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If your house is anything like mine, holiday leftovers are taking over the refrigerator. Why not share the wealth and give your cats a treat?

Good luck with that! Scientists are starting to get to the bottom of just why cats can be so finicky.

We’ve talked before about how cats don’t have functional genes that allow them to taste sweet flavors (put away the pumpkin and pecan pies). On the other hand, recent research published in the journal PLoS One has shown that they have “at least seven functional bitter taste receptors.” This is a little odd since traditionally we have thought that the need to detect bitter substances was most important to plant eaters. As the authors of this new paper put it:

Compounds that taste bitter to humans … are widely rejected throughout the animal kingdom. It is thought that rejection is based on a mutual interaction between plants that do not “want” to be eaten and animals that do not “want” to be poisoned.

So why would an obligate carnivore like the domestic cat still have so many functional genes that allow them to taste (and presumably avoid) bitter substances?

First, it could be that even obligate carnivores such as cats are actually exposed to plant material through consumption of prey viscera that contains plant material consumed by the prey. There are two arguments against this having an important role. First, plants eaten by prey may not be bitter and highly toxic since the prey species consumed them themselves. However, some species have evolved detoxification mechanisms enabling them to consume potentially toxic plants (e.g., the koala [Phascolarctos cinereus] feeding on the foliage of eucalyptus species, which are typically rather poisonous to most animal species) [30]. Second, the frequency that carnivores actually consume plant material in prey viscera is unclear and it has been reported, at least for wolves, that this plant-material is avoided [31].

Another possible reason for maintenance of bitter receptor number and function in cats and perhaps other carnivores is that there are also bitter compounds in many non-plant prey items in the carnivore diets (but see reference [5]). For example, domestic cats are known to feed on animal products that are also potentially bitter and toxic such as bile acids, venom and skin secretions from arthropods, reptiles and amphibians [32]. Thus our observations that bitter receptors in cats and most likely other land-dwelling Carnivora are functional could be due to selection to insure that consumption of these toxic substances is minimized.

A third reason why the number of bitter taste receptors may not be strongly influenced by the amount of dietary plant material relates to the possible non-oral functions of these receptors. Bitter receptors are found in cell types other than taste on the tongue. Neither the natural ligands [a molecule that binds to another] nor the functions of these receptors are fully known, but we suggest they may be important in maintaining bitter receptor functionality in species that might not otherwise “need” them to avoid plant-based or animal-based toxins. For instance, respiratory-expressed bitter receptors are important for innate defense against bacterial infections [3335].

Whatever the reason, it’s important for us to keep in mind that cats simply can’t appreciate sweet things and are genetically predisposed to avoid bitter ones, which probably explains why they are really only interested in the leftover meats.

Dr. Jennifer Coates


Functional Analyses of Bitter Taste Receptors in Domestic Cats (Felis catus). Lei W, Ravoninjohary A, Li X, Margolskee RF, Reed DR, Beauchamp GK, Jiang P. PLoS One. 2015 Oct 21;10(10):e0139670. doi: 10.1371/journal.pone.0139670. eCollection 2015.

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