Why Cats Like Fish

Cats are carnivores. In fact, they are obligate carnivores, which means that their digestive system has evolved to deal with meat and basically only meat. They can’t properly digest fruits or vegetables, for example. If you have a cat, you probably know all this.

But here is a puzzle. Cats love fish. Pretty much all fish, but especially tuna. How can that be if they are obligate carnivores?

A new study about the taste perception of cats can help us answer this question, which every cat owner has, no doubt, asked themselves at one point. And the results of this study are important in their own right as they help us understand the difference between how cats and humans perceive the world.

Our tongue is only capable of discerning five basic tastes: sweet, sour, bitter, salty, and umami.

And the same is true of other mammals. This doesn’t mean that these are the only five flavors. It might be tempting to think that you taste food with your tongue—just as we perceive sound with our ears and we perceive colors with our eyes. But this is completely wrong.

Everything besides the five basic tastes of sweet, sour, bitter, salty, and umami comes from smell—from what researchers call “retronasal olfaction” (smell activated not by sniffing but by the air pushed upwards from the back of the palate). If we block smell, strawberries, and mango will taste the same: sweet. Flavor perception is multimodal: smelling and tasting (and heat perception and the trigeminal nerve) all contribute to what our food tastes like.

But let’s focus on the five basic senses here. Until 1908, researchers only acknowledged four of these—umami is a late addition. And that may not be surprising: Strawberry is sweet, lemon is sour, arugula is bitter, and capers are salty. We are very familiar with these tastes. Even small children are.

But what is umami?

Umami is a Japanese term that could be roughly translated as “savory and pleasant.” It was introduced by the Japanese chemist Kikunae Ikeda, but we now know that while some receptors on our tongue are sensitive to sweet, sour, bitter, and salty tastes, others are specifically sensitive to umami. They are activated when we eat food like soy sauce, various fermented products, meat broth, the flavor enhancer MSG, mushrooms, tomatoes—and also fish.

While the human tongue can discern umami, it is not a taste that plays a huge role in our appetitive behavior. We very rarely seek out umami food explicitly. But we often do go after sweet (or sometimes salty) food. In fact, we sometimes go out of our way to do so. This difference is probably the reason why the umami taste has not even been talked about until a little over a hundred years ago.

But cats are different.

Their umami receptors are sensitive to a much wider range of glutamates and nucleotides than human umami receptors. Given that the main component of their diet is meat, an umami-rich food, this is to be expected. And as a result, the taste of umami plays a much more significant role in cat’s appetitive behavior: They actively seek out food that tastes umami—much like we actively seek out sweet stuff.

This explains why cats love fish, although their digestive system has evolved for meat consumption. Humans have evolved to seek out sweet food—a very adaptive behavior in environments where fruits are rife. But as a result, it’s difficult for us to resist a double fudge chocolate sundae—although, at this point, a double fudge chocolate sundae is very unlikely to enhance your evolutionary profile.

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And the same is true of cats and fish. They have evolved to discern the main taste component of meat, but given that fish has the same taste component—umami—it is very difficult for them to resist fish. To put it simply, fish is a double fudge chocolate sundae for cats.

And, just to drive home the point, one of the most umami-rich kinds of fish is exactly the all-time cat favorite—tuna.