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What is cat food made of?

In general, cat food consists of water, proteins, fats, carbohydrates, vitamins, and minerals. But how close your cat's diet comes to that of its feral cousins depends on what formula the cat food manufacturer uses.

Proteins are the basic building blocks for cells, tissues, and organs. They can be either animal-based or plant-based, and either type may show up in cat food. Soy, vegetables, and cereals are examples of plant-based proteins. Chicken, lamb, turkey, and fish are examples of animal-based proteins. In addition, cat food often contains byproducts of animals or plants, the parts that people don't normally eat.

Cats are meat eaters. They require two to three times the protein that omnivores, such as dogs or humans, do.

As strict carnivores, cats rely mainly on nutrients found in animals -- high protein, moderate fat, and minimal carbohydrates -- to meet their nutritional needs. Cats' bodies are adapted for metabolizing animal protein and fats. And animal-based proteins also contain complete amino acids -- such as taurine, arginine, cysteine, and methionine. These are essential for cats, whose bodies don't make them in adequate amounts.

Although carbohydrates provide energy, cats use them less efficiently as an energy source. Their bodies need a steady release of glucose from protein.

Fat, the most concentrated form of energy, helps cats absorb fat-soluble vitamins and provide essential fatty acids that cats can't make well. These include omega-6 fatty acids and omega-3 fatty acids.

For good nutrition, cats also need vitamins, such as A, B, D, E, and K, as well as minerals including calcium and phosphorus.
Which is better, dry cat food or canned?

Controversy surrounds cat nutrition, just as it does human nutrition. And few topics garner more attention than the canned vs. dry food debate.

Jennifer Larsen, DVM, PhD, is a nutritional consultant and assistant professor of clinical nutrition at the Veterinary Medical Teaching Hospital at the University of California, Davis. She says that a high-quality brand of cat food -- either wet or dry -- can be nutritionally complete. However, Larsen also tells WebMD, "Some cats benefit from the higher moisture content of wet food, which makes their urine more dilute. But most cats do fine on dry. It's an issue of personal preference."

Other veterinarians draw a line in the sand on this subject. Among them is Lisa A. Pierson, DVM, a practicing veterinarian in Lomita, Calif.

Pierson has three concerns about dry food -- moisture, carbohydrates, and type of protein. "By and large, the canned food is going to have more meat, more protein from animals," Pierson says. "In the dry food, a lot is often coming from plants."