyquin has been prohibited as an additive for all species since June 2020.^29,30

Even though ethoxyquin cannot be used for human foods, and even though dogs are the most sensitive species, ethoxyquin is still used as a preservative in canned pet food and feed for fish and poultry.

When present in pet food, the FDA has set a limit of the ethoxyquin content at 150 parts per million (ppm) and requires a statement on the packaging indicating the presence of ethoxyquin.

Setting a limit on the amount of ethoxyquin is important, but the minimal amount needed for signs of toxicity in dogs was found to be 100 ppm. This means that negative effects of ethoxyquin can still occur in dogs while still being within legal limits.^29,31

Butylated Hydroxyanisole (BHA) Exposure

The negative effects of butylated hydroxyanisole (BHA) are less clear.

Butylated hydroxyanisole is classified as a carcinogen by the National Toxicology Program and the International Agency for Research on Cancer (IARC), but a deeper investigation tells a different story.

Butylated hydroxyanisole was shown to cause cancers like papillomas and squamous cell carcinomas in the forestomachs of rodents like rats, mice and hamsters after chronic exposure.

Even though cancers occurred, the effects of butylated hydroxyanisole were only seen in species having a forestomach.

In species without a forestomach, such as guinea pigs and monkeys, no toxic effects or tumors occurred. Therefore, the toxic effects of butylated hydroxyanisole are not likely to occur in people or dogs because we do not have forestomachs.^32,33

Natural Antioxidant Alternatives to Ethoxyquin and BHA

There are some natural alternatives to the artificial antioxidants that can be used in pet food. Some examples of naturally derived antioxidants include mixed tocopherols from soybean oil, vitamin C, citric acid, marigold extract, rosemary extract, curcumin and grapeseed extract among others.^18,36,37

Mixed tocopherols from soybean oil have the highest efficacy of the natural antioxidants at protecting fats from degrading. However, tocopherols are not as effective as the synthetic antioxidants at prolonging shelf-life because they are easily degraded.¹⁸

Vitamin C is a well-known antioxidant that has many different uses but when used alone is not able to protect fats as well as other alternatives because it is water soluble.¹⁸

Rosemary extract has excellent antioxidant capabilities and is used widely in products like meat, seafood, poultry and baked goods. It has an enhanced effect when used with tocopherols, citric acid and vitamin C.^36,38

Curcumin, a compound found in turmeric, is effective at preventing fat oxidation even at low doses and can be more effective than butylated hydroxyanisole.^18,36–38

The limitations of the naturally derived antioxidants are their higher cost and their reduced ability to withstand the harsh processing involved in pet food manufacturing like high heat, steam and pressure. More research is still needed to find a naturally-derived antioxidant that is as effective and as low cost as the artificial alternatives.¹⁸

Reduce Artificial Colors

Artificial coloring is used for human food products but is also added to pet food. Dyes and colorings in pet food are added to make the product more appealing to owners and do not typically provide a nutritional benefit for pets.

The Food and Drug Administration (FDA) regulates all food additives and separates food colorings into two categories: Exempt colors which are pigments derived from natural sources like plants, animals, and minerals and Certified colors which are synthetic color additives.

There are currently eight certified color additives which include FD&C Blue No. 1 (Brilliant Blue), FD&C Blue No. 2 (Indigo Carmine), FD&C Green No.3 (Fast Green FCF), Citrus Red No.2 (only used for orange peels), FD&C Red No. 3 (Erythrosine), FD&C Red No. 40 (Allura Red), FD&C Yellow No. 5 (Tartrazine), FD&C Yellow No. 6 (Sunset Yellow).^18,39

Even though the FDA considers multiple factors when approving artificial colors, there is still concern about the effects of these products on the health of both animals and people.^39,40

Even though studies on rats and mice are performed to determine the maximum amount that can be used safely, negative health effects seen in these animals might indicate that the pigment should not be used at all. The following is a list of some concerns regarding the certified color pigments:⁴⁰

• FD&C Red 3: The FDA concluded in 1990 that Red 3 is an animal carcinogen after thyroid tumors were found in rats. However, the FDA has not yet removed it from the approved list.^40,41
• FD&C Red 40: Red 40 is the most widely used synthetic color additive and there is some controversial evidence that it can cause a worsening of tumors in the reticuloendothelial system in mice.⁴⁰
• FD&C Yellow 5: Yellow 5 is the second most widely used synthetic dye and batches of the dye have been shown to be contaminated with carcinogens like benzidine and 4-aminobiphenyl. Yellow 5 has been known to cause allergic hypersensitivity reactions in people, causing the Joint Council of Allergy and Immunity to urge the FDA to ban the additive in 1986.⁴⁰
• FD&C Yellow 6: This additive has not been found to be an animal carcinogen but did result in ocular changes such as eyelid crusting, corneal inflammation and corneal opacity in a 7-year study with Beagles in the 1960’s. Due to this study, Kent Davis, an FDA veterinarian, recommended the immediate decertification of the color, which did not occur.⁴⁰
• FD&C Blue 2: Studies of Blue 2 showed significant increases in malignant mammary tumors and brain gliomas in rats. However, the study determined it wasn’t an animal carcinogen because additional biological factors that would directly link the two were not observed. Even so, Dr. William Lijinsky, a cancer researcher at the NCI’s Frederick Cancer Research Center, concluded that Blue 2 is a carcinogen because gliomas are so rare in rats.⁴⁰
• FD&C Green 3: Studies of Green 3 showed significant increases in bladder transitional cell cancer and testes Leydig’s tumors in male rats. However, these results were not considered sufficient for banning the additive.⁴⁰

Healthier Color Alternatives

Naturally based colorants have become more popular due to concerns about artificial dyes, although they are typically not as bright as the artificial ones or as stable to heat, light and oxygen.

Naturally derived colorants may provide some nutritional benefits where the artificial ones do not. The following are some natural sources of color that have been successfully added to foods:⁴²

• Red Hues: Some sources of naturally derived red colorants are anthocyanins from grape-skin extract, betacyanins from beet juice concentrate, carmine from the cochineal insect and tomato lycopene extract.⁴² Wondering if anthocyanins from grape skins are safe for dogs, given that grapes aren’t? A study looked at this issue, and found that they are safe, even though they are extracted from grapes.⁴⁷
• Yellow/Orange Hues: Yellow pigments can be created from carotenoids derived from algae, fungi, paprika, carrot oil and chemical synthesis, saffron, annatto from the seed of the tropical tree Bixa orellana, and curcumin from turmeric.⁴²
• Green/Blue Hues: Green coloring can be attained by adding chlorophyll, usually derived from dried alfalfa and blue hues can be obtained by adding iridoid pigment derived from the gardenia plant.⁴²
• Finally, brown coloring can be added by using caramel and toasted partially defatted cooked cottonseed flour.⁴²

Avoid Any Foodborne Illness

There are measures you can take to prevent your dog and family from being exposed to harmful bacteria. If you are preparing meat for your dog to eat at home, you should make sure to practice safe handling and cleaning procedures in your home.

• When you store raw meat in your refrigerator, you should keep the meat packaged and located on a bottom shelf to avoid the risk of juices leaking onto the other items in your fridge, causing cross contamination.
• When you are ready to prepare the meat for cooking, you should avoid washing the items because this can cause contaminated water to splash onto other surfaces in your kitchen.
• If you need to cut the meat, you should make sure to use a cutting board for the raw meat only and do not use it for cutting other food items until it has been properly cleaned.
• When you are ready to clean your kitchen surfaces, you should thoroughly clean with either hot soapy water or ¼ cup of chlorine bleach per quart of water. Surfaces commonly contaminated include kitchen countertops, utensils, bowls and cutting boards.^43,44
• Cutting boards can be cleaned by washing them with hot, soapy water after each time you use them. You should then allow them to air dry or pat them down with clean paper towels.
• If you want some extra cleaning power, you can use 1 tablespoon of chlorine bleach per gallon of water and then fully cover the surface of the board with the solution. You should then allow it to rest for several minutes before rinsing and patting dry.
• If you have a dishwasher, acrylic, solid wood, glass and plastic boards can be cleaned in the dishwasher. Make sure not to put laminated boards in the dishwasher because they can crack or split, making them more difficult to clean for future uses.⁴⁵
• After handling raw meat you should wash your hands thoroughly with soap and water for at least 20 seconds.⁴³
• When cooking meat, it is important to bring the internal temperature of the meat to a safe level to kill any bacteria.
• Cuts of beef, lamb and pork should be cooked to an internal temperature of 145°F. Ground beef and pork should be cooked to 160°F.
• Fish should be cooked to an internal temperature of 145°F.
• Poultry products should be cooked to 165°F.⁴⁴