Here are some random facts about cat nutrition, in no particular order:
Cats require about twice as much protein per unit of body weight as dogs do, and more than 3 times as much as rats
As is the case for many of the cats peculiarities, the liver is responsible for the higher protein requirements. The cat liver can't decrease protein use when protein is scarce.
Most carnivores require 8 amino acids as essential, cats have 10.
Deficiency of the amino acid Taurine cause problems with cat's eyesight and heart failure.
High intakes of sugar can lead to glucose in the urine, extremely uncommon in most animals.
Providing glucose only diets to cats can kill them. They die from dehydration trying to rid themselves of the sugar.
Cats are unable to make enough Vitamin D even if they are shaved and subjected to intense light. (don't try this at home, they also get sunburn very easily!)