Why Cats Can’t Taste Sugar

Cats and many other carnivore species have lost their sweet taste receptors

It is already known that both domestic and wild cats are unable to taste sweet compounds due to defects in a gene that controls the structure of their sweet taste receptor. Now in a study published online in Proceedings of the National Academy of Sciences, scientists at the Monell Chemical Senses Centre have examined 12 related mammalian species with varying dietary habits, and once again found extensive taste loss particularly widespread in meat-eating species.

According to a press release, ‘senior author Gary Beauchamp, a behavioural biologist, comments, “Sweet taste was thought to be nearly a universal trait in animals. That evolution has independently led to its loss in so many different species was quite unexpected”.’

The integrity of the sweet taste receptor gene was closely related to the animals’ diets. The sea lion, fur seal, Pacific harbor seal, Asian otter, spotted hyena, fossa and banded lingsang, species that are exclusive meat eaters, all had defective sweet receptor genes. In contrast, intact sweet receptor genes were found in the aardwolf, Canadian otter, spectacled bear, raccoon and red wolf. These species include both exclusive meat-eaters and those that also eat other foods in addition to meat.

Further examination revealed that the defective portion of the sweet receptor gene varies among the seven species with non-intact receptors. Together, the findings suggest that diet-related taste loss has happened repeatedly and independently throughout evolution, demonstrating the importance of a dietary niche in the structure and function of an animal’s sensory system. The researchers next examined sweet and umami taste receptor genes in two mammals that have ‘returned’ to the sea, the sea lion and bottlenose dolphin. These animals were selected because they swallow their food whole, suggesting that taste may not play an important role in their dietary selection. As predicted, taste loss was extensive in these animals. Sweet and umami receptor genes were non-functional in both, and the dolphin also had non-functional bitter taste receptor genes. “Our findings provide further evidence that what animals like to eat—and this includes humans—is dependent to a significant degree on their basic taste receptor biology,” says Beauchamp.

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