Animals that only eat meat and do not supplement it with another type of food, such as vegetation, are called obligate carnivores, and examples of obligate carnivores are the various species of cats. Other animals classified as obligate carnivores include hawks, eagles, snakes, lizards, crocodiles, mink, seals and walruses.
Obligate carnivores eat only meat because they are unable to digest vegetable matter and convert it into amino acids and vitamins. The only way they can obtain needed nutrients is through the flesh of animals they eat. Without a regular diet of meat, they die.
The digestive systems of cats, for example, are ideally evolved for raw flesh. Their digestive tracts are shorter than those of most other mammals. They do not need the fermenting bacteria to absorb plants or the ability to break down carbohydrates. The only time they ingest grain or other plant matter is when it is already within the stomachs of their prey. This accidentally acquired plant matter does not harm the cats, but if they do not get a high amount of protein in their diets, they begin to break down their own organs and muscles for nourishment. This is why cat owners are discouraged from buying cat foods high in vegetable content.