Sweetness is detected by a specific receptor protein (what we commonly refer to as a ‘taste bud’) in the tongue. Cats are known to be insensitive to sweet tastes, but the specific reason was not known until recently.
Researchers analyzed the genes encoding the taste buds in twelve different carnivorous species, including cats (“Major taste loss in carnivorous mammals,” in Proceedings of the National Academy of Sciences, US, 2012 ). They found that those species such as cats — whose diet is exclusively meat-based — had lost the gene encoding the taste bud for sweetness.
Other affected species included dolphins, sea lions, seals, otters and hyenas. An animal with a diet devoid of vegetables may have little need to detect sugars, explains Gary Beauchamp, director of the Monell Chemical Senses Center in Philadelphia, PA, and the lead author of the study.