What Foods Can Be Toxic or Unhealthy for Dogs

hen safely feeding your dog, it is important to learn to differentiate between foods that have some degree of toxicity, foods that can potentially cause internal injuries, foods that can cause allergic reactions, and foods that are generally unhealthy and should be avoided.

If you're interested in canine nutrition, Dog Learner has created several educational articles about the various diet options for dogs, a guide to teach you how to read commercial dog food labels, and the answers to the most common questions about dog food.

We should expect that the foods we feed our dogs help support their health, wellness, and vitality. As a minimum, food must be safe —meaning that it will not cause nutrient deficiencies, toxicities or imbalances—and not adulterated with non-food components (deliberately or unintentionally).

For anyone interested in dog nutrition, I recommend watching "Pet Fooled", a documentary available on Netflix and Amazon Prime on the unregulated pet food industry and the controversies around pet diet. Dr. Karen Becker and Dr. Barbara Royal, two prominent integrative wellness vets,  provide important insights into the dark side of the pet food industry and what kind of diet is good for our pet.

Foods that are toxic to dogs

In practice, toxic food can have various effects, from mild gastrointestinal inflammation to liver failure. The following foods should be considered potentially harmful for dogs and can cause various levels of intolerance depending on the dog and on the amount ingested.

• Xylitol is a sweetener contained in candy, gum, toothpaste. It can cause your dog's blood sugar to drop and can cause liver failure.
• Onions and garlic can cause digestive intolerance and severe anemia.
• Grapes and Raisins can cause vomiting or diarrhea, and in rare cases liver failure.
• Avocados contain a toxic substance for dogs, and large pits that can be swallowed.
• Chocolate or any food containing caffeine have side-effects and should be avoided.
• Fruits with pits like peaches, apricots, and plums should be kept away and considered dangerous if the pit is ingested.
• Milk and dairy products can cause digestive intolerance because dogs lack the enzymes needed to digest lactose present in animal milk.
• Nuts should be avoided because the fats they contain can cause vomiting and diarrhea.

Dog foods that can cause injuries

In this category, dog chews are the most common culprits. No dog chew is 100% safe, but some are especially dangerous. As a rule of thumb, safe dog chews should be natural, digestible, soft, and pliable.

You should avoid:

• Indigestible chews made of hard plastic or nylon. Chews that are too hard, can break or splinter and can cause tooth fractures, oral or internal abdominal injuries.
• Animal hooves, antlers, and bones: Hard animal parts, and particularly cooked bones, pose the most significant risk to your dog's teeth and gastrointestinal tract. If your dog doesn't break a tooth first, he could snap off a piece and ingest it. Large and fresh raw bones (beef marrow bones or chicken legs) are relatively safe and are good for a dog’s oral hygiene, but there is always a risk of injury if the bone splinters.
• Rawhide is controversial. It is the inner soft layer of an animal, most commonly cows. Many dogs will do fine with rawhide, but large pieces are difficult to digest and can cause gastrointestinal blockage. Besides, rawhide is produced by treating sourced products with potentially harmful chemicals.

Choose instead:

Instead of highly processed treats, you should buy  natural organic beef jerky, beef dental chews, natural meat rolls, organic chicken hot dogs, or natural treats made with liver, beef, or chicken with only natural preservatives added, and no sugar or salt.

Dog foods that are unhealthy

Any commercial (dry or wet) pet food or dog treat that contains highly processed starches, synthetic preservatives, coloring, flavoring, salt, and sugar should be considered unhealthy for your dog —in the same league as junk food. If you read the ingredient list, you'll notice that most dog treats sold in pet stores fall in that category.  

The quality of ingredients and price range of kibble —or dry extruded foods— can vary a great deal. Kibble is very convenient, but what you should consider from a nutritional standpoint, is that if you choose to feed your dog this type of food every single day of his life, convenience potentially comes with adverse health consequences. The thing to remember —in spite of the fancy branding, appetizing photos and marketing claims— is that dry foods are highly processed and primarily contain starches (on average 70%) and low grade protein meal. Dogs who are fed exclusively on kibble are prone to digestive problems and obesity because of the high starch (glucose) content.

If you decide to feed kibble, brands should be chosen cautiously by reading the ingredient list on the labels and the nutritional statements and ignoring brand claims.

While preservatives are needed in food, artificial preservatives such as BHA, BHT, or ethoxyquin should be avoided. Instead, select foods preserved with vitamin E and other naturally-occurring antioxidants such as rosemary and citric acid.

Dog food allergies

Allergies to grains in dogs are widely exaggerated. Interest in grain-free foods appears to have its origins in increased recognition and diagnosis of gluten intolerance in humans.

Mostly, grain-free is a marketing plot to sell dry food at premium prices. Foods that are advertised as “grain-free” are those that exclude grain sources such as wheat, corn, rice, barley, and oats. Grain-free products include starches from other plant sources such as potato, peas, or tapioca. Some grains contain gluten (cereals such as wheat, oats, and rye) while others don’t (corn and rice).

While a very small number of dogs may develop a disorder called gluten-sensitive enteropathy (similar to Celiac disease in humans), this is a rare genetic disease that occurs primarily in Irish Setters and is rarely diagnosed in other breeds.

When it comes to grains, the main issue for dogs is not allergy, it's digestibility. Digestive sensitivity varies according to the size and breed of dogs, with significant anatomical differences. Large breeds have a much lower relative mass of gastrointestinal tract (2.8% of body weight) compared with that of small breeds (7%). Research studies have shown that large breeds better tolerate refined flours based on corn and rice, while small breeds are better fed on cereals, and need lower amounts of fiber in their diet.

Despite current consumer biases toward gluten-free products, the fact is that current scientific studies of food allergy in dogs have shown that beef, dairy products, and soy are the most common causes of dog food allergy.

If you want a healthier diet for your dog, instead of buying grain-free dry foods, switch your dog to a low carb, high protein home-prepared diet made with unprocessed fresh products.

Food contamination risks

The most common type of food contamination is microbial contamination with Salmonella. It’s is a fecal bacteria that can contaminate a wide variety of foods, including raw meat and poultry, eggs, unpasteurized dairy products, and commercially produced dog foods (both extruded and raw foods). It’s the most frequent reason for commercial food recalls, and can potentially contaminate dogs and humans alike, although in practice it has more serious health consequences for humans than for dogs.

Fresh meat served raw or cooked is susceptible to microbial infections if hygiene norms for storage and handling are not respected and if frozen meat is not preserved at the correct constant temperatures. In practice, we are more prone to get infected than dogs, but when using meat, precautions must be taken.

Another serious type of contamination that can affect processed foods (most specifically dry foods that contain plant ingredients), is aflatoxin, which is a toxin produced by a crop mold. The consumption of pet food that contains aflatoxin can lead to liver failure and can be irreversible and fatal. Corn is the crop that is more at risk for aflatoxin contamination, especially during heat waves, or when grains are stored for long periods before shipment.

Apart from choosing reputable brands or carefully preparing your food at home for your dog, there is not much that dog owners can do to prevent food contamination. The website Dog Food Advisor keeps an updated list of commercial dog food recalls.