Cat food is food for consumption by cats. Cats have requirements for their specific dietary nutrients. Certain nutrients, including many vitamins and amino acids, are degraded by the temperatures, pressures and chemical treatments used during manufacture, and hence must be added after manufacture to avoid nutritional deficiency. The amino acid taurine, for example, which is found within meat, is degraded during processing, so synthetic taurine is normally added afterwards. Long-term taurine deficiency may result in retinal degeneration, loss of vision, and cardiac arrest.
The idea of preparing specialized food for cats came later than for dogs (see dog biscuits and dog food). This was likely due to the idea that cats could readily fend for themselves. In 1837, a French writer Mauny de Mornay critiqued this idea:
It is... thought wrongly that the cat, ill-fed, hunts better and takes more mice; this too is a grave error. The cat who is not given food is feeble and sickly; as soon as he has bitten into a mouse, he lies down to rest and sleep; while well fed, he is wide awake and satisfies his natural taste in chasing all that belongs to the rat family.
In 1844, another French writer expanded on this idea:
Normally in the country no care is taken of a cat's food, and he is left to live, it is said, from his hunting, but when he is hungry, he hunts the pantry's provisions far more than the mouse; because he does not pursue them and never watches them by need, but by instinct and attraction. And so, to neglect feeding a cat, is to render him at the same time useless and harmful, while with a few scraps regularly and properly given, the cat will never do any damage, and will render much service.
He goes on to say that it is all the more unreasonable to expect a cat to live from hunting in that cats take mice more for amusement than to eat: "A good cat takes many and eats few".
By 1876, Gordon Stables emphasized the need to give cats particular food:
If then, only for the sake of making (a cat) more valuable as a vermin-killer, she ought to have regular and sufficient food. A cat ought to be fed at least twice a day. Let her have a dish to herself, put down to her, and removed when the meal is finished. Experience is the best teacher as regards the quantity of a cat's food, and in quality let it be varied. Oatmeal porridge and milk, or white bread steeped in warm milk, to which a little sugar has been added, are both excellent breakfasts for puss; and for dinner she must have an allowance of flesh. Boiled lights are better for her than horse-meat, and occasionally let her have fish. Teach your cat to wait patiently till she is served—a spoiled cat is nearly as disagreeable as a spoiled child. If you want to have your cat nice and clean, treat her now and then to a square inch of fresh butter. It not only acts as a gentle laxative, but, the grease, combining in her mouth, with the alkalinity of her saliva, forms a kind of natural cat-soap, and you will see she will immediately commence washing herself, and become beautifully clean. (N.B.—If you wish to have a cat nicely done up for showing, touch her all over with a sponge dipped in fresh cream, when she licks herself the effect is wonderful.)