From the cat's point of view, what is the sense in wasting energy synthesizing certain substances within its body when a steady diet of prey can readily supply those substances? And why should a cat's body work to conserve protein when a prey diet provides the cat with abundant protein? The evolutionary consequence of this one-step approach to dining is the modern cat's dependence on an animal diet to meet its nutritional needs.

The Food Tree Food provides the cat with nutrients -- proteins, carbohydrates, fats, minerals, vitamins, and water -- that are crucial to the growth, reproductive, and adult stages of the animal's life cycle. Nutrients are responsible for building tissue; supporting chemical reactions; transporting substances in, around, and out of the body; and influencing and animal's acceptance of its food. In addition, protein, carbohydrates, and especially fats supply the energy that fuels these life-sustaining processes. Proteins -- organic compounds consisting of amino acids linked together -- are the building blocks of the body. The body uses various combinations of the approximately 20 amino acids to create proteins. Some of these are nonessential amino acids manufactured within the cat's body; others are essential amino acids that the cat's diet must provide. (All of the amino acids, however, are necessary. The distinction between nonessential and essential is that the latter must be supplied in the diet). One such amino acid in the cat is taurine. Taurine deficiency in cats causes reproductive problems, blindness, and heart disease. Arginine is another essential amino acid. An arginine-deficient diet leads to a situation in which the cat develops toxicosis because it can't adequately convert the harmful waste product ammonia into urea (normally eliminated via the urinary system). Fortunately, there is a simple strategy for avoiding the dangers of taurine and arginine deficiencies in cats: make sure your cat's diet contains adequate amounts of these and other essential amino acids. A cat's protein requirement varies according to its life stage. A healthy adult cat's diet should contain 30 to 45 percent protein on a dry-matter basis (without the water content of the food). During the more ''protein needy'' growth and reproductive stage of an animal's life, animal nutritionists recommend 35 to 50 percent protein on a dry-matter basis. Because cats have a higher protein requirement than dogs, you should never food dog food to your cat. Don't feed your cat a vegetarian diet either. Because cats are obligate carnivores, they lack many of the enzymes needed to create certain nutrients. These nutrients include some that are not found in vegetable matter; hence, a vegetarian diet is not nutritionally adequate for cats. We recommend you buy cat food that lists meat-based protein high on the ingredient list on the label. Carbohydrates provide energy and bulk. Strictly speaking, cats probably don't require carbohydrates in their diet. However, most cat-food manufacturers include carbohydrates in their products. Cats do require dietary fat to supply essential fatty acids (used in many body processes) and to transport fat-soluble vitamins around the body. Dietary fat is also an important source of energy. A healthy adult cat's diet should contain no less than 10 percent (and no more than 30 percent) fat on a dry-matter basis. Kittens should have no less than 18 percent and no more than 35 percent fat on a dry-matter basis. Like the diet of other animals, a cat's diet must also supply vitamins. But an unusual characteristic of cats is that they cannot form vitamin A from beta-carotene. Cats are also inefficient at converting the amino acid trypophan into the vitamin niacin. However, we caution owners not to add vitamin or mineral supplements to their feline companion's food without first consulting animal nutritionist. Indeed, veterinarians see more problems caused by owners who overzealously supplement with vitamins and minerals than by vitamin and mineral deficiencies. A quality cat food from a reputable manufacturer contains adequate dietary vitamins and minerals. (Homemade diets may not). Water -- vital to all life processes -- is a nutritional necessity. A cat might survive a loss of up to 50 percent of its overall weight. But if it loses just 15 percent of its water weight, it will die. (Be especially attentive to a cat that has a severe bout of vomiting or diarrhea. It is in danger of dehydrating and should be promptly taken to the animal hospital). Although all commercial cat food has some degree of moisture depending on the type of food (dry food has 6 to 10 percent; canned food can have up to 78 percent by law), make sure your cat has access to plenty of fresh water at all times.

Palatability Factors
Although all cats have common nutritional requirements, each cat is an individual with its own particular gastronomic fancies. Studies of cats' eating behavior have revealed that several factors -- such as how a food smells, how it tastes, how it feels, and how warm it is -- influence what a cat will or will not eat. The feline sense of smell (olfaction) is more developed than the human sense of smell. (Cat brains dedicate a relatively larger area to processing scent information than ours do). Smell, therefore, along with taste, plays a major role in shaping a cat's food preferences. In one study, cats initially ate more of a bland diet when researchers blew the smell of cooked rabbit over the food than when they blew air over the food. (This effect, however, diminished over time). The important role smell can play in stimulating appetite probably explains why a sick cat that cannot breathe through its stuffy nose is less inclined to eat. If you are encouraging a sick cat to eat, try enhancing the smell of its food. The loss of odor and change of texture that occurs as moist canned food dries out may explain why cats sometime leave half of it uneaten in their dishes. After smell, comes taste. Taste buds, located on the cat's tongue, respond, or course, to food. Because cats are carnivorous, their sense of taste is geared to respond to the taste of meat. In terms of flavor, cats prefer salty, sour, or bitter-tasting substances. We also know that cats don't develop a sweet tooth because they have no perception of simple sugars. How a feed ''feels'' is also important to cats. Although most cats prefer canned food, many cats prefer dry. Choice of texture comes down to the preference of the individual cat. Given their druthers, most cats would rather not eat food directly from the freezer; they prefer food that is close to their own body temperature. (This may stem from the fact that cats in the wild eat warm prey). Ultimately, your cat will decide on its own ''yum yum'' preferences and eat what it darn well pleases!

The Perfect Cat Food
One of the questions owners most frequently ask their veterinarians is ''What should I feed my cat?'' There is no single definitive answer. Products change over time and so may your cat's preferences and nutritional needs. What is important is to feed your cat a balanced diet that meets its nutritional needs at that particular time in its life cycle. We don't recommend homemade diets. Given the complexity of feline nutritional needs, it is difficult and time-consuming to create and sustain a nutritionally adequate homemade diet. But if you are set -- as some of you are -- on making your cat's food, make sure you have an animal nut5ritionalist review your recipe. Fortunately, many quality commercial products are now available. They come primarily in two forms -- dry kibble and moist canned food. One form is not nutritionally superior to the other, so the form you choose will depend on your life style and your cat's preference. Neither is there any intrinsic advantage of free-choice (ad libitum) feeding over meal feeding. Again, it depends on your circumstances. (For a cat with a tendency toward plumpness, however, free-choice feeding is probably not the way to go). Finding a suitable product for your cat may take some effort. Ignore the marketing hype and learn to decipher the information on the cat-food label. Above all, make sure a particular product is nutritionally adequate for your cat before you buy it. Does it contain proteins, fasts, minerals, and vitamins in sufficient (but not excessive) amounts? Does the product supply your cat with the essential substances it cannot manufacture for itself? Has the product been tested using feeding trials on actual cans? If you have questions about your cat's needs, consult with your veterinarian or an animal nutritionist. If you have concerns about a product, call the pet-food manufacturer. And if you have any doubts, don't buy the product. Admittedly, investigating the pros and cons of different cat foods takes some effort, but given the special nature of the cat's dietary needs, it's time well spent.

Milk Intolerance
In spite of the customary image of a cat with its face in a dish of cream, cats must acquire a taste for dairy products. Although some cats obviously enjoy cow's milk, many cats do not. It's important to remember that cow's milk differs from the milk kittens get from their nursing mother. Cat's milk contains almost three times as much protein as cow's milk. Orphan kittens fed only cow's milk will not survive because they are not getting sufficient protein in their diet. If you find yourself in the position of surrogate cat-mom, make sure you feed the little ones a nutritionally adequate diet. Consult your veterinarian or feed the kittens one of the commercial products designed for this purpose. Cow's milk can occasionally be a problem for cats that do enjoy it. Some adult cats cannot effectively digest cow's milk (lactose intolerance), which can result in diarrhea. The diarrhea should stop after you remove milk from your cat's diet. But if the diarrhea persists, lactose intolerance may not be the problem, and you should consult your veterinarian.

source: http://www.cah.com/dr_library/catfood.html