What's Hiding in That Bag of Pet Food?

If you share your life with dogs or cats, you’ve probably spent time reading pet food labels, comparing protein percentages, or searching for formulas marketed as “premium,” “natural,” or “complete and balanced.” A newly published study examining commercial pet foods¹ reveals how hidden contaminants and biologically active compounds can accumulate in pets over time from eating processed diets.

Researchers screened commercial dog and cat foods and discovered significant variation in metabolite profiles between feed categories. Standard commercial diets contained higher levels of Fusarium-derived mycotoxins, phytoestrogens, and plant metabolites than some specialized diets formulated for seniors or digestive support. While toxin levels remained below current regulatory guidance values, the study raises important concerns about chronic exposure, species sensitivity, and the long-term biological impact of ultra-processed pet food.

Cats appeared substantially more vulnerable to certain toxins than dogs. This study reinforces what integrative veterinarians have observed for years: food is either building health or slowly eroding it. And for many pets eating heavily processed diets day after day, year after year, the cumulative burden matters.

Understanding Mycotoxins in Pet Food

Mycotoxins are toxic compounds produced by molds and fungi. Many are generated by Fusarium species, which commonly contaminate grains and plant ingredients used in commercial pet food manufacturing.

Common mycotoxins include:

These contaminants are not intentionally added to pet food. They develop when crops are exposed to moisture, heat, poor storage conditions, or fungal contamination before and after harvest. The challenge is that modern kibble often relies heavily on commodity crops such as corn, wheat, rice, soy, peas, lentils, and other starch-rich ingredients, which are especially vulnerable to mold growth and toxin formation.

Even though manufacturers test for some contaminants, no dry food is entirely free of toxins. The study found that nearly all feed categories contained multiple mycotoxins simultaneously. While individual levels remained below established “safe” thresholds, regulatory limits are typically based on acute toxicity data — the amount needed to trigger immediate illness or death. But chronic, low-level exposure over months or years can produce entirely different biological effects that are harder to measure.

Corn-Based Ingredients and Pet Food Risks

A concerning reality in modern pet food manufacturing is the industry’s heavy reliance on commodity crops, especially corn. Corn and corn-derived ingredients have repeatedly been linked to some of the largest, deadliest pet food contamination events in modern history because they are particularly vulnerable to fungal growth and mycotoxin production during cultivation, storage, and transport.

Aflatoxins, toxic compounds produced by Aspergillus mold species, are among the most dangerous contaminants associated with corn-based pet foods. These toxins are potent liver poisons and carcinogens that can accumulate in animal tissues over time.

In 2020 and 2021, one of the largest aflatoxin-related pet food recalls in recent history involved corn-contaminated Sportmix products manufactured by Midwestern Pet Foods.

According to FDA reports², more than 110 dogs died, and over 210 became ill after consuming contaminated food. Investigators traced the contamination to mold toxins associated with corn ingredients used in the manufacturing process.

Another major recall involving aflatoxin-contaminated corn occurred with Sunshine Mills products, affecting numerous dog and cat food brands distributed nationwide. FDA investigators traced the contamination back to a single load of mold-contaminated corn used during manufacturing³.

A pet food recall in 2007, one of the largest pet food disasters ever recorded⁴ , also involved contaminated plant ingredients, including corn gluten, which was linked to kidney failure cases in pets in South Africa. Worldwide, thousands of pets were believed to have been affected after exposure to contaminated ingredients used in commercial pet foods.

Pets are often fed the same foods every day for months or years. Unlike humans, who typically consume varied diets, dogs and cats may repeatedly encounter the same contaminated ingredients over long periods. The FDA itself warns that aflatoxins can accumulate in pets that continuously consume contaminated food.

This is one reason I strongly encourage minimizing biologically inappropriate fillers such as corn in canine and feline diets whenever possible. Corn is inexpensive and widely used in ultra-processed pet foods because it helps manufacturers reduce production costs and supports extrusion during kibble manufacturing. But from a biological standpoint, it offers limited species-appropriate nutrition for carnivorous animals while increasing the risk of exposure to mold toxins and inflammatory compounds.

Fresh, moisture-rich, minimally processed diets built around high-quality animal proteins dramatically reduce reliance on high-starch commodity ingredients, which are most vulnerable to mycotoxin contamination. Rotating brands and protein sources and increasing dietary variety can also help reduce chronic exposure to any single contaminated ingredient over time.

It’s important that we don’t vilify these ingredients; corn itself is not toxic, and sharing some fresh corn this summer with your pup is entirely safe and fine (Homer loves a bite of corn cut off the cob), but when it’s included as a top ingredient in a pet food, it becomes metabolically stressful.

Why Cats Are More Vulnerable

Researchers exposed canine and feline immune cells to various mycotoxins in laboratory testing. Feline cells showed significantly greater susceptibility to damage from deoxynivalenol (DON) and especially zearalenone (ZEN).

This finding aligns with what veterinary toxicologists already know about cats: felines possess unique metabolic limitations that make them less efficient at detoxifying certain compounds.

Cats have reduced liver glucuronidation capacity, which means they process many toxins differently from dogs and humans. This metabolic limitation is one reason cats are notoriously sensitive to medications, essential oils, environmental chemicals, and food contaminants.

This means that a level of exposure considered “acceptable” for one species may not be harmless for another. Cats are obligate carnivores designed to thrive on moisture-rich animal tissue, not heavily processed plant-based ingredients. Yet many commercial feline diets contain substantial amounts of grains, legumes, and starches that contribute little biological value while increasing the potential for exposure to contaminants.

The study also identified zearalenone as particularly problematic because it acts as a phytoestrogen-like compound. These substances can interfere with hormone signaling and endocrine balance.

Over time, endocrine-disrupting compounds can influence:

• Reproductive health
• Thyroid function
• Immune regulation
• Metabolic balance
• Inflammatory pathways

Even when exposure remains below “toxic” levels, biologic disruption can still occur.

Good Carbs, Bad Carbs, and the Problem With Ultra-Processed Pet Food

Most kibble and many canned diets are ultra-processed foods. Ingredients undergo repeated heating, extrusion, rendering, drying, pressure changes, and long-term storage. Every stage alters nutrient integrity and increases oxidation.

Processing also changes the food’s metabolite profile, the collection of biologically active compounds present in the finished product. The new study demonstrated that standard commercial diets often contained higher concentrations of plant metabolites and phytoestrogens than specialized therapeutic formulas.

Dogs, and especially cats, are not biologically adapted to consume large amounts of processed plant material as a source of starch. A species-appropriate diet for dogs consists primarily of animal protein, healthy fats, moisture, connective tissue, organs, and roughage (aka fiber). Cats require even more animal-based nutrition with minimal starch or carbohydrate intake.

Unfortunately, many commercial diets invert that ratio, relying heavily on inexpensive starches and plant proteins to reduce manufacturing costs. Some kibbles contain carbohydrate levels exceeding 40% to 50%.

That level of starch is biologically inappropriate for carnivorous species and contributes to multiple chronic diseases. When you add potential mycotoxin exposure and oxidation byproducts to the equation, the long-term health implications become even more concerning.

But don’t confuse high glycemic starch (bad carbs) with low glycemic, prebiotic fibers that dogs and cats need to maintain their microbiome (good carbs). 10-20% low glycemic roughage, in the form of dark green leafy and colorful veggies, herbs, spices, and high antioxidant berries, is a pet’s only source of food-based antioxidants, phytonutrients, and flavonoids that scavenge free radicals and feed the microbiome. Microbiome research is very clear: a small amount of high-quality plant material, rich in important prebiotic fibers the gut needs to feed a healthy microbiome, is essential for a balanced gut and metabolism.

Why “Below Regulatory Limits” Doesn’t Always Mean Safe

Pet parents often feel reassured when studies conclude toxin levels were “below guidance values.” But regulatory standards have limitations.

First, many thresholds are based on livestock production models rather than lifetime companion animal wellness. The goal in agricultural systems is often to prevent acute production losses rather than to optimize long-term health and longevity.

Second, regulations rarely account for cumulative exposure from multiple toxins interacting simultaneously.

Third, toxicology is highly individualized. Age, genetics, liver function, microbiome health, stress, medication use, and species-specific metabolism all influence susceptibility.

A young, healthy dog eating fresh food intermittently can tolerate low-level exposure far differently than a senior cat consuming the same ultra-processed kibble every day for a decade. Blood exposure levels were significantly lower than concentrations required to produce direct cellular toxicity in laboratory testing. That’s encouraging. But it does not eliminate concern regarding chronic inflammatory, endocrine, metabolic, or immune effects from lifelong exposure.

Pets today are experiencing unprecedented rates of chronic disease. Cancer, inflammatory bowel disease, allergies, obesity, diabetes, kidney disease, and autoimmune disorders have become increasingly common. Nutrition is not the sole cause, but it is unquestionably a major contributor.

The Gut-Immune Connection

Another overlooked issue involves the microbiome. The gastrointestinal tract houses a large portion of the immune system. When pets consume highly processed diets filled with inflammatory ingredients, oxidized fats, chemical residues, and low-grade contaminants, the intestinal barrier can become compromised.

Research increasingly shows that chronic dietary stress can alter microbial diversity and increase intestinal permeability, also known as “leaky gut.” This can contribute to chronic inflammation, allergies, skin disease, joint degeneration, and digestive disorders.

Fresh, minimally processed diets support a healthier gut ecosystem by providing natural enzymes, intact amino acids, bioavailable nutrients, antioxidants, and moisture. Living foods communicate differently with the body than ultra-processed pellets manufactured at extreme temperatures.

What to Feed Instead

A healthier diet for pets includes:

• High-quality animal protein
• Healthy animal fats
• Moisture-rich meals
• Organ meats
• Fresh, colorful vegetables, herbs, and spices
• Minimal starch
• Minimal synthetic additives
• Minimal processing

For cats especially, animal tissue should form the overwhelming majority of the diet. A nutritionally balanced, fresh-food diet can be homemade or commercially prepared, provided it is formulated correctly and uses high-quality ingredients.

If you feed kibble, there are still meaningful ways to reduce risk:

Rotating brands decreases repetitive exposure to the same contaminants and broadens nutrient diversity.

Alternate among:

• Different protein sources
• Freeze-dried raw foods
• Gently cooked diets
• Fresh toppers

Add Fresh Foods Daily

Even adding fresh whole foods to processed diets can improve nutritional quality.

Excellent additions include:

• Sardines packed in water
• Pasture-raised eggs
• Lean meats
• Heart
• Dark leafy greens and bites of fruit
• Berries
• Fermented vegetables 
• Bone broth

Fresh foods provide antioxidants and phytonutrients that help support detoxification pathways and cellular resilience.

Support Detoxification Naturally

The body already possesses remarkable detoxification systems, especially through the liver, kidneys, lymphatic system, skin, and gastrointestinal tract.

You can support these systems nutritionally with:

• Sulforaphane-rich broccoli sprouts
• Milk thistle
• Omega-3 fatty acids
• Antioxidant-rich vegetables
• Adequate hydration with pure filtered water

Appropriate Food Is Preventive Medicine

One of the most powerful forms of preventive veterinary medicine is biologically appropriate nutrition. The body has an incredible ability to heal, repair, detoxify, and regulate inflammation when given the proper raw materials. But that resilience weakens when pets consume diets high in ultra-processed ingredients and chronic, low-grade contaminants.

This research should not create panic. Most pets eating commercial foods will not suddenly develop acute toxicity. But the findings should encourage critical thinking about long-term nutritional exposure. Every meal matters. Every ingredient matters. And over the course of a lifetime, small daily choices add up to either vibrant health or chronic disease.

Dogs and cats evolved to consume a wide variety of foods, including meat-based diets rich in moisture, enzymes, connective tissue, organs, and highly bioavailable nutrients. Their biology still reflects those ancestral needs today. The closer we feed our beloved companions to nature, the more we support the systems that protect their health at the cellular level.

That’s why I continue encouraging pet parents to move away from heavily processed diets whenever possible and toward fresh, whole, species-appropriate nutrition that nourishes the body rather than merely meeting minimum nutrient standards.

Sources and References:

• ¹ Mycotoxin Research, 18 May 2026
• ² FDA Veterinary Pet Food Alert, Sportsmix
• ³ FDA Veterinary Pet Food Alert
• ⁴ Cornell Chronicle, April 2007

About Karen Shaw Becker, DVM, CVH, CVA, CCRT

Veterinarian Dr. Karen Shaw Becker believes biologically appropriate food and an animal's immediate environment are essential in determining health, vitality, and lifespan. She has spent her career as a wildlife and exotic animal veterinarian and small animal clinician, empowering animal guardians to make intentional lifestyle decisions to enhance the well-being of their animals.