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Tuna are big, fast-swimming ocean fish. They're hardly the natural prey of cats, whose ancestors evolved in the desert. Yet a study of taste receptors in cats shows that they're predisposed to LOVE tuna.

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[ ♪ INTRO ♪] Picture this: Your favorite feline splashing around in the ocean, diving under the waves, taking down a southern bluefin tuna the size of a bear… But Wait, no!

That’s all wrong. Mr.

Whiskers fits neatly into a handbag and prefers sunbeams over surf. There is exactly no chance he’s taking on a tuna. So why does he lose his mind when you pop open a can of Starkist?

It doesn’t make a whole lot of sense, because cats evolved in the desert, where there is literally no tuna. Or any other kind of fish. Their ancestors were wild cats native to north Africa and southwest Asia, and they've likely been living alongside us since the early Neolithic period.

Fast forward a few thousand years to the invention of Fancy Feast, and the arrangement is working out pretty well. But there’s no denying that most cats would choose a stinky can of tuna over the dozens of available Fancy Feast flavors. Cats – and humans, too – enjoy certain foods because of the umami.

Umami is the word that describes savory, meaty flavors. In both cats and humans, the ability to taste umami has to do with two proteins called Tas1r1 and Tas1r3. In humans, these two molecules form a receptor that detects the amino acids glutamic acid and aspartic acid, which make your brain say “umami.” Amino acids are the components that make up protein, so it makes sense for them to taste good.

That’s valuable energy right there! In fact, glutamic acid is the stuff in food additive MSG – it’s basically pure umami flavor. Nucleic acids also play a role, acting as flavor enhancers.

When you hear the term “nucleic acid,” you might think of DNA and RNA. Those are the most familiar types of nucleic acids, but there are also a variety of nucleic acids present in all kinds of biological tissue – including food. These compounds help give food its flavor.

But in cats, the ability to taste umami works sort of opposite to the way it works in humans. They’re tasting an almost totally different umami to what we taste. In a 2023 study, researchers used computer modeling of protein structure as well as cell line studies of cat taste receptors to help suss this out.

And before you accuse them of taking their research too seriously, they also did cat taste tests. This helped them figure out what molecules in food were the primary drivers of whether a cat thinks something tastes good. In cats, the Tas1 receptor pair is not activated by just amino acids.

Instead, it’s activated by certain nucleic acids and enhanced by amino acids. A nucleic acid called inosine monophosphate, or IMP, is enhanced by a number of different amino acids, including one called histidine. And for cats, the IMP and histidine combo is a powerful flavor combination. really takes them to flavor town.

Tuna just happens to contain a lot of IMP and a lot of histidine. In fact, it has more IMP than any other nucleotide, and more histidine than any other free amino acid. So, that does explain why Mr.

Whiskers begs for your tuna salad sandwich even though he’s not ever going to single-handedly land a bluefin. Other types of fish also contain these components, but not as much of them. Even rat meat, a more likely prey item for cats, is pretty low in histidine.

And meats like chicken, beef, and pork don’t seem to have any free histidine at all. The good news is, cats also like other combinations of amino acids and nucleic acids. So they’re not going to come for you in your sleep if you put something else in their bowl.

I mean, Probably. So why would cats evolve to prefer something that lives thousands of miles from their homeland in an environment they could never physically enter? Well that’s… not super clear.

A researcher who was not involved with the study speculated that cats who hung around fishing ports eating scraps long, long ago might have had an advantage over the ones who still had to catch mice like a bunch of suckers. And there’s evidence that domesticated cats were eating fish thousands of years ago, so it’s not like this is a super recent development. So your kitty’s food preferences basically have more to do with the interactions between amino acids and nucleic acids than with what their wild ancestors ate, or even what’s good for them.

Which is why we should note that not only is tuna not natural prey for cats, it’s also not especially healthy. Neither raw nor canned tuna are nutritionally complete, so tuna should be a treat, not a main meal. And even though you might never get to see Mr.

Whiskers pull humongous fish out of the ocean, maybe it’s enough to know that he totally wants to. And it won’t hurt to give him a spoonful of the stuff every now and then. That way you can both pretend.

Now If you enjoyed this fun, lively story about the science of cats and thought “Man, my kids slash students slash nieces and nephews would love this if it was just written on a second grade level with some educational standards thrown in,” ok, And you might say “Stefan, that’s very specific” but also I have good news for you. Because we have a whole channel just for kids, and we have an episode where Squeaks the robot rat learns about why cats have whiskers, Which you can find a link to in the description. SciShow Kids is written with early-grade Next Generation Science Standards in mind to help kids grasp age-appropriate ideas.

And it’s also just a ton of fun. So send the young curious mind in your life to, and thanks for joining us today. [ ♪ OUTRO ♪ ]