How to Care for a Healthy Cat: NUTRITION

The Classic Comprehensive Handbook of Cat Care


For many years little was known about the domestic cat’s nutritional requirements. Now, however, nutritional research has revealed that cats have distinctive nutrient needs that probably arose in concert with their development as true carnivores. Despite research efforts, minimum requirements for all the necessary food substances have not yet been well established for cats, so deciding exactly what is the most healthful diet for your cat’s growth, adulthood, and old age can be challenging.

In selecting the right foods for your pet keep in mind that external manifestations of nutritional deprivation may not appear until months or even years of feeding an inadequate diet have passed. Once present, the physical effects of poor nutrition often can never be reversed


  1. “As-fed basis.” This phrase refers to foods’ nutrient and moisture contents expressed as percentages. Normally, the percentages used refer to the amounts found in a pet food product as it comes directly from the can, bag, or box. However, the values for moisture will increase if water is added to the food, thereby diluting the other nutrients on an as-fed basis. Since the moisture content of foods can vary considerably (from about 5% to about 80%) comparison of nutrients present to a nutritional chart or between products becomes difficult unless the differing moisture levels are taken into consideration (see “dry-matter basis”). However, when choosing among products of the same general moisture content (e.g., between canned foods) there will be no problems if they are compared with one another on an as-fed basis. When adding foods or supplements to preformulated products, recommendations are often given on an as-fed basis in order to facilitate addition of the item (e.g., 1 teaspoonful per pound dry food as fed).
  2. “Dry-matter basis.” This phrase refers to the nutrient content of food expressed as a percentage of the food after all water is removed. For example, a food containing 20% protein and 50% water (moisture) on an as-fed basis will contain about 3 ounces (oz) (about 90 grams [g]) of protein in a pound (lb) (454 g). If all the water is removed, leaving 1/2 pound (227 g) dry matter, the amount of protein, 3 oz (90 g), per portion remains the same but the percentage expressed on a dry-matter basis increases to 40%. Expressing all nutrients on the same dry-matter basis (dry basis) makes comparison of different kinds of foods to one another and to charts of nutrient requirements easier. This is why requirements for certain vitamins, minerals, proteins, and fats are often expressed as a percentage of the dry matter of the food, i.e., on a dry basis (see chart). (To convert an amount of nutrient from an as-fed to a dry-matter basis, use the calculation).
  3. “As a percentage of calories.” The biological availability of certain nutrients, especially protein, is affected by calorie intake. In instances where the amount of a nutrient needed will be affected by the energy (calories) provided by the diet, nutrient content or requirements are often expressed as a percentage of calories provided by the diet. Although nutritionally correct, this concept is difficult for most people who are not professional nutritionists to apply, and information presented in this form is kept to a minimum in this book.
  4. “Per pound (or kiliogram) of body weight.” The simpliest, but sometimes less technically correct means to express the amount of any nutrient needed is to give the requirement as a unit per pound (or kilogram) of body weight. By convention, nutrients are expressed in various units such as international units (IU), milligrams (mg), or micrograms (µg).


  1. “Digestibility.” This is the relationship between the amount of a nutrient or food eaten and the amount absorbed expressed as a percentage. For example, a cat consuming a pound (454 g) of a food that is 80% digestible has only 12.8 oz (384 g) (16 oz [454 g] X 80%) available to the body for actual use. The difference in the two amounts represents the waste matter that is excreted.
  2. “Utilization.” This term expresses the relationship between the quantity of a nutrient or food eaten and the actual amount retained by the body. Like digestibility, the ratio is expressed as a percentage. Food utilization is the best overall way to determine the actual nutritional value of a food. Scientific analysis of food disposition in the body can provide this information. However, since food utilization figures are often not readily available to pet owners, food digestibility is often substituted for it in discussions of nutrition.
  3. “Metabolizable energy” (ME). This term represents the number of calories available to the body from food. It is conventional among nutritionists to specify nutrient concentration requirements for pet foods as quantities needed per each 1,000 calories of metabolizable energy (Kcal ME) provided by the food, since some nutrient requirements change when the calories available from a given quantity of food increase or decrease. When comparing calories provided by food to calories required by the animal, it is important to be sure that both are expressed in the same energy units. Metabolizable energy units specify the actual energy available. Other units such as gross energy or digestible energy are less accurate measures of the actual calories provided by food.


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 fat- soluble 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.


Cats require about 1 ounce (30 ml) of water per pound of body weight daily. They obtain this water in the food they eat and the liquids they drink. Water is also a by-product of metabolism; fat metabolism, in particular, is of great importance. The importance of foods in supplying the water requirements of cats is so great, in fact, that a cat on a moist food diet (which contains about 75% water) can easily be thought not to drink at all.

Cats on other diets, however, do drink frequently, and the actual amount of liquid a cat must drink daily is influenced by many factors in addition to diet, among them exercise, environmental temperature, and the presence of fever, vomiting, or diarrhea. Lactation also increases the required water intake. So the best solution to the problem of water intake is to be sure that your cat has access to clean water at all times. (Milk may be provided as an additional water source if it does not cause diarrhea.) Do not give your cat water considered unfit for human consumption, and, if for some reason you are unable to give your cat free water access, be sure to offer water at least three times a day.

A cat can go without food for days and lose 30% to 40% of his or her normal body weight without dying, but a water loss of 10% to 15% can be fatal. When cats stop eating (as they do frequently when sick) they must drink more water to make up for the decreased intake of food and in the amount provided by metabolism and for possible increases in need. To find out about providing water for your cat during illness.


Although the required levels of all the essential vitamins that should be included in cats’ diets have not been firmly established, many important facts about vitamins in the cat’s diet are known and should be heeded when selecting a diet for your pet. The table shows the currently recommended amounts of vitamins that should be fully available to a cat from his or her food. As with other nutrients, these levels will generally be lower than those actually present in commercial foods, since manufacturers must include higher levels when the food is formulated and first mixed to make up for nutrients that are not fully bioavailable from foods and losses caused by processing or storage.


Cats cannot convert beta carotene (found in green vegetables) to vitamin A as can dogs and people, so you must be sure that other sources of fully formed vitamin A (found in animal tissues) are provided in the diet to prevent a deficiency that can result in skin, eye, and reproductive changes. On the other hand, too much vitamin A in the diet can result in proliferative gingivitis, skeletal deformities, and crippling. In order to prevent vitamin A deficiency or excess, use a complete commercial cat food with vitamin A added as a basis for feeding and use liver, which is high in vitamin A, only as a supplement to your cat’s diet, not as a major part of it. Feed an average-sized adult cat no more than 1 ounce (30 g) of beef liver twice weekly. If necessary, balanced vitamin-mineral preparations may also be used as dietary supplements, but avoid giving unbalanced supplements such as cod liver oil to cats, since 1 teaspoonful can contain more than 5000 IU vitamin A. Use only balanced vitamin- mineral supplements recommended by your veterinarian and follow directions for their use carefully.


It is doubtful whether under normal feeding conditions vitamin E deficiency or excess will occur. There have been, however, many cases of vitamin E deficiency in cats because the need for vitamin E is significantly influenced by diet composition. Cases of vitamin E deficiency have resulted from an abnormal feeding practice considered normal by poorly informed owners: the feeding of excessive quantities of red meat tuna. It has also occasionally followed the feeding of other fish diets, fish oils (e.g., cod liver oil), or large quantities of liver.

Vitamin E deficiency results in oxidation of body fat and a generalized inflammation called pansteatitis (steatitis). Its signs include lack of appetite, fever, and pain accompanied by reluctance to move. It can eventually end in death. Vitamin E deficiency should be diagnosed and treated by a veterinarian, but, more important, you can prevent its occurrence. Use a complete commercial cat food as your cat’s basic diet and avoid frequent feeding of red meat tuna. Any tuna fed should be clearly marked—supplemented with vitamin E. Do not use fish oils (e.g., cod liver oil) as dietary supplements and feed liver only as previously recommended.


Cats have relatively high requirements for B vitamins in their diets. Foods for cats must contain at least twice the amounts of many B vitamins found in diets adequate for dogs—another good reason not to feed cats dog food. Several B vitamins are destroyed by heating, a process used in making commercial cat foods, so all good processed foods must be supplemented with B vitamins. One heat-sensitive B vitamin, thiamine, is also destroyed by enzymes found in certain raw fish and in raw soybeans.

Deficiency manifested by lack of appetite and neurologic disorders including seizures followed by weakness and death may develop in cats fed inadequately cooked fish or soy-based food and/or cooked products inadequately supplemented with thiamine.

Several B vitamins are synthesized by bacteria in the intestines of healthy cats. Intestinal problems, e.g., diarrhea, can eliminate this source, and antibiotics may also interfere with it. Vitamin supplementation is often necessary during prolonged illnesses involving the intestine or during
prolonged antibiotic treatment.


Although few studies have been done that establish the mineral requirements of cats, it seems unlikely that a cat who eats a diet well balanced in other respects would become deficient in minerals.

Unsuspecting cat owners can more easily provide improper rather than inadequate mineral supplies for their pets, since the relationship among the various minerals in the diet is as important as deficiency or excess. A good example of this problem is the interrelationship among the minerals calcium and phosphorus and vitamin D. These relationships are often upset by oversupplementation and/or by catering to a cat’s food preferences instead of his or her needs.


Calcium and phosphorus should be present in the diet of cats in a ratio of about 1 to 1. If an adequate amount of each of these minerals is present but the ratio is incorrect, abnormal mineralization of bone occurs in the growing kitten and in the adult cat as well. If adequate amounts of calcium and phosphorus in the proper ratio are provided but without sufficient vitamin D, abnormalities of bone result again. Insufficient levels of vitamin D interfere with calcium absorption in the intestine. Excessive amounts of vitamin D in the presence of adequate levels of calcium and phosphorus may result in excessive mineralization of bone, abnormal teeth, and calcification of the soft tissues of the body. The delicacy of these relationships is remarkable.

Unthinking or uninformed owners most often distort the calcium- phosphorus balance of their cat’s diet by feeding a diet consisting almost exclusively of muscle meat or organ meats such as liver, heart, or kidney.

All of these meats contain phosphorus but are devoid of calcium, which results in a calcium-phosphorus ratio of 1 to 15 or greater. Prolonged feeding of such a diet results in severe demineralization of bones, pain, and sometimes fractures or paralysis, a condition called nutritional secondary hyperparathyroidism. An adult cat may exist on such a diet for years without showing signs of disease, but the body changes are occurring nevertheless. A cat’s requirement for vitamin D is low, so that health problems relating to this nutrient are best avoided by preventing oversupplementation. Remember that the wild ancestors and living relatives of the domestic cat relied on a variety of foods. Follow the dietary recommendations set out previously and on the following pages and/or follow the advice of a knowledgeable veterinarian to prevent nutrition- induced disease in your cat.