(Dr. Iulia Mihai, DVM) One of our missions as devoted pet owners is to ensure that the food we provide is safe, nutritious, and supports their long-term health. With so many types and brands of food available, it can often be difficult to decide which one to choose. However, keep in mind that many commercial foods contain questionable ingredients and additives that can put your dog’s and cat’s health at risk. So, it’s essential to understand not just what ingredients are in your pet’s food, but also whether they provide the essential nutrients they need. 

Label navigation can often be difficult, making choosing a quality diet a real adventure. This article highlights the key red-flag ingredients that all pet owners should recognize and avoid.

Questionable Ingredients to Watch For

1. Low-quality proteins and by-products

Many pet food brands choose to use low-quality proteins, such as those from meat by-products. These are used instead of real proteins (such as meat itself) to keep production costs down. While the food will have a higher calorie and protein content, it will be of lower quality. Therefore, choose brands that say “chicken meat” or “lamb meat” on the label, for example, and not “meat by-products” or “meat meal”. 

Pet food brands that list meat meal or animal by-products first and then other ingredients should be avoided. When the source of the meat is not specified, you will never really know what your dog or cat is eating. Moreover, when meat is the first ingredient on the label, it means that it was the heaviest ingredient before processing.  Therefore, diets with meat and meat by-product as first and second ingredient may contain more animal-based material, which can contribute to a higher protein content. However, ingredient order alone does not guarantee nutritional balance or protein quality.  

2. Excessive fillers and carbs

Dogs and cats do not need carbohydrates in their diet. It is not a biological need. In the wild, most of the diet of wild dogs and cats consists of protein and fat (and not grains, peas, corn, etc.). Starches and carbs are often added to pet foods as fillers (cheap ingredients that help reduce production costs and improve shelf stability).

Diets high in these ingredients can increase the risk of diabetes, obesity, and even cancer over time. This is especially concerning for cats, who are obligate carnivores and metabolically adapted to very low-carb diets. In addition, these diets high in carbs can also lead to digestive problems manifested by gas, bloating, abdominal pain, diarrhea or constipation, and food intolerances.

Even high-protein foods can contain hidden starches. Therefore, it is essential to read the label carefully. A proper diet for your dog or cat should be built around animal proteins and fats rather than plant-based fillers.

3.  Artificial preservatives and color

BHA (butylhydroxyanisole), BHT (butylhydroxytoluene), and ethoxyquin are artificial preservatives commonly used in pet food to extend shelf life. These preservatives can cause serious health problems for your dog or cat, especially ethoxyquin. Long-term exposure to these chemicals has been linked to cancer and other health problems in pets.

Animal studies have shown that it can cause serious damage, especially to the kidneys and bladder. Studies in rats have found signs of tissue damage and early-stage cancer development, suggesting that ethoxyquin may have carcinogenic potential. In terms of carcinogenicity, ethoxyquin has shown conflicting effects: it can both promote and inhibit genetic changes linked to cancer.

Food colorings are found in both human and pet foods. Colors such as caramel color, Red 40, Blue 2, Yellow 5, and Yellow 6 are known to lead to allergies, behavioral problems, and cancer in humans and animals. Artificial colors provide no nutritional benefits and can compromise the health of pets.

Read the label carefully and if you see these ingredients, avoid buying the product.

4. Sweeteners and sugars

Artificial sweeteners in large quantities can be dangerous to your pet's health. Avoid giving your dog or cat pet food that contains artificial sweeteners and keep them away from sweets that contain xylitol, a deadly toxic substance for pets.

Fun fact: Cats cannot perceive sweet flavors like sugars the way humans or dogs can. They are missing functional sweet taste receptors.

5. Toxic contaminants

In pet food manufacturing, much like in human food production, various unintended substances can end up in the final product, even though they are not part of the original formula or listed among the ingredients. Some of the substances that can be found in dog and cat food include arsenic, mercury, PCBs, BPA, dioxin, mycotoxins, lead, aluminum, uranium, and vanadium.

A recent study highlights serious concerns about toxic metal contamination in commercial pet food. It was found that 100% of the brands tested contained mercury above the maximum tolerable levels set by the FDA. Uranium and lead were also frequently found in dangerous amounts, especially in dry foods.

6.  Sulfites and sulfur dioxide

Pet food manufacturers add sulfur dioxide and sulfites (chemical preservatives) to fresh or raw pet food to extend shelf life and maintain the red color of the product. One of the main risks associated with these preservatives is thiamine (vitamin B1) deficiency – thiamine is an essential nutrient for the functioning of the nerves and metabolism of dogs and cats.

One study found that 5 dogs (7 weeks to 6 years of age) developed thiamine deficiency after being fed meat treated with sulfites. The dogs showed low appetite, weight loss, vomiting, and neurological signs such as seizures, incoordination, and eye movement abnormalities. Most dogs recovered quickly with vitamin B1 treatment. Unfortunately, one puppy was euthanized, and a necropsy showed brain damage consistent with thiamine deficiency.

Another study shows that a cat developed probable dietary-induced thiamine deficiency after being fed commercial kangaroo meat containing high levels of sulfur dioxide preservatives (tests confirmed it). The cat showed sudden neurological symptoms such as muscle twitching and inability to stand. The cat's condition improved with thiamine supplementation.

Choose brands that clearly specify preservation methods and avoid products containing sulfites or sulfur dioxide for your pet’s safety.

7. Unhealthy fats and rendered oils  

Unhealthy fats in pet food include rendered fats and vegetable oil. Rendered fats can contain toxins and can become a breeding ground for dangerous bacteria or mold, putting your pet’s health at risk. Vegetable oil, on the other hand, has low nutritional value and can promote inflammation, especially in cats and dogs with joint conditions such as arthritis.

Additionally, leftover fats and lard are not suitable for pets as they can lead to digestive problems such as diarrhea or intestinal discomfort.

Bottom Line

A balanced diet provides essential health benefits for your cat or dog. Without the right amounts of vitamins, minerals, fats, and proteins in their diet, your pet can develop severe health problems. Choosing a diet that contains the right nutrients for your pet's age, breed, and health status will help keep them healthy (or stable) and happy. Talk to your veterinarian about the ideal diet and the best food for your pet. To ensure you are feeding your pet correctly, consult your vet for guidance on the best diet to purchase and the appropriate portion sizes to feed them.

Your veterinarian can better provide you with a nutritional plan and help you track, maintain, and manage your pet's ideal weight.

Iuliana graduated from the University of Agronomical Sciences and Veterinary Medicine in 2012, Romania. She has a Master’s degree in Small Animal and Equines Pathology and a strong affinity for Veterinary Parasitology and Laboratory. In 2013 she started her Ph.D. in epithelial cancer in dogs and cats. She volunteered at the faculty’s clinic in her 3rd year of study, and continued her career in small animal pathology and laboratory. She has one cat and eleven rats. Her interests outside of work include traveling, writing, and crafting.