Cats Cannot Taste Sweetness

Put a slice of cake in front of a dog and it may well vanish. Put the same slice in front of a cat and you are likely to get a sniff, a moment of polite interest and then a walk away. For a long time this was simply filed under cats being cats. In 2005, scientists found a much more precise explanation. Cats are not being fussy about sugar. They are missing the equipment needed to taste it in the first place.

The work came from the Monell Chemical Senses Center in Philadelphia, in collaboration with the Waltham Centre for Pet Nutrition in the United Kingdom, and was published in the journal PLOS Genetics. As the paper explains, the sweet taste receptor in mammals is formed by two proteins working together as a pair, called T1R2 and T1R3. Both parts are needed. Without one of them, the receptor that detects sweetness cannot be built.

In cats, the gene for T1R2 is broken. The researchers found a deletion of 247 base pairs, a missing stretch of genetic code, along with stop signals that cut the instructions short. As ScienceDaily reported, this prevents the T1R2 protein from being produced at all, so it cannot join T1R3 to form a working sweet receptor. The paper describes the cat gene as an unexpressed pseudogene: a gene that is still present but no longer does its job.

That fits what cats actually do. The researchers note that cats are indifferent to things that taste sweet to humans, including sugars and high-intensity sweeteners. The fault is not limited to pet cats either. The team also examined tigers and cheetahs and found a similar deletion and stop signals in the same gene. According to ScienceDaily, the researchers suggested this defect is common to species throughout the cat family.

Why would such an important sense disappear? The researchers point to diet. Cats are strict meat-eaters, and the paper concludes that this molecular change was very likely an important event in the evolution of the cat’s carnivorous behaviour. An animal that eats meat has little need to detect the sweetness of ripe fruit, so losing the ability to taste it may have cost cats very little over their long evolutionary history.

So if your cat is standing on the kitchen table licking a bowl beside the cake, something other than sweetness has caught its interest. Whatever draws it to that bowl, it is not the sugar, because a cat’s tongue simply has no way of telling it is there. It is one of those small facts that changes how you see an ordinary moment at home. The cake is safe from your cat’s sweet tooth, because your cat does not have one. The cream, on the other hand, may be a different story.