Cats lack the proper genetic coding that allows other mammals, including humans and other animals such as hyenas, to experience sweet tastes, a trait that may be unique among mammals. In addition to lacking the ability to taste sweets, cats have only 470 taste buds, whereas humans have upwards of 9,000. However, this doesn't mean that cats don't experience flavor; on the contrary, taste buds are a small part in the complex anatomical system, which includes their acute sense of smell, that allows cats to experience vivid taste.
Because cats have evolved as carnivores, they theoretically don't need to taste sweets, which are found in non-meat foods. While there may be some cats with a sweet tooth, scientists have yet to study such specimens, and the conventional wisdom is that cats do not have the ability to experience sweet tastes. The same mechanisms (or lack thereof) that make it impossible for cats to experience sweet flavors also make it hard for these animals to digest carbohydrates, information that seems lost on major pet food manufacturers. According to Joe Brand, a biochemist with the Monell Chemical Senses Center in Philadelphia, this may be why diabetes has become a problem in so many domestic cats.