Arguably domestic cat are overspecialised eaters. They are ‘hypercarnivores’. Their dietary requirement are too inflexible and demanding. They are “stuck firmly in the nutritional dead end their ancestors bequeathed to them” (Dr John Bradshaw in Cat Sense). If only cats had evolved like dogs in respect of diet they might have been more successful. Cats are carnivores out of necessity because of their extreme dietary requirements. Dogs are classified as carnivores but they are actually omnivores like foxes and bears. Millions of years ago the evolution of the cat resulted in this specialised diet and now domestic cats are stuck with it.
Cats cannot taste sugars because their taste buds evolved to focus on meat eating. This resulted in cats being sensitive to the sweetness or bitterness in the flesh of their prey. I had never thought of meat being sweet or bitter. Presumably cats like sweet meat but perhaps this is not a conventional concept of sweetness. Perhaps ‘sweet’ means ‘less bitter’.
Cats require much more protein than humans or dogs. This is because they obtain most of their energy from protein in flesh rather than carbohydrates (highlighting the inherent inadequacy of dry cat food). Cats cannot use the protein in their diet to repair and maintain their bodies as other animals can. And cats need protein which contains the amino acid taurine. Further this ‘component’ does not occur naturally in cats as it does in humans.
Cats cannot make a type of hormone called prostaglandins from plants as most other mammals can. They have to rely on fats from animals which they can digest and metabolise.
The vitamin requirements of cats are more demanding than ours. They need vitamin A and vitamin D but cannot convert sunshine to vitamin D as we can and they need a lot of B vitamins, niacin and thiamine.
The cat needs a lot of meat to meet these demands and fish contains an enzyme which destroys thiamine when eaten to excess. It is nearly impossible to try and meet these dietary requirements through a vegetarian diet which is why it is rarely attempted.
The domestic cat is a good ship’s animal hence the well-known ship’s cat. Cats don’t require vitamin C which is an important nutrient for sailors to combat scurvy. Also cats have very efficient kidneys; they drink very little water, a useful attribute on board a ship where fruit and water is limited.