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Finickiness, Explained: Cats Can't Taste Sugar, But They Can Taste Bitterness

This article is more than 8 years old.

Every kind of animal experiences flavor in its own way. Thanks to DNA decoding technology, we know that pandas – which, at some point in the past were meat-eaters – lost the ability to taste umami, or savoriness, at some point after switching to a bamboo-only diet. We know that some whales and dolphins are able to taste only salt. On the surface, these findings suggest one obvious explanation: when a species has no need to detect a particular taste, the genes become inactive. Use it or lose it, in other words. (In this regard, humans are lucky: we’re omnivores descended from scavengers, so our tastes remain diverse.)

But a new animal taste study – on cats – throws this theory into doubt. Because cats eat only meat, we’d expect them to have limited tastes; indeed, recent studies have shown that they cannot taste sweetness. But the paper by scientists at the Monell Chemical Senses Center found that despite having no plants – the principal source of bitter compounds in nature – in their diet, cats can still taste bitterness.

The found that cat DNA contains the code for at least seven functioning bitter receptors, the proteins on the tongue that detect the chemical signatures in food. That’s not a lot – humans, for instance, have two dozen working bitter genes – but it’s enough to detect a diverse range of compounds and concentrations.

Why would cats need to detect bitterness? It’s complicated.

Most scientists believe that the bitter taste evolved as a kind of poison warning – a visceral, aversive sensation demanding “spit that out!” Many of the hundreds of known bitter compounds tend to be mildly-to-highly toxic. But bitterness is also something of a mystery. There are far more bitter receptor genes than for any other taste. A lot of bitter compounds are healthy in small or moderate amounts. And among humans, there is a huge range of sensitivity to them. (This is why some people really hate broccoli while others like it.) Clearly there are certain biological benefits to not spitting bitter foods out, meaning the poison warning theory doesn't always make sense. The cat study ads another wrinkle.

The Monell scientists have several ideas about cats’ unexpected taste for bitterness. Maybe it helped their ancestors, and helps them, sense toxic compounds that their plant-eating prey have already consumed. Or, it may be about the prey’s bodily fluids: “domestic cats,” the paper notes, “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.” Mmm.

Their third theory is more tantalizing. Bitter taste receptors are found not just on the tongue but in the gut, the nasal passages, and many other places in the body. Their purposes are still mostly obscure to scientists, but they may play a roles in digestion and metabolism. So it might be useful for an animal to retain some bitter genes for these hidden purposes, even if it never eats anything bitter.

But on a more practical level, for pet owners, the taste for bitterness may help explain why cats are such picky eaters.

 

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