Cats are obligate carnivores. This means they should only eat meat. And it should be raw. Download and read this article carefully: The Carnivore Connection to Nutrition in Cats. It may seem very scientific at first, but the conclusion is: cats are what they eat and they are strict carnivores.

Then there is Dr. Pottengers Cat Study. This is the longest study on cat nutrition and it is the only one of its kind to span multiple generations. I won’t give too many details, you can find those on your own, but the conclusion was that cats fed anything other than raw meat had the following health problems:

  • By the end of the first generation the cats started to develop degenerative diseases and became quite lazy.
  • By the end of the second generation, the cats had developed degenerative diseases by mid-life and started losing their coordination.
  • By the end of the third generation the cats had developed degenerative diseases very early in life and some were born blind and weak and had a much shorter life span. Many of the third generation cats couldn’t even produce offspring. There was an abundance of parasites and vermin while skin diseases and allergies increased from an incidence of five percent in normal cats to over 90 percent in the third generation of deficient cats. Kittens of the third generation did not survive six months. Bones became soft and pliable and the cats suffered from adverse personality changes. Males became docile while females became more aggressive.
  • The cats suffered from most of the degenerative diseases encountered in human medicine and died out totally by the fourth generation.

At the time of Pottenger’s Study the amino acid taurine had been discovered but had not yet been identified as an essential amino acid for cats. Today many cats thrive on a cooked meat diet where taurine has been added after cooking. The deficient diets lacked sufficient taurine to allow the cats to properly form protein structures and resulted in the health effects observed. Pottenger himself concluded that there was likely an “as yet unknown” protein factor (taurine) that may have been heat sensitive.

(straight from Wikipedia)

What is important to take from this study, is that each cat will be different. For example, a cat whose family has been fed a more species appropriate diet will have less health issues in its own life time. A cat whose ancestors have been fed a less species appropriate diet will have more health issues.