Long-form

Why Your Cat Cannot Just Eat Anything

What peer-reviewed research tells us about feline obligate carnivory, and why cats have nutritional needs that dogs and humans do not.

Published April 2026

You will hear it said that cats are carnivores. What you will hear less often is exactly what that means at a biological level, and why it matters when you are choosing between cat foods on a shelf.

We looked at the peer-reviewed research behind feline nutrition. Published studies from geneticists, nutritional ecologists, and veterinary scientists. Here is what the science actually says.

They Are Built Differently

In 2014, a team led by researchers at Washington University analysed the domestic cat genome, building on the first draft sequenced in 2007. Comparing it against dog, cow, tiger, and human genomes, they found that cats carry positively selected genes for lipid metabolism that evolved specifically to support a meat-based diet. These genes allow cats to efficiently break down the high levels of fat found in animal prey. The same genetic changes were not found in cows or humans, who eat more varied diets and would not need them.

The same study found that the genomic differences between domestic cats and wildcats are remarkably small. The signatures of domestication in cats are concentrated in genes affecting memory and reward learning, not dietary adaptation. Cats became comfortable around humans. Their digestive biology stayed the same. [1]

They Did Not Change When We Domesticated Them

A 2017 study in Nature Ecology and Evolution analysed ancient DNA from 352 archaeological cat remains spanning thousands of years. It confirmed that cats were never selectively bred for dietary changes the way dogs were. Wildcats are solitary, territorial hunters with no social hierarchy, which makes them poor candidates for traditional domestication. Instead, cats entered a commensal relationship with early farmers around 9,000 years ago, hanging around grain stores to hunt rodents.

Directed breeding of cats only began after the Middle Ages. Even coat colour variation did not appear at high frequency until then. The domestic cat is, genetically speaking, still a wild predator that tolerates living in your house. [2]

They Regulate What They Eat

If cats are obligate carnivores, do they actually behave like it when given a choice? Yes.

A series of studies conducted at the WALTHAM Centre for Pet Nutrition, in collaboration with nutritional ecologists at the University of Sydney and Massey University, tested what happens when you give cats free access to foods with different protein, fat, and carbohydrate ratios. Across multiple experiments using both wet and dry foods in various combinations, cats consistently selected a diet of approximately 52% protein, 36% fat, and 12% carbohydrate by energy.

More importantly, the researchers identified what they called a "carbohydrate ceiling." Cats would stop eating rather than consume more than about 20 grams of carbohydrate per day. When only high-carbohydrate foods were available, cats ate less overall, leaving themselves short on protein and fat rather than exceeding their carbohydrate limit.

This target closely matched the estimated natural diet of free-ranging feral cats, suggesting that domestic cats have retained the capacity to regulate macronutrient intake to match the diet of their wild ancestors, even when the foods available look nothing like a mouse. [3][4]

We ran every product in our database through this framework, converting guaranteed analysis values into energy percentages using modified Atwater factors. Of the 100 products with sufficient data, the closest match to the 52/36/12 target is Purina Pro Plan Adult Chicken in Gravy, at 54.6% protein, 32.9% fat, and 12.5% carbohydrate by energy. It is a Nestle Purina wet food, not a product of Mars Petcare, whose WALTHAM researchers conducted these studies. Almost no other product comes within 20 points of the target. Most kibble runs double the carbohydrate ceiling. Most wet food overshoots protein and undershoots fat.

This does not invalidate the research. The methodology is sound and the findings have been independently cited hundreds of times. We flag the funding behind it for transparency: these studies were run by the WALTHAM Centre for Pet Nutrition, owned by Mars Petcare. The 52/36/12 target they produced is one almost no commercial cat food meets, Mars-owned products included.

They Cannot Handle Sugar

Cats process different carbohydrates very differently. A 1994 study by Ellen Kienzle at the University of Munich tested how cats responded to diets containing starch, sucrose, glucose, galactose, and lactose.

Cooked starch at moderate levels (29 to 37% of dry matter) did not significantly change blood sugar compared to a carbohydrate-free control diet. Starch in kibble, properly cooked, does not cause blood sugar spikes in cats.

Simple sugars were a different story. Pure glucose caused a steep rise in blood sugar within one hour. Sucrose caused mild but persistent hyperglycaemia. Galactose caused persistent low blood sugar and significant galactose buildup in the bloodstream.

The most striking finding involved what appeared in the cats' urine. Cats fed starch or the carbohydrate-free control had virtually no sugar in their urine. Every group fed simple sugars showed glucosuria, meaning the sugars were passing through the kidneys unmetabolised. The galactose group excreted extreme levels. Kienzle concluded that cats have a rather limited capacity to metabolise sugars.

This is why KibbleGuide flags added sugars in red across the site. They serve no nutritional purpose for cats, and the evidence shows cats cannot process them properly. [5]

The Risk of Unsupplemented Meat Diets

If cats need meat, surely an all-meat diet is ideal? Not necessarily.

A case report from the University of Zurich documented six cats diagnosed with nutritional secondary hyperparathyroidism, a condition caused by calcium deficiency. The cats had been fed unsupplemented meat diets, which are high in phosphorus but very low in calcium. The result was severe bone loss. Five cats had spontaneous fractures of long bones, pelvis, or spine. Four showed seizures or muscle twitching from low blood calcium. Two had to be euthanised because of irreversible spinal damage.

The four surviving cats recovered with nothing more than a switch to a nutritionally complete diet and cage rest.

Meat alone does not provide everything a cat needs. A complete diet requires the right balance of calcium, phosphorus, taurine, vitamin A, and other nutrients that cats cannot synthesise on their own. This is what the "complete and balanced" statement on commercial cat food packaging is supposed to guarantee. [6]

What This Means for Choosing Cat Food

None of this research tells you which brand to buy. That is not what KibbleGuide does either. But it does give you a framework for understanding what to look for.

Protein source matters because cats are genetically adapted to derive their energy from animal fat and protein, not carbohydrates [1]. Carbohydrate content matters because cats have a biological ceiling for how much they will consume, and high-carbohydrate foods can leave them short on the nutrients they actually need [3][4]. Added sugars are a concern because cats literally cannot metabolise them properly [5]. And nutritional completeness matters because even the highest quality single ingredient, fed alone, can cause serious harm [6].

The ingredient list on a cat food label is the starting point, not the whole picture. But it is a starting point that most brands make unnecessarily difficult to interpret. That is what we are here to help with.

Sources

[1] Montague, M.J. et al. (2014). Comparative analysis of the domestic cat genome reveals genetic signatures underlying feline biology and domestication. Proceedings of the National Academy of Sciences, 111(48): 17230-17235.

[2] Ottoni, C. et al. (2017). The palaeogenetics of cat dispersal in the ancient world. Nature Ecology and Evolution, 1: 0139.

[3] Hewson-Hughes, A.K. et al. (2011). Geometric analysis of macronutrient selection in the adult domestic cat, Felis catus. Journal of Experimental Biology, 214(6): 1039-1051.

[4] Hewson-Hughes, A.K. et al. (2013). Consistent proportional macronutrient intake selected by adult domestic cats despite variations in macronutrient and moisture content of foods offered. Journal of Comparative Physiology B, 183: 525-536.

[5] Kienzle, E. (1994). Blood sugar levels and renal sugar excretion after the intake of high carbohydrate diets in cats. Journal of Nutrition, 124(12 Suppl): 2563S-2567S.

[6] Tomsa, K. et al. (1999). Nutritional secondary hyperparathyroidism in six cats. Journal of Small Animal Practice, 40(11): 533-539.

[3][4] were conducted at the WALTHAM Centre for Pet Nutrition (Mars Petcare) with independent academic collaborators from the University of Sydney and Massey University. Conflict of interest noted per KibbleGuide editorial standards. All other authors: no industry affiliations identified.