Cats meet their nutritional requirements by ingesting proteins, fats, carbohydrates, vitamins, minerals, and water just as people do. Proteins are essential substances for growth and repair of body tissues.
They cannot be synthesized in the body from dietary constituents other than protein. Therefore, they are extremely important to nutrition. Cats also use protein for energy. When used in this way proteins supply about 3.5 calories for each gram consumed. Unlike dogs and humans who can adapt to using carbohydrates or fats in place of protein to supply calories, domestic cats must always use a portion of the protein they eat for energy.
This is one important reason why cats must have diets high in protein. When well-balanced proteins supply at least 25% of the diet’s calories most cats’ needs will be met.
The minimum needed can range from 15% to 29% of calories depending on protein source and life stage. Proteins are composed of amino acids, and they vary widely in the kinds and proportions of amino acids present. Essential amino acids cannot be synthesized in the cat’s body and must be supplied by the diet in special proportions for optimum use. Proteins that supply the essential amino acids in nearly optimum quantities are given a high biological value because they are used most completely and efficiently by the body. Proteins with a high biological value are the best ones to feed and provide the best bases for commercial cat foods. Examples of such proteins are eggs, muscle meat, fish meal, and soybeans. In general, the higher the biological value the lower the actual requirement for the protein in the diet.
Cats, however, have requirements for certain amino acids that also influence exactly how much protein must be supplied. Taurine is the most notable essential amino acid for cats. One important use for it is for detoxification in their livers. Unlike dogs and other less carnivorous mammals, cats cannot synthesize enough taurine from other sulfur-containing amino acids to meet detoxification needs and maintain adequate body reserves. Taurine is found only in proteins of animal origin. Cats fed diets deficient in taurine develop retinal degeneration (feline central retinal degeneration, FCR) that causes reduced vision and dilated pupils, and may progress to complete blindness. Taurine deficiency may also induce a fatal heart muscle disease (feline dilated cardiomyopathy), immune system dysfunction, and blood clotting disorder. Kittens from taurine-deficient mothers are undersized, may die or grow slowly, and have abnormal skeleton and brain development resulting in impaired locomotion. Taurine levels are not adequate in plant products such as soybeans, normally considered valuable in formulating pet foods. The increased dietary fiber provided by plant products used in many commercial foods requires increased taurine intake, and heat processing of the food also reduces taurine levels. To avoid deficiency, foods for cats must contain a good source of animal protein and/or be supplemented with pure taurine. Never feed cats foods designed for dogs. Cats have become taurine deficient when fed cereal-based dog foods, and cats need on average at least twice as much protein as dogs. Eggs are an excellent source of protein (one egg = 7 g protein) of generally high biological value. They contain taurine, although less taurine than meat on an ounce-for-ounce basis. If you feed your cat eggs frequently, be sure they are cooked because raw egg white is not digested well. It also contains a substance called avidin that binds biotin, an important B vitamin, preventing its absorption from the gut. Additionally, raw eggs may contain Salmonella bacteria that may infect cats who eat raw eggs, causing illness and occasionally death. Milk and milk products such as cottage cheese or yogurt are high in protein, calcium, and phosphorous, but cannot provide complete protein for cats without the addition of taurine or in combination with meat, eggs, or fish. Many cats develop diarrhea when fed any milk products; others develop diarrhea only when fed large amounts. Diarrhea associated with the ingestion of milk products occurs when the lactose (milk sugar) in them is not digested. Undigested lactose promotes bacterial fermention and attracts water into the intestine, causing diarrhea. So provide milk and milk products as supplements to your cat’s diet with care. If loose stools develop when milk is fed, stop it immediately and wait for the stool to return to normal before trying new milk products. Cats who cannot drink milk without developing diarrhea can often eat cottage cheese, which has a much lower lactose content.
Fats provide the most concentrated source of energy (9 calories/g) of any of the necessary dietary components. They carry fat-soluble vitamins (D, E, A, K) and supply linoleic acid (linoleate) and arachidonic acid (arachidonate) that are essential to health in cats. Cats deficient in essential fatty acids grow poorly, have dry hair and dandruff, and may be listless and have increased susceptibility to infection. Diets lacking arachidonate will not support reproduction and adversely affect blood platelet function. Unlike dogs, cats cannot convert linoleate to arachidonate, a characteristic they share with other strictly carnivorous animals. Therefore, both linoleic acid (found in plant oils and animal fats) and arachidonic acid (found only in animal tissues) must be supplied preformed in the diet of the cat. A diet that derives about 2.5% of its calories from linoleic acid and at least 0.04% of its calories from arachidonic acid will provide adequate
levels of fatty acids and enough fat for absorption of the essential fatsoluble vitamins. Although diets higher in fat are not essential to cats’ health, cats are able to digest and metabolize fats extremely well, and very high-fat diets are not detrimental to them, providing proper levels of protein, vitamins, and minerals are also consumed. Moreover, fat (especially animal fat) increases the palatability of food to cats by affecting its texture (most important) and flavor. Cats generally prefer diets containing at least 15% fat as dry matter. Many commercial foods, especially dry and semimoist forms, provide lower fat levels. To improve palatability or supplement a diet you may think is fat deficient, add up to 1 tablespoon poultry fat, pork fat (lard), or corn oil for each 8-ounce (240 ml) measuring cup of dry or semimoist foods. Avoid hydrogenated coconut oils, as they can cause fatty liver disease in cats. Scaly skin and/or dry hair coat associated with inadequate levels of essential fatty acids should improve within one or two months after beginning supplementation. A better approach to treating unhealthy skin resulting from dietary deficiencies is to switch to commercial foods known to be nutritionally adequate and to discuss the problem with your veterinarian, since skin and coat problems are often caused by diseases not related to diet.
Carbohydrates (sugars, starches, and cellulose) are not required by cats in their diet. The digestible carbohydrates (sugars and starch), however, can be used as energy sources, providing 3.5 calories for each gram consumed. Cooking and/or fine grinding of carbohydrate sources (e.g., cereal grains, potatoes, vegetables) greatly improves their utilization and allows pet food manufacturers to formulate dry and semimoist foods based on these plant products that are not a major part of any cat’s natural diet. Products containing as much as 35% carbohydrate on a dry-matter basis can be utilized well and still provide room for adequate levels of other nutrients. Cellulose, an indigestible carbohydrate, is a source of dietary fiber. Fiber is not considered essential for simple stomached carnivorous mammals like domestic cats. Fiber-containing foods are useful, however, in preventing constipation in older cats with reduced intestinal function and to reduce the caloric density of diets for cats who tend to become fat when allowed to eat without restriction. Except for diets designed for special purposes such as weight reduction, diets for cats should contain no more than 5% fiber dry matter.