SWEETNESS AND LIGHT: Cats, like Schrödinger pictured here, lack the gene that permits mammals to taste sweetness.
Image: LEA REID
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Sugar and spice and everything nice hold no interest for a cat. Our feline friends are only interested in one thing: meat (except for saving up the energy to catch it by napping, or a round of restorative petting) This is not just because inside every domestic tabby lurks a killer just waiting to catch a bird or torture a mouse, it is also because cats lack the ability to taste sweetness, unlike every other mammal examined to date.
The tongues of most mammals hold taste receptors—proteins on the cellular surface that bind to an incoming substance, activating the cell's internal workings that lead to a signal being sent to the brain. Humans enjoy five kinds of taste buds (possibly six): sour, bitter, salty, umami (or meatiness) and sweet (as well as possibly fat). The sweet receptor is actually made up of two coupled proteins generated by two separate genes: known as Tas1r2 and Tas1r3.
When working properly, the two genes form the coupled protein and when something sweet enters the mouth the news is rushed to the brain, primarily because sweetness is a sign of rich carbohydrates—an important food source for plant-eaters and the nondiscriminating, like humans. But cats are from the noble lineage Carnivora and, unlike some of its lesser members, such as omnivorous bears or, even more appalling, herbivorous pandas, they exclusively eat meat.
Whether as a result of this dietary choice or the cause of it, all cats—lions, tigers and British longhairs, oh my—lack 247 base pairs of the amino acids that make up the DNA of the Tas1r2 gene. As a result, it does not code for the proper protein, it does not merit the name gene (only pseudogene), and it does not permit cats to taste sweets. "They don't taste sweet the way we do," says Joe Brand, biochemist and associate director at the Monell Chemical Senses Center in Philadelphia. "They're lucky. Cats really have bad teeth as it is."
Brand and his colleague Xia Li first discovered the pseudogene after decades of anecdotal evidencesuch as cats showing no preference between sweetened and regular water, unlike other animals—testifying to their indifference to the sweet stuff. Of course, there are also plenty of anecdotal accounts pointing in the other direction: cats that eat ice cream, relish cotton candy, chase marshmallows. "Maybe some cats can use their [Tas1r3 receptor] to taste high concentrations of sugar," Brand says. "It's a very rare thing but we don't know yet."
Scientists do know, however, that cats can taste things we cannot, such as adenosine triphosphate (ATP), the compound that supplies the energy in every living cell. "There isn't a lot hanging around in meat, but it's a signal for meat," Brand says. And plenty of other animals have a different array of receptors, Li says, from chickens that also lack the sweet gene to catfish that can detect amino acids in water at nanomolar concentrations. "Their receptor is more sensitive than the background concentration," Brand notes. "The catfish that detects the rotting food first is the one that survives."
So far, cats are alone among mammals in lacking the sweet gene; even close relatives among the meat-eaters like hyenas and mongooses have it. And cats may lack other components of the ability to enjoy (and digest) sugars, such as glucokinase in their livers—a key enzyme that controls the metabolism of carbohydrates and prevents glucose from flooding the animal. Despite this, most major pet food manufacturers use corn or other grains in their meals. "This may be why cats are getting diabetes," Brand offers. "Cat food today has around 20 percent carbohydrates. The cats are not used to that, they can't handle it." What these fearsome predators of suburbia cannot taste may be hurting them. But it also means that most cat lovers don't have to worry about Simon snatching their unattended dessert.
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28 Comments
Add CommentIf cats don't like sweets, why is my cat crazy for fortune cookies, baklawa and ice cream? He attacks it to eat it like he can't get enough!
Reply | Report Abuse | Link to thisWe have 4 cats, and one or all of them kept breaking into our sugar bowls with covers and eating the sugar, and they drank a 2 cup measure cup of hummingbird sugar water which was cooling down before being put out. We have to put our table sugar into a sealed container that won't spill, and I have to chill the bird water outside. They may not taste sugar, but they like the taste that it does make very much.
Reply | Report Abuse | Link to thisThe Thai diet specifies five flavours to be part of every dish: sweet, salty, sour, bitter and, at least for humans, the one you left out: SPICY!
Reply | Report Abuse | Link to thisMy cat is a rescued stray who was born during date season in Saudi Arabia, where I worked. She was an indoor cat for her first 6 years in Saudi, and then travelled back to Australia with me when I retired. She is now an outdoor cat aged nearly 10 and since living here I've discovered her delight for dates - she beats me up to get at them when I open a packet. I am assuming there is a deep-seated memory of her scavenging when she was a tiny kitten and possibly finding nothing to eat but fallen fruit. She shows no interest at all in anything else sweet.
Reply | Report Abuse | Link to thisMy Egyptian Mau, Moe, is rendered "puffy tailed" and practically feral in pursuit of pop tarts and Linden's sugar cookies (of which he gets a tiny taste every so often). Maybe he can't taste the sugar, but there's little else in those treats. I think the sweeping conclusion in the article is premature. My cat thinks so, too.
Reply | Report Abuse | Link to thisI tend to agree. My cat, Paris, goes after sweets like they are going out of style. Conversely, she often snubs tidbits of human tablefood... like rotisserie chicken and tuna. She likes ice cream, scones, licking the sugar off the top of pastries, and don't even think about not oferring her the crumbs off your crumbcake! Gene mutation, morphing? Anyone?
Reply | Report Abuse | Link to thisApart from altered taste perception, I suspect cats can detect elevated CO2. My cat was extremely sensitive to carbonated drinks, a mere whiff of fizz was clearly over powering. I wonder if the cat's nose can smell the CO2 in the breath of e.g. rodents hiding in the undergrowth. As for sweet perception, perhaps there is another gene that gives them some sort of sweet perception, before reading this article I assumed from my cats food preference he could taste sweet foods.
Reply | Report Abuse | Link to thisI once had a cat who loved cantaloupe. My current three cats take turns going after green beans and asparagus, although perhaps it's the 'tail like' proportions of those veggies that attract them. One of ours now, however, is the 'cracker kitty', who will go into boxes of Wheat Thins, Triscuits etc, and just today, stole the caramel covered paper wrapper from a caramel apple....mostly sugar.
Reply | Report Abuse | Link to thisIn response to jillih, I had a cat who loved cantaloupe and corn (canned and on the cob - both are sweet tasting).
Reply | Report Abuse | Link to thisgc
I have a 9 month old Manx kitten who loves everything sweet. He will attempt to force open your mouth if you have candy. He fights you for anything sweet. The day after Thanksgiving we found that he had uncovered a pecan pie, moved the pecan out and ate the sugary goop out of the center!
Reply | Report Abuse | Link to thisWell, if cats can't taste sweet like us, then whatever it tastes like to them must taste really good. My kitty LOVES anything that is sweet. In fact, she prefers that over her kitty treats. I have caught her eating a jelly donut, both licking the sugar off the donut and then eating the jelly and donut parts. I've caught her drinking soda out of my roomate's cup. And her new thing is eating canned whipped cream. When she hears me using the can, she comes running and swats and meows at me until I give her some.
Reply | Report Abuse | Link to thisSo, perhaps more research needs to be done here as I don't think science has figured this one out yet.
Wow, it's like you people didn't even bother to read the article. He says very clearly that there is anecdotal evidence of cats liking high concentrations of sugar, postulating that their tas1r3 might fire with very sugary or sweet things... then you all go on to post your anecdotes as if the article didn't say this very thing. People's lack of attention totally amazes me.
Reply | Report Abuse | Link to thisI'm not so sure about cats not being able to taste sweets. One of our cat's loves Mexican sweet bread. She licks the sugar off the top.
Reply | Report Abuse | Link to thisYeah, I think in many cats this may be accurate, but I've had 2 cats (out of a total of 8, not counting the 30 or so that were outside cats of the people I lived beside. Who show(ed) GREAT interest when I ate anything caramel, or starburst fruit chews, or a handful of other candies/cookies. Fortunately, I'm not often into sweets, and usually when I am it's Heath bars and they seem ambivalent about those.but Tiernan (current feline sweets nut) goes nuts when I have starburst, certain cookies, skittles or milkduds (of course I make certain that the chocolate is all washed off in warm water 1st. now caramel is cooked sugar so..... makes me skeptical some species/hybrids have not some sense of "sweet".
Reply | Report Abuse | Link to thisya know they also say at the closing of the article: "But it also means that most cat lovers don't have to worry about Simon snatching their unattended dessert."
Reply | Report Abuse | Link to thisI disagree. One of our cats (Paddy) loves cake frosting. She has been known to lick it off a plate full of cupcakes. She will eat almost anything though, even dog food. The only thing she won't eat is McDonald's sausage. She smells it then gives me a look like, "Are you crazy?" Do a study on that one SA.
Reply | Report Abuse | Link to thisMy 19 year old cat Stevie seems to love sugar; whenever we have waffles he begs for some, so we give him a taste, and he only eats the parts with syrup on. Also, we cannot leave Easter baskets unattended because if we do, we will find that the chocolate has mysteriously been licked.
Reply | Report Abuse | Link to thisI realize I'm late to the party, but I noticed a minor error in the article.
Reply | Report Abuse | Link to thisA sentence in the 4th paragraph says, "lack 247 of the base pairs of amino acids that make up the DNA...," but DNA is made of nucleotides, not amino acids. If 247 nucleotides were deleted from the DNA, instead, the result would a loss of 82.3 amino acids from the protein it's supposed to encode, or, realistically, 82 lost amino acids and a missense mutation in the rest of the gene (after the mutation) which would in all likelihood end up producing a major POS protein that has, say, none of its original capacity to recognize certain sugars bound to its surface, for example...
We have 2 cats. One will eat dry cat food and NOTHING else.
Reply | Report Abuse | Link to thisThe other cat eats ANYTHING and EVERYTHING,
but he especially LOVES SWEETS.
If science is the search for truth,
I have to say whatever "science" says ALL cats can't
taste "sweet" is faulty.
From the other comments I've read here, this is not
just anecdotal.
My cat hates wet food! If he even thinks you might have something sweet he's standing right over your shoulder until you let him smell it. The only he tries to taste is ice cream and whipped cream. He won't touch meat unless it's tuna. I think these "Scientists" need to do a little more research
Reply | Report Abuse | Link to thisSome cats LOVE sweets. I had a cat that would just about take me down for a Little Debbie cake. All it took was for her to hear the rattle of the paper and she'd come running.
Reply | Report Abuse | Link to thisi highly doubt can't cannot taste sweets. My balinese cat eats everything sweet in the world. She sleeps in the bathrrom on the vanity all the time and when i open up her cat food she doesn't come running...I have to go pick her up and bring her to eat. she is 10 yrs old. But if i open a piece of candy, or chocolate popcicle, or a Nutrigrain fruit bar-she loves, or donuts, or yogurt-her favorite, anything chocolate-just milk will not touch dark, and they say chocolate is bad for cats-i don't let her have much she has been have a little bit her whole life and vet says she is great health, she loves puddings, pies, toast and jelly, not honey, loves little debbies, oatmeal with brown sugar, cream of wheat with brown sugar, and likes sweet tea, no one could fool me in believing she can't taste sweets. she can be in the back of house and just as food is done and i sit down, even before i start eating, she is in here ready to eat with me. she eats some of everything i eat. i have one cat that likes butter. i eat the eggs and she licks the plate of any butter that is left or licks plate after grilled cheese. .
Reply | Report Abuse | Link to thisso, i don't know where they got there info or if my cats that i breed are just supper unusual. I am a siamese cat breeder. well, happy times all cat lovers. my sweet eating cat will be 11 on sept 24th. happy early b-day spartesia grundelia :-)
That's because there isn't a taste bud for spicy, which is why if you stick a hot pepper in your eye it will burn just as much or more as if you stuck it in your mouth. Unless of course the entire human body is covered in taste buds.
Reply | Report Abuse | Link to thisThat must mean that my cat isn't a cat because when he sees some coke or soup or bread, he doesn't bother but when there's some jam or sweets on the table he instantly starts licking it.
Reply | Report Abuse | Link to thisHad a rescued Maincoon that turned out to have a strong liking for ice cream, grazed doughnuts and twinkies.
Reply | Report Abuse | Link to thisI used to have a black cat that would run by in the morning covered in white powder, only to discover the powdered donuts on the counter had been eaten. I know the article suggests that this is just the beginning of the research, but it is interesting about the genetic differences about taste. If we can crack these codes in the universe, who knows, maybe someday we WILL have wallpaper that tastes like Schnozzberries, and capsules that taste like four-course meals!
Reply | Report Abuse | Link to thisKeep up the prodding, science!!
I call BS on this. My cat will knock you down for ice cream and chocolate. She won't eat any meat off the table either, and she has hunted, so it's not like she only eats cat food.
Reply | Report Abuse | Link to thisThank-you null. Cat people do read Science.
Reply | Report Abuse | Link to this