Cat Food Ingredients to Avoid: The Definitive Blacklist

By Sarah Bennett, Certified Animal Nutritionist

The pet food industry is largely self-regulated in most countries, and while standards have improved significantly since high-profile recalls in the 2000s, the incentive to use cheap, shelf-stabilising, and palatability-enhancing ingredients remains strong. Some of these ingredients are genuinely harmful. Others are not acutely dangerous but are nutritionally inappropriate for an obligate carnivore. Knowing the difference — and knowing what to look for on a label — protects your cat.

BHA and BHT: Synthetic Preservatives with Carcinogenic Concerns

Butylated hydroxyanisole (BHA) and butylated hydroxytoluene (BHT) are synthetic antioxidants used to prevent fats from going rancid in dry pet foods. They are effective preservatives, which is why they remain common despite mounting concern about their safety.

BHA is listed as a possible human carcinogen by the National Toxicology Program in the United States. Animal studies have demonstrated tumour promotion effects in the forestomach at high doses. While regulatory bodies have maintained that levels permitted in pet food are low, the chronic, daily, lifetime exposure of a cat eating the same commercial food for years is a meaningful variable that short-term safety studies do not fully capture.

BHT has shown hepatotoxic and carcinogenic effects in rodent studies and is banned from food products in several countries. Its continued presence in pet food is a regulatory anomaly rather than a safety endorsement.

Safer alternatives exist: mixed tocopherols (natural Vitamin E), rosemary extract, and ascorbic acid are widely used as natural preservatives and carry no comparable concerns. If you see BHA or BHT on an ingredients list, choose a different product.

Ethoxyquin: A Pesticide in Your Cat's Bowl

Ethoxyquin was originally developed as a rubber stabiliser and pesticide. It later found use as a preservative in pet foods, particularly in fish meal. It is now banned from human food in the European Union and restricted in Australia and Canada, yet it may still appear in pet foods — or in ingredients (particularly imported fish meal) used in pet food manufacturing without being declared on the final label, since it was added before processing.

Studies have associated ethoxyquin exposure with liver and kidney damage, immune dysfunction, and reproductive issues. Cats, with their unique hepatic metabolism and limited ability to detoxify many compounds that other species handle safely, are particularly vulnerable to cumulative exposure from preserved fish ingredients. Look for it on labels and favour brands that explicitly guarantee ethoxyquin-free sourcing of all ingredients.

Carrageenan: Gut Inflammation Risk in Wet Foods

Carrageenan is a seaweed-derived thickener and gelling agent used extensively in wet cat foods to create a smooth, uniform texture. It is not a meat product — it is a filler that improves mouthfeel and product appearance at low cost.

The concern around carrageenan centres on its degraded form (poligeenan), which is classified as a possible carcinogen. While undegraded carrageenan is considered distinct from its degraded form in regulatory frameworks, peer-reviewed research has demonstrated that food-grade carrageenan can convert to its degraded form in the acidic environment of the gut. Studies in animal models have linked carrageenan consumption to intestinal inflammation, colitis, and impaired gut barrier function.

For cats with inflammatory bowel disease (IBD), chronic digestive upset, or sensitive stomachs, carrageenan deserves particular scrutiny. It is listed simply as "carrageenan" on labels — look for it in any pâté or gravy-style wet food.

Corn Syrup and Added Sugars: Empty Calories and Diabetes Risk

Cats lack sweet taste receptors and have virtually no nutritional use for simple sugars. Their metabolism is not equipped to efficiently process large carbohydrate loads, and their insulin response to glucose is less robust than in omnivores. Yet corn syrup and various sugar derivatives appear in some cat foods and treats, primarily as palatability enhancers and preservatives.

The consequences of chronic sugar exposure in cats mirror those seen in humans: obesity, insulin resistance, and ultimately Type 2 diabetes mellitus. Feline diabetes has become markedly more common in parallel with the rise of carbohydrate-dense commercial pet foods. Any product containing corn syrup, cane sugar, molasses, glucose, or similar sweeteners in its ingredients list should be avoided.

Meat By-Products: Not Always Bad, But Buyer Beware

The term "meat by-products" generates more controversy than it perhaps deserves — but only when understood correctly. By-products are the parts of the slaughtered animal other than skeletal muscle: organs, bones, blood, hide, intestines, and in the worst cases, tumours and diseased tissue. Some by-products are genuinely nutritious: liver, heart, kidney, and lung are organ meats with high biological value and are intentionally included in quality foods. Others — rendered material of unknown origin or quality — are nutritional filler.

The critical distinction is specificity. "Chicken by-products" is more informative than "poultry by-products," which is more informative than "meat by-products." The vaguer the term, the less traceable the source. Generic "meat and animal derivatives" (common in European labelling) provides essentially no information about what you're feeding your cat.

By-products are not inherently bad — wild cats eat the whole prey animal — but unspecified, low-grade by-product meals from unknown species are a reasonable concern.

Artificial Colours: Tartrazine, Red 40, and Blue 2

Artificial dyes serve no nutritional function in pet food whatsoever. Cats are not attracted to colour — they choose food by scent, texture, and temperature. Artificial colours such as tartrazine (Yellow 5), Red 40, and Blue 2 are added for the benefit of human consumers, who associate bright, consistent colour with freshness and quality.

Tartrazine has been associated with hyperactivity and behavioural changes in children and is banned or restricted in multiple countries. Red 40 and Blue 2 have shown potential carcinogenic effects in animal studies. More fundamentally, there is no reason these compounds need to be in your cat's food at all. Their presence signals a manufacturer prioritising shelf appeal over nutritional integrity.

Excessive Plant Proteins: Misleading Protein Percentages

Plant proteins — from corn, soy, wheat gluten, pea protein, and similar sources — are commonly added to boost the protein percentage on a cat food's guaranteed analysis without the cost of additional animal protein. This practice is deeply misleading for the cat owner who reads "30% protein" and assumes it means meat protein.

Cats evolved to use animal amino acids. Plant proteins have incomplete amino acid profiles relative to feline requirements, and even where individual amino acids are present, their bioavailability from plant sources is lower. A food deriving much of its protein from corn gluten or pea protein provides a nutritionally inferior protein package compared to one based on animal tissue, regardless of what the percentage on the label shows. Look at the first five ingredients: if plant-derived proteins appear prominently before named meat sources, consider it a red flag.

Propylene Glycol: Toxic to Cats in Some Forms

Propylene glycol is a humectant used to maintain moisture in semi-moist foods and some treats. While it is considered safe for dogs and humans at typical food levels, it is explicitly prohibited in cat food by the FDA in the United States due to its potential to cause Heinz body anemia in felines. Cats are highly sensitive to compounds that oxidise haemoglobin, and propylene glycol at sufficient doses triggers this destruction of red blood cells.

Its use in cat food is now rare in regulated markets, but it may appear in treats manufactured in countries with less stringent standards, or in products imported from regions where cat-specific regulations differ. Check the ingredients of any semi-moist treat carefully.

References

1. Tobacman JK. Review of harmful gastrointestinal effects of carrageenan in animal experiments. Environmental Health Perspectives. 2001;109(10):983–994. PMID: 11675262.
2. Center SA. Metabolic, antioxidant, nutraceutical, probiotic, and herbal therapies relating to the management of hepatobiliary disorders. Veterinary Clinics of North America: Small Animal Practice. 2004;34(1):67–172. PMID: 15032124. [See also: NTP Toxicology reports on BHA/BHT, pet food additive safety reviews.]