A cat carrying a house mouse

Cats are obligate carnivores: their physiology has evolved to efficiently process meat, and they have difficulty digesting plant matter.^[26] In contrast to omnivores such as rats, which only require about 4% protein in their diet, about 20% of a cat's diet must be protein.^[26] Cats are unusually dependent on a constant supply of theamino acid arginine, and a diet lacking arginine causes marked weight loss and can be rapidly fatal.^[86] Another unusual feature is that the cat also cannot produce the amino acid taurine, with taurine deficiency causing macular degeneration, where the cat's retina slowly degenerates, causing irreversible blindness.^[26] Since cats tend to eat all of their prey, they obtain minerals by digesting animal bones, and a diet composed only of meat may cause calciumdeficiency.^[26]

A cat's digestive tract is also adapted to meat eating, being much shorter than that of omnivores and having low levels of several of thedigestive enzymes that are needed to digest carbohydrates.^[87]These traits severely limits the cat's ability to digest and use plant-derived nutrients, as well as certain fatty acids.^[87] Despite the cat's meat-oriented physiology, several vegetarian or vegan cat foods have been marketed that are supplemented with chemically synthesizedtaurine and other nutrients, in attempts to produce a complete diet. However, some of these products still fail to provide all the nutrients that cats require,^[88] and diets containing no animal products pose the risk of causing severe nutritional deficiencies.^[89]