Cat Food and Diet

Unlike dogs, cats are carnivores that have evolved to a diet that is high in fat and protein and relatively low in carbohydrates. This does not mean that cats are unable to utilize plant proteins, only that they require certain amino acids and fatty acids that can only be found in meat of animal sources.
Some of the adaptations seen in cats resulting from a low carbohydrate (high fat and protein) diet include fewer taste buds and an inability to taste sweetness. Pancreatic and salivary gland amylase activity is relatively low when compared to the dog and an increase in dietary carbohydrates does not stimulate increased enzyme activity.

Protein Requirements

One of the key differences in the feline diet is the higher protein requirement over that of the canine. Cats require at least 2 grams of protein per pound of body weight per day. The relative dietary protein requirements of older vs. younger cats remains unknown. This higher requirement is not a result of a relatively higher demand for essential amino acids than that of the dog. Rather it seems the cat has evolved in a manner that has allowed its protein metabolic pathways to become less efficient or wasteful in the handling of dietary protein derived from protein-rich animal tissue sources.
Most feline pet foods provide protein levels in the range of 25-35% which represents 25-30% of the metabolizable energy (30 Kcal/lb/day), yet if the caloric density was lowered to 21 Kcal/lb/day, an increase to a 30% protein diet would be necessary.

Amino Acids in the Feline Diet

All cats require the amino acid taurine in their diet, unlike the dog. Diets deficient in taurine result in central retinal degeneration and blindness, as well as feline dilated cardiomyopathy.

Arginine is another essential amino acid in the cat (and is thought to be essential in the dog only during growth) and is an integral part of the urea cycle converting ammonia to urea. Lack of this amino acid results in kidney failure and rapid death.

Vitamin and Enzyme Requirements

Cats lack the enzyme delta 6 desaturase and so are unable to synthesize arachidonic acid from linoleic acid or to synthesize eicosapentanoic acid (EPA) from alpha-linoleic acid. Hence, cats must consume preformed arachidonic acid which is available only in animal fats and is not available in any plant products. Lack of arachidonic acid usually results in a variety of skin diseases.

Beta-carotene is only available in plants. However, cats lack the enzyme responsible for converting beta-carotene into retinol (Vitamin A). Deficiencies in Vitamin A lead to such problems as retinal degeneration, reproductive failure, and various forms of dermatitis.
The B vitamin niacin is converted from the amino acid tryptophane in dogs. However, cats are unable to use tryptophane as a precursor of niacin. Hence, more niacin is required in the feline diet. Deficiencies can lead to diarrhea, emaciation and death.