We often see amused videos of dogs eating sweets online, but rarely do we see cats enjoying desserts. Are these proud felines simply too disdainful of human treats? Actually, there's a profound scientific explanation behind it. Let's take a look at why cats don't eat sweets. 
Most mammals have taste receptors on their tongues—proteins on the surface of cells that activate internal cell processes when food enters the mouth, sending a signal to the brain. Humans can taste five (possibly six): sour, bitter, salty, umami, and sweet. The sweet taste receptors are typically composed of two pairs of proteins produced by two different genes—Taslr2 and Taslr3.
Whether this is due to dietary choices or not, all felines—lions, tigers, and British Shorthairs—lack the 247 base pairs that make up the Taslr2 gene. The result is an inability to produce the correct protein; because they can't form the designated gene (they only form pseudogenes), cats can't taste sweetness. "They can't taste sweetness like we do," says Joe Brand, associate director of the Monell Chemical Sensing Center in Philadelphia. "They're lucky. Cats have really bad teeth."
For us humans, the energy source is sugar. That's why we perceive sugar as "sweet." When we're tired, we crave sweet things because our bodies need energy. For carnivorous cats, however, their energy comes from protein. Therefore, cats are very sensitive to the sweetness of the amino acids in protein. The sweetness of crab meat also comes from the sweetness of amino acids. Because they can't perceive the sweetness of sugar, they can't digest it well. Although cats like to eat whipped cream, it's not because they're reacting to the sugar, but because they like the fat in it.
To date, felines are the only mammals lacking the gene for sweetness; even their close carnivorous relatives, hyenas and mongooses, possess this gene. Cats may also lack other components for enjoying or digesting carbohydrates, such as glucoskinase in the liver—a key enzyme that controls carbohydrate metabolism and prevents excess glucose. Furthermore, most mainstream pet food manufacturers use corn or other grains in their products. "This may be why more and more cats are getting diabetes," Brand said. "Current cat food contains about 20% carbohydrates. Cats are not used to it and cannot process it on their own."
After reading the above explanation, you probably understand why cats don't like sweets. So next time, don't try to feed your cat sweets; after all, they are carnivores. Meat is the only true food, and it's their favorite.
