July 26, 2005

Why cats will never live the sweet life

WASHINGTON -- Cats may like ice cream, but it is not the sugary taste that appeals to them because they are genetically unable to taste sweet flavors, researchers reported on Monday.

Domestic cats and big cats alike have a slightly different version of the sweet receptor gene than other mammals, the British and U.S. scientists found.

Any cat owner knows that cats have individual preferences, but cats will turn their noses up at sugary treats that do not contain some other ingredient such as butter or gelatin.

"One possible explanation for this behavior is that felines are unable to detect sweet-tasting compounds like sugars and high intensity sweeteners because their sweet taste receptor is defective," said Xia Li, a molecular geneticist at the Monell Chemical Senses Center, a nonprofit research institute in Philadelphia, who helped lead the study.

"An obvious place to look, therefore, is at the genes coding for the sweet-taste receptor."

So they did. Mammals taste sweet flavors via a receptor, a kind of molecular doorway, called T1R on their taste bud cells. It has two subunits, known as T1R2 and T1R3. Each is coded for by a separate gene.

Writing in the online journal Public Library of Science Genetics, Li and colleagues said they found a change in the gene encoding the T1R2 protein in domestic cats, tigers and cheetahs.

"Other than this sweet blindness, the cat's sense of taste is normal," the researchers wrote in their report.

"The non-functional sweet receptor provides a molecular explanation for why cats have no avidity for sweets," said Joseph Brand, a biophysicist at Cornell who worked on the study.

"Looking beyond this elegant explanation, one can contemplate the importance that this molecular change had on the evolution of the cat's carnivorous behavior," Brand added in a statement.

"What we still don't know is -- which came first: carnivorous behavior or the loss of the T1R2 protein? With regard to the gene, is this a case of use it or lose it?"

Many animals in the carnivore family like sweet things, including bears, dogs, raccoons and others.

"I say jokingly, no wonder cats are cranky -- not only do they have to hunt for their food, but they also can't enjoy a sweet dessert," Brand said.