Sweetness is detected by a specific receptor protein (‘taste bud’) in the tongue. Cats are known to be insensitive to sweet tastes. Researchers analyzed the genes encoding the taste buds in twelve different carnivorous species, including cats. They found that those species such as cats, whose diet is exclusively meat-based (obligate carnivores), had lost the gene encoding the taste bud for sweetness. Other affected species included dolphins, sea lions, seals, otters, and hyenas. It appears that the ability to taste sweets has been lost in most carnivorous species since a meat-based diet does not consist of sugars or carbs, there was no need to be able to detect (or enjoy!) these substances.
This supports the fact that cats should not eat carbohydrates except in very small pre-digested quantities, if at all. The main reason cats will eat carbohydrate loaded dry food is because the pet food companies spray it with an animal digest to diguise the flavorless food with a meaty taste.
Major Taste Loss in Carnivorous Mammals March 2012