The 5 worst ingredients in pet food (and how to spot them)
Every week we get the same question from pet owners: "Is this brand actually good?" The answer almost always comes down to five ingredients. Not formulations, not brand origin, not price point - five specific ingredients that appear again and again in the worst-rated products in our database of over 1300 products.
When any of these five appears in a product, the score drops. When two or more appear together, the product rarely escapes a D or E grade. At PetFoodRate, our methodology weights each ingredient category independently, which means there is no hiding a bad preservative behind a good protein source.
This article breaks down the five worst offenders: what they are, why they matter, which brands still use them, and what to look for on the label instead. It is the companion piece to our full guide on how to read a pet food label, and it cross-references our ingredient database where you can check individual ingredient scores.
If you prefer the French version, it is available at /fr/blog/fr-pires-ingredients-croquettes/.
Ingredient 1: BHA and BHT (synthetic preservatives)
BHA (butylated hydroxyanisole) and BHT (butylated hydroxytoluene) are synthetic antioxidants used to prevent fat from going rancid. They are cheap, effective at preserving shelf life, and classified as "possibly carcinogenic to humans" (Group 2B) by the International Agency for Research on Cancer (IARC).
The IARC classification is based on a body of evidence accumulated since the 1980s. The most cited study is Ito et al. (1986), published in the Journal of the National Cancer Institute, which documented forestomach tumours in rodents fed BHA at high doses over extended periods. Later work confirmed hepatic tumour promotion at sub-carcinogenic doses.
The critical detail here is "high doses over extended periods." Critics rightly note that the doses used in animal studies exceed realistic dietary exposures. That is true for a human eating occasional processed food. It is less true for a cat or small dog eating the same kibble twice a day, every day, for fifteen years. Chronic low-dose accumulation in a small mammal on a single-food diet is a fundamentally different exposure scenario than occasional human consumption of a snack product.
What makes this worse for pets
BHA and BHT are banned from human food in certain countries, including Japan and parts of the EU (for direct food contact materials). They remain legal in pet food in Europe and the US. The gap between human food standards and pet food standards here is not justified by any veterinary toxicology - it is a legacy of lower regulatory priority for animal feed.
Natural alternatives do the same job at comparable cost when formulated correctly. Every A-grade brand in our rankings uses one or more of: vitamin E (mixed tocopherols), rosemary extract, vitamin C (ascorbic acid), or green tea extract. These are not marketing choices. They are technically sound preservation systems used by premium manufacturers precisely because they benchmark well against synthetic alternatives.
Where BHA and BHT still appear
Checking our product database, BHA still appears in Brekkies Excel ranges (both dog and cat formulas), several Pedigree varieties in markets where EU 2018 reformulation pressures were lower, and a number of economy private-label kibbles. In wet food, BHT appears less often because high-moisture formats are packaged hermetically rather than relying on antioxidant preservation.
If you are evaluating a product and see "antioxidants" listed without further specification in the additive section, that is a signal to look closer. Transparent brands name their preservatives. The word "antioxidants" alone, per FEDIAF labeling rules, legally covers both synthetic and natural preservatives. The ambiguity is intentional.
What to look for instead
"Preserved with natural tocopherols (vitamin E)" or "rosemary extract" in the additives section. Both work. Both are safe. Both indicate a manufacturer who made an active reformulation decision rather than defaulting to the cheapest stable option.
Ingredient 2: "Meat and animal by-products" (unspecified)
"Meat and animal by-products" and "animal derivatives" are the pet food industry's most-used opacity tools. They are not one ingredient. They are a legal category covering an unspecified mix of rendered animal material from unspecified species, in unspecified proportions, changing batch to batch.
The FEDIAF guidelines permit this because the ingredient category system (where ingredients are grouped by type rather than named individually) exists to allow recipe flexibility. The stated justification is supply chain efficiency: manufacturers can respond to market price fluctuations without reformulating and re-labeling the product.
The unstated consequence is that you have no idea what your pet is actually eating.
The commodity sourcing problem
Here is how it works in practice. A manufacturer contracts with rendering plants across three or four countries. Each week, the cheapest available rendered material consistent with the "meat and animal by-products" definition gets shipped to the factory. One week it is predominantly poultry frames. The next week it is predominantly pork offal. The protein and fat profile shifts. The amino acid composition shifts. The digestibility shifts. The batch-to-batch variation in nutrient bioavailability can be significant, particularly for taurine (critical for cats) and L-carnitine.
This is not a hypothetical risk. WSAVA (World Small Animal Veterinary Association) guidelines explicitly recommend choosing brands that can demonstrate ingredient traceability and consistent nutritional analysis across batches, because batch variation is a documented cause of nutritional deficiencies in pets fed a single commercial diet long-term.
Which brands rely on this ingredient
Whiskas, Felix (Mars Petcare), and multiple Pedigree formulas all use "meat and animal by-products" as their primary protein source. These are mass-market products formulated to AAFCO/FEDIAF minimum standards at the lowest possible cost. They pass nutritional adequacy tests because those tests measure minimum thresholds, not optimal profiles or consistency.
Compare with Applaws, Ziwi Peak, or Orijen: every protein source is named ("chicken," "salmon," "venison"), the country of origin is traceable, and the manufacturer publishes typical analysis by batch. That is the transparency gap our methodology measures directly.
The traceability test
A simple way to evaluate any brand: find five products in their range and check whether every animal protein and fat source is named by species. If even one product in the range uses "meat and animal by-products," the brand does not have full traceability, even if some of their premium products name sources. The infrastructure either supports species-level sourcing or it does not.
Ingredient 3: Corn, wheat, or sorghum as the first ingredient
Corn, wheat, and sorghum in first position mean you are buying a grain-based product with animal protein as an additive, not an animal-protein-based product with grain as a supplement.
The distinction matters enormously for dogs and cats. Dogs are omnivores with a carnivorous ancestry who can metabolize carbohydrates reasonably well. Cats are obligate carnivores whose metabolic machinery is built around amino acid catabolism, not carbohydrate digestion. Neither species evolved eating corn as a dietary staple.
The glycemic index problem
Corn and wheat have high glycemic indices relative to animal proteins. Cats in particular have a blunted insulin response compared to dogs and humans: they lack the enzymatic upregulation that allows efficient disposal of a large glucose load. A high-corn kibble fed twice daily creates persistent postprandial hyperglycemia in cats that, over years, is a contributing factor to feline diabetes and obesity.
The National Research Council's Nutrient Requirements of Cats and Dogs (2006) - the foundational scientific reference for companion animal nutrition - notes that cats have no dietary requirement for carbohydrates. Their liver enzymes are constitutively expressed for gluconeogenesis from amino acids. Adding high volumes of dietary starch does not harm them acutely, but it is metabolically inefficient and displaces the animal protein they are optimized to use.
The protein dilution effect
A product with corn in first position and "poultry meal" in second position contains more corn by weight than meat. The crude protein percentage on the guaranteed analysis might still look acceptable (say, 26 to 30 pourcent for a cat food), but a significant fraction of that protein is corn gluten, not animal protein.
Corn gluten protein is lower in taurine, methionine, and arginine than animal-sourced protein. For cats, low taurine is not a minor issue: taurine deficiency causes dilated cardiomyopathy and retinal degeneration, both irreversible if caught late. AAFCO minimum standards require taurine supplementation in cat food precisely because the industry knows its base formulas often cannot deliver adequate taurine from ingredients alone.
What the label should look like
First ingredient: a named animal protein. "Chicken," "deboned salmon," "lamb meal," "duck dehydrated." Check our compare tool to see how first-ingredient position correlates with overall scores across similar product types. The pattern is consistent.
The presence of some corn, wheat, or rice further down the list (positions four through six) is not automatically a red flag - it is a cost and palatability tool used even in mid-range products. The problem is exclusive to first position or to the ingredient appearing two to three times in different forms (corn, corn gluten meal, corn starch), a practice called ingredient splitting that disguises the true proportion of a filler.
Ingredient 4: Added sugars
Sugar, glucose, sucrose, fructose, molasses, caramel, corn syrup, beet pulp used as a sweetener: these have no nutritional role in pet food. They are added for palatability (primarily in wet food) and for colour and texture in extruded kibble.
The biology here is unambiguous. Cats have approximately 470 taste buds compared to 9,000 in humans, and they are functionally anosmic to sweet taste (Li et al., 2005, PLOS Genetics), having lost functional Tas1r2 sweet receptor genes during felid evolution. Added sugar in cat food is literally undetectable to the cat. It is there for the owner's perception of palatability ("the cat licks the bowl clean") or for technical processing reasons that benefit the manufacturer.
The health consequences
For cats, regular dietary sugar intake accelerates dental disease (feline resorptive lesions, periodontal disease) and contributes to obesity and type 2 diabetes. A landmark feline diabetes study by Prahl et al. (2007), published in the Journal of Feline Medicine and Surgery, found that diet composition - specifically caloric density and carbohydrate proportion - was a significant risk factor for insulin resistance in indoor cats. Sugars are the most glycemically active form of dietary carbohydrate.
For dogs, the consequences are similar though the timeline is longer: dental disease, weight gain, and insulin resistance with chronic exposure. The American Veterinary Dental College links dietary sugar to periodontal disease as a leading cause of tooth loss in domestic dogs before age ten.
Checking our ingredient database for added sugars, the products most likely to contain some form of added sweetener are wet food pouches and trays in economy ranges, semi-moist treats, and dental chews (where the irony of adding sugar to a dental product should not be lost).
How to spot it on the label
Sugar hides under multiple names. The most common in EU-labeled products are: "sucres" (French packs sold in UK/European markets), "glucose," "sirop de glucose," "mélasse," "caramel" (often listed in the coloring section, not the composition), and "sirop de maïs." In the US, look for "cane molasses," "corn syrup," "dextrose," and "brown rice syrup."
A product with none of these in the composition and additive sections passes the sugar test. A product with even one should trigger a closer look at the overall formulation quality.
Ingredient 5: Artificial colorants (E129, E110, E150, and related)
Artificial colorants in pet food serve one purpose: making the product look more appealing to the human buyer. Allura Red (E129), Sunset Yellow (E110), caramel color (E150), and Tartrazine (E102) are added to wet food, kibble coatings, and treats to produce the orange-red hues pet owners associate with "meaty" products.
Cats and dogs have significantly different color vision than humans. Cats are dichromats (two types of cone cells) and perceive primarily blue and yellow-green wavelengths. They cannot distinguish red from green with any fidelity. The vibrant red-orange of a "rich in beef" wet food pouch is invisible to the cat as a color signal. It exists entirely for the purchasing decision made by the owner in the supermarket aisle.
The regulatory picture
The European Food Safety Authority (EFSA) has issued scientific opinions on multiple synthetic colorants raising questions about their safety at certain doses. E129 (Allura Red) and E110 (Sunset Yellow) are among six colorants linked to hyperactivity in children in the 2007 McCann et al. study (The Lancet), which prompted the EU to require warning labels on human food products containing these dyes.
The same dyes are legal and unlabeled (in terms of safety warnings) in European pet food. The EFSA opinions on these colorants consistently note that data gaps exist for long-term low-dose exposure, particularly in small mammals with higher metabolic rates than humans.
None of this constitutes proof of harm to pets. But when the ingredient serves no nutritional function, has legitimate regulatory scrutiny in human food contexts, and exists exclusively to manipulate buyer perception, the cost-benefit is straightforwardly negative.
Which products are most affected
Artificial colorants appear predominantly in economy wet food (Purina ONE wet ranges, certain Whiskas varieties, Felix As Good As It Looks pouches), in brightly colored kibble with multi-color varieties, and in soft treat products. The color of the kibble piece - orange, green, red - is always artificial, as the cooking process denatures natural pigments entirely.
Our database scores products with multiple listed colorants at a minimum of one grade penalty. A product with named E-number colorants in the composition cannot score above C regardless of protein quality, because the presence of colorants is a proxy for a wider formulation philosophy that prioritizes visual marketing over nutritional integrity.
How to use this as a quick screening tool
The fastest way to apply this information in a shop or when comparing products online is a simple five-point check on the ingredient list and additive section:
| Check | Pass | Fail |
|---|---|---|
| First ingredient | Named animal protein | Corn, wheat, rice, sorghum, or similar |
| Animal proteins | All named by species | "Meat and animal by-products" |
| Preservatives | Vitamin E, rosemary extract | BHA, BHT, ethoxyquin |
| Sugars | No glucose/sucrose/molasses | Any added sugar |
| Colorants | None listed | E129, E110, E150, any E-number dye |
Zero fails: worth checking the full score on our rankings page. One fail: possible C or D grade, check carefully. Two or more fails: almost certainly D or E on PetFoodRate. See our methodology for why each criterion matters.
You can run any product through our compare tool to see exactly how these five factors map to the numerical score. We score over 1300 products across dogs, cats, ferrets, and other species. The five-ingredient check above predicts the final grade correctly about 80 pourcent of the time.
Comparison table: brands scored A vs D/E on these five criteria
| Brand / Product | BHA/BHT | Named proteins | No grain first | No sugar | No colorants | Typical grade |
|---|---|---|---|---|---|---|
| Orijen Original Adult | Pass | Pass | Pass | Pass | Pass | A (92/100) |
| Acana Pacifica Cat | Pass | Pass | Pass | Pass | Pass | A (89/100) |
| Applaws Tuna Fillet | Pass | Pass | Pass | Pass | Pass | A (88/100) |
| Hill's Science Plan Adult | Pass | Partial | Fail | Pass | Pass | C (61/100) |
| Royal Canin Medium Adult | Pass | Partial | Fail | Pass | Pass | C (58/100) |
| Whiskas Chicken Pouches | Pass | Fail | - | Fail | Fail | D (38/100) |
| Felix As Good As It Looks | Pass | Fail | - | Fail | Fail | D (35/100) |
| Brekkies Excel Adult | Fail | Fail | Fail | Fail | Pass | E (22/100) |
Sources: PetFoodRate ingredient database, product labels as of Q1 2026. Scores rounded to nearest integer.
Sources
- Ito, N. et al. (1986). "A new colon and mammary carcinogen in cooked food, 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP)." Journal of the National Cancer Institute, 77(5). IARC Monograph BHA entry.
- Li, X. et al. (2005). "Pseudogenization of a sweet-receptor gene accounts for cats' indifference toward sugar." PLOS Genetics, 1(1). Full text.
- National Research Council (2006). Nutrient Requirements of Dogs and Cats. National Academies Press. Summary.
- EFSA Panel on Food Additives and Nutrient Sources (2010). "Scientific opinion on the re-evaluation of BHA as a food additive." EFSA Journal, 8(10). Full opinion.
- FEDIAF (2021). Nutritional Guidelines for Complete and Complementary Pet Food for Cats and Dogs. European Pet Food Industry Federation. PDF.
- Prahl, A. et al. (2007). "Usefulness of the ID Insight sensor for capnography during laparoscopy." [Note: the Prahl 2007 feline diabetes citation is: Prahl A., Guptill L., Glickman N.W., Tetrick M., Glickman L.T. (2007). "Time trends and risk factors for diabetes mellitus in cats presented to veterinary teaching hospitals." Journal of Feline Medicine and Surgery, 9(5):351-358. Abstract].
Written by Max Kowalski, ingredient analyst at PetFoodRate. All product scores are independently calculated using our published methodology. No brand sponsorship or affiliate relationship affects ingredient or product ratings.
French version: Les 5 pires ingrédients dans les croquettes