Hey, welcome to Science Stuff production of iHeartRadio. I'm Hora Cham and today we are answering the question why can dogs eat chocolate? Will a Hershey's kiss be the kiss of death for your pooch? Or will a roller bar make your dog roll over into the grave? How toxic is chocolate to dogs? Why is it toxic? And when do dogs evolve this intolerance. We'll talk to a couple of veterinary toxicologists and to one dog geneticis to get
to the nougat center of this question. So come along as we answer the question why can dogs eat chocolate? I promise the answer won't be rough.
Hi.
Everyone, you've probably heard that eating chocolate is bad for dogs. People, it seems, can eat a lot of chocolate and chocoholics, I'm looking at you, but it seems to be dangerous or even potentially deadly for dogs. Now, most people seem to think that's because chocolate has a chemical in it that is uniquely toxic for dogs, but that is perfectly safe for humans. But as we'll learn today, that's not really true. First, we'll talk about how serious it is
if a dog eats chocolate. Then we'll talk about what chocolate does to dogs, and in the last segment, we'll ask an evolutionary biologist to tell us when scientists think this sensitivity evolved in dogs and spoiler alert, it may be some humans's fault. Okay, the first topic is how serious is it if a dog eats chocolate? So the first thing I did was call an emergency hotline, not because my dog had eaten chocolate, but to talk to one of their experts. So here's my chat with doctor
Renee Schmidt. Thank you for calling Pet Poison Helpline, a twenty four to seven animal poison control center.
If you are a pet owner, please press one.
Well, thank you doctor Schmidt for joining us.
Yeah, thank you so much for having me. I'm doctor Rene Schmid with Pet Poison Helpline. I'm the director of Veterinary Medicine and senior veterinary toxicologist, so I help educate pet owners as well as venary professionals on anything toxin related, as well as working with our staff internally.
Amazing.
Can you tell us about Pet Poison Hotline.
We are a twenty four to seven animal poison control center and so pet parents as well as veterinary professionals can call us, and if an animal has been exposed to something that may be toxic, we can assess it to determine if the exposure is going to be a concern for that animal or not. While the vast majority of calls we receive are end dogs and cats, so we can help with any species of animal and with anything that they get into. So we had a sloth
that's got into a cleaning chemical. We had a goose not too long ago that got into marijuana. You name it, and we've probably gotten a call on it. And we're staff twenty four hours a day.
And you said you're all over the country, so we.
Take calls all over the country and really all over the world. So the vast majority of our calls are from the United States and Canada. We also take calls from the Caribbean and Hong Kong and other countries throughout the world.
Oh my goodness, And how do you cover twenty four hours? Are you just constantly on calls.
Yeah, so we're a busy place. It's amazing how many animals get into things that they couldn't. We have employees who have ships throughout the day and evenings so that we always have veterinarians and technicians who are on and ready to take calls at any time.
How often do you get calls about dogs eating chocolate?
It's our number one call, It's our most common call. I've been here for twelve years, we've been in business for twenty one years, and it's been our number one toxin every year since we've been keeping track. We always look back the year prior to see what was our top toxins, and chocolate always I always say it takes the cake. It's always number one. You know, if you think about it, so many households have chocolate in them.
Maybe we're cooking with it, we're buying it in different products or candy and chocolate itself, or maybe it's in brownies and cookies for the holidays, we're gifting it, and so maybe it's under the tree, or it's sitting out at parties and you know, activities and social events. So it's something that is really a commonplace in so many households that it smells good, it tastes good, so dogs are naturally kind of drawn to it.
You say it takes the chocolate cake.
Yes, that's right, it takes the chocolate cake, for sure.
So, yeah, there are a lot of dogs out there eating chocolate. Another animal poison control center would run by the American Society for the Prevention of Cruelty to Animals or ASBCA, reported that they receive about seventy six calls a day of dogs eating chocolate, which translates to about twenty seven thousand, seven hundred and forty cases a year. Next, I ask sector SMIT, what happens if a dog eats chocolate? What are some of the symptoms dogs might exhibit if they eat it.
Yeah, so symptoms are similar to over simulation. So they might be a little bit restless, they might be pacing, panting that maybe agitate a little bit. They can have a high heart rate, They can have a high blood pressure depending on how much they ingest. They can have heart abnormalities in rhythm abnormalities. Vomiting is certainly a common one, as well as maybe some loose stool, and in some cases it may not even be a toxic amount that
they get into. The can have a risk for pincreatitis, which is just that inflammation of the pancreas when they get a high fat meal, and because of the richness of the chocolate, product itself, it could be enough to cause that to flare up. So thinking about our dogs that are more sensitive to pincreatitis, So the miniature Schnauzers and Yorky's some of those breeds, that may be something we have to be even more concerned about, even if they didn't get into enough to cause a toxic concern.
Oh wait, it's also the fat content.
Yeah, sure can be. So it depends on the amount that they get into. Dogs can tolerate a hershey kiss, but who wants to stop it just one? And so it's you know, when they get into that large handful or the bag, that can definitely be more problematic and cause that flare up.
Now would you see that immediately or is that more of a long term concern.
So stomach sign so vomiting and diarrhea and loose stool, that's something that we can see within a few hours, the true and a development of pancreatitis might actually be seen maybe later on twelve to twenty four hours or even a day or so later.
That's right.
Eating chocolate can be serious for dogs. It can cause heart problems, high blood pressure, it can affect the nervous system and even cause seizures. According to the Cornell College of Veterinary Medicine, drinking as little as half a cup of chocolate milk can be deadly for an average chihuahua, But according to doctor Schmid, not every call they get is life threatening. You said it's your number one call. I guess how would you break down those calls? Are
most of them pretty serious? Are some of them like, oh, they ate a kiss or a small bar and they're probably okay? How would you break that down?
That's a great question, And I would say that it's really fairly evenly spread out to being not really an issue. Fortunately, so many pet parents understand that chocolate is concerning to their pet and they shouldn't get into it. So I would say that it's a really pretty fairly evenly spread between a mild or low concern. Maybe they just ingested one chocolate chip cookie, and it's a labrador, it's a large, free dog, and so probably not going to be a
big issue. But then we get this past Halloween, we had a dog that ingested over six and a half pounds of chocolate in one setting.
Oh my goodness, how did that dog get into six pounds of chocolate? Was it they just had a chocolate factory, or they had.
Their Halloween A family had their Halloween candy out because it was Halloween Day or the day before, and it was in an area that the dog was able to get to and the owners weren't home at the time, and he helped himself.
Well, it just opened up all the wrappers and everything.
He ingested a lot of the rappers. A lot of the rappers were ingested and chewed him and kind of broke them open.
And yeah, oh my goodness, yep, dogs love chocolate. Don't even eat the wrappers, all right. This made me curious if doctor Schmid ever gets calls about other animals getting poisoned by chocolate. You mentioned other animals. Do you get calls about other animals like cats? And what are some unusual animals that you've had calls about chocolate?
So we do.
We get calls on every species, and the vast majority of the calls we receive are going to be dogs and then cats, And it makes sense because they're around humans more. They just have more access to the things in the household. We certainly get calls from chocolate on other species of animals to you know, usually something like a rabbit or a ferret, or maybe a chinchilla.
That's incredible. It's a little bit ironic that you would have a bunny getting poison patrol call about chocolate.
Yeah right, Hopefully that rabbit didn't eat any of the chocolate bunny at easter.
So chocolate effect other animals too, including cats and rabbits. And if you search the scientific literature, you'll find reports of chocolate poisoning in cows, bears, and even coyotes. So what's going on here? What is it about chocolate that makes it so harmful to so many animals except apparently humans. When we come back, we'll talk to another expert on what it means for something to be toxic and how that affects what your pet can eat.
Stay with us, we'll be right back. Welcome back. Okay.
We learned that dogs definitely like chocolate, but that it's not good for them. We also learned that it's not good for other animals like cats and rabbits and even bears, and yet people seem to be fine with it. In fact, some of us eat it a lot. So what's going on?
To answer this?
I reached out to doctor Bob Poppingaate, a professor of veterinary toxicology at the University of California at Davis who runs the toxicology lab at the California Animal Health and Food Safety Laboratory. He was just a few days from retiring, but he took the time to talk to me. So here's my conversation with doctor Bob Poppingate. Well, thank you doctor popping Gate for joining us.
Pleasure to be here.
So today we're trying to answer the question of why dogs can't eat chocolate, and I thought maybe we would start by taking a step back, giving people a general idea of what it means for something to be toxic to an animal or to us.
Well, pretty much anything is toxic. Key is how much is actually ingested. One of the tenants is that dose makes the poison, So it's all about the inherent toxicity of a compound, and also how much is actually ingested by a dog or a person or a child, whatever. Some things are more toxic inherently. If you ingest enough water, that can be toxic.
Okay, According to doctor Popingay, there are two variables here, how inherently toxic something is, In other words, how bad it is for you and how much of it you eat. For example, cyanide is bad for you even if you only eat a little of it, But water, which is normally good for you, can also be deadly if you drink enough of it. Here's how doctor Popingay explains it. What do you mean by everything can be toxic?
Well, it gets back to the inherent toxicity of a compound. So, you know, there are certain vitamins that are required. We ingest a certain amount of vitamin E or vitamin D per day, but in excessive doses of vitamin E can cause adverse effects. So it just depends on the individual compound. But in sufficient doses, anything can be toxic to our bodies.
Now, what makes something more inherently toxic than others?
You know, it gets back to sort of the unique characteristic of a compound and our ability to handle that compound.
These things do they generally interfere with how the body works. Are these things burning a hole in my stomach or well.
There's a lot of different ways that a given chemical can cause toxicity or adverse effects. You know, it can affect our enzyme systems, it can affect neurotransmission, the neurotransmitters that are released by our nervous system. It can block certain body signals. It can damage cell membranes through what's called oxidative damage, some things like corrosives. It's going to cause damage to the mucosa, the upper gi track. So a lot of different ways that chemicals can cause adverse effects.
Well, it seems that almost America, we can eat anything, all right, So something can be toxic for lots of reasons. There are almost endless ways in which chemicals can mess with the signals in our bodies or directly damaged cells or membranes. So now the question is what makes chocolate. So then specifically for dogs, how bad is chocolate for dogs?
Well, that is very common intoxication in dogs. It's one of the top things that veterians have to deal with. But dogs can tolerate a certain amount of chocolate. The chemicals in chocolate that cause problems, they're related and they're called methyl xanthines. One is called theobromine, the other's caffeine. So people are probably more familiar with caffeine, which is
also in chocolate, so we have both. People are less familiar with the theobromine, which is related to caffeine has the same effects, but the theobromine is at higher concentrations in chocolate products. Those are the two compounds that cause problems.
Okay, this is kind of a key point. The ban chemicals that make chocolate bad for dogs are caffeine and theobromine, which is basically another form of caffeine. It's not some exotic toxin or chemical. It's basically what we all drink every day when we drink coffee or tea. Now does caffeine or theobamine have some kind of special effect on dogs that they don't have on us? Not really, Okay, So then what do these compounds do to the dog.
Let's say a dog eats a bunch of the baking chocolate or stip some coffee.
What is it going to do to their.
Body once it's absorbed. The theobromine caffeine effect the cardiovascular system and the nervous system. So you know, if you drink three or four cups of coffee in the morning, you get a little bit nervous, your heart rate can go up. These compounds are also diuretics, so you increase your own production. That's why you have to go to the bathroom after a few cups of coffee. But the primary adverse effect is on the nervous system and our hearts. So the heart rate goes up, you get a little
bit excited. With a really large dose, you could have seizures. The most serious consequence is cardiac a arrhythmius, so your heart rate changes. Of the dogs, the dogs are people or any other species or animal that get into a sufficient amount.
Like the same effect caffeine has in us it's having on the dog. In other words, caffeine and theobromine have the same effect on us as they do on dogs. These chemicals are as toxic to them as they are to us. But we drink coffee and eat chocolate all the time. So how does that make sense. Well, the answer is that while humans and dogs react to caffeine and theobromine in the same way, there are differences that affect our exposure to them. The first one is that dogs are smaller than us.
Well, it gets back to how much the dog actually ingest on a body weight basis, So we could be intoxicated by these products as well if we ate enough of them. These compounds can't be toxic to us, So if a child got into baking chocolate and ingested half a package, you might have a very sick child.
Yeah, so most dogs are smaller than us. For example, a tiny shoe walla weighs about four pounds, so a cup of chocolate milk to them would be the equivalent of an average American eating ninety spoonfuls of cocoa powder in one city. If you did that, you'd be pretty sick too. The second difference that affects how much chocolate dogs eat if the dogs don't seem to have a lot of self control.
The other thing about dogs, why it's a problem. If you have a dog, you know, they're very indiscriminate eaters. They eat things and then ask questions later. If it's edible, it's going to be very attractive for a dog. So if they have access to a pan of brownies, they're not going to stop with one brownie. You know, they're going to clean up the entire pan of brownies. So cats are about as sensitive to the chemicals and chocolate as dogs are. But cats are not going to sit
there and eat a whole package of baking chocolate. Dogs if they have access to something, they don't have any self control, so they will eat everything there that's in the package, whereas a person. You know, baking chocolate is fairly bitter, so maybe a child might taste a little bit of it, but they're not going to sit there and eat the whole package.
I don't know.
I know there's some chocoholics who might dig into that whole bag, right right, Okay. The last difference between people and dogs is the dogs don't metabolize theobromine as well as humans. Here's how doctor Schmid explains it.
Yeah, so in toxicology, we talked about a half life, and the half life is the length of time it takes the body to rid itself of half of the amounts of that toxic component or what substance or drug or what have you. And so the half life, the amount of time it takes for dogs, in particular, to rid the body of the theobromine, is much longer. In dogs, it's about seventeen and a half hours, whereas in humans
it's just a few hours. And that definitely contributes to the toxic effects that we see in dogs, and it also contributes to the length of time that we see or the duration of time that we see those effects.
So there is a difference between dog and human biology. In terms of chocolate, the abromine and caffeine have the same effect on us, but it takes longer for dogs
to break down those chemicals, so the effects last longer. Now, most articles you read online will tell you this is the main reason dogs can't eat chocolate, but actually both experts agree that much bigger factors are a that dogs are smaller and b that they can't stop themselves and will eat huge amounts of chocolate if they have access to it. Okay, the last question I asked doctor Poppingay was now, why can't dogs metabolize these compounds as well as humans? What's the difference?
They have different enzymes in their liver that break down compounds. Every species says a little bit different. A good example of a species difference is cats. You should never give a set of metaphen or tilen all to a cat because they can't metabolize the compound like we can or dogs can. So cats are very sensitive to the adverse effects of a set of menifin.
I see, so it's genetic.
It's genetic in the sense that it's a species difference.
Why do you think there are these differences in species.
Ah, that's a good question. That's kind of a evolutionary question, and it probably goes back thousands, if not tens of thousands of years.
Okay, when we come back, we'll actually try to answer this question by going back in history with a dog geneticis to where dogs came from. Don't go anywhere, we'll be right back.
And we're back. Okay.
The last person I talked to was doctor Maya Arrand, a professor at the University of Copenhagen. Here's what she does.
So my name is my aunt, and as well as being a vet with a specialty and oncology, I'm also a researcher in genetics and focus a lot on comparative genetics, looking at genetics between humans and animals. And then I've also worked a lot with dog evolutions, looking at bay see how wolfs goot domesticated into dogs as we know them today.
Now, the reason I talked to doctor Arrand is that I wanted to know why dogs can't process chocolate as well as people can. And it turned out that doctor Aaron can paint a pretty interesting picture of why dogs might have ended up that way and spoiler alert, it might all be our fault.
Okay.
I started off by asking her to recap what we know about where dogs come from. So can you give us a brief history of dogs, like where did they come from?
So dogs really originated from the gray wolf and they were domesticated, well, actually, no one really knows exactly, but as early as forty thousand years ago. Some say, oh, it's definitely just one event that happened twenty three thousand years ago in Siberia, but there's also suggestions that dog
domestication has been happening several places around the world. Somewhere along the time, there's been some wolves that were maybe less fearful of humans and have sort of been more curious, and those are the ones that have sort of been closer around humans. There's also a theory that they have maybe been interested in scavenging, so scavenging around the places where humans have lived, and these factors sort of led
to humans and wolves being in closer proximity. And then the exact sort of domestication, if it's been humans taking wolf puppies because they look cute or how this happened is not exactly sure.
Interesting so at some point. The first dogs were just domesticated wolves, and so they look like wolves, but now they look like Chihuaha's and poodles.
Yeah, so there has been a lot of heavy selection towards the dogs that we known in today, and yes, originally the dogs that existed many thousand years ago, they have looked or resembled much more the gray wolf as we know it today. But what really happened is, obviously people have selected for dogs to be used for different purposes. They have chosen dogs that fitted to a certain purpose and tried to breathe these together.
Okay, so only up to about twenty to forty thousand years ago, there were no dogs. There were just wolves. And then one or two kinds of wolves started hanging around people and a best friendship was born. So every dog today signed this belief came from those first wolves that were friendly to humans. So how do you go from a huge, fierce looking gray wolf to poodles in chiwalas?
Significantly? I think around two hundred years ago, aways sort of the first kennel clubs we're established, and their people say, now we're going to create these different breeds of dogs, and we have to have pedigrees so we can sort of be sure that we're only breeding dogs from the same breed, and there we've sort of selected very stringently towards the breeds that we have today. This has had some consequences, and it doesn't mean that there is a
lot of inbreeding within certain dog breeds. And there's also been some sort of negative health consequences that we don't really see in their ancestors, as in the gray wolf.
Oh so the big diversification that we've seen dogs today only maybe mostly happen in the last few hundred years.
I mean, if you look at sort of old paintings, you can definitely see there's sort of different dog phenotypes. But now we have these really different breeds. That's really something that's only happened very recently. And what happens every time you sort of do this selection is you create what we call a genetic bottleneck, is where you have only a small amount of genetic material that goes further
to great and new population. And this does I mean that you will have a lot of sort of inbreeding within different dog breeds.
What you're saying makes me wonder if one of those negative consequences could have been an intolerance for chocolate.
So that's a really interesting question why dogs don't tolerate chocolate very.
Well, Okay, this is where it gets interesting. Doctor arend has been a part of several teams that have sequenced the dog genome. That means they catalog the genes in dog DNA, and there are two studies that tell an interesting story about dogs and potentially chocolate. In the first study, doctor Aren't and other researchers compared the DNA of dogs to the DNA of wolves. Here's how she describes it.
Yeah, so that's really my favorite part of my research because it was such a clear signal we saw some years ago. We decided to look at the differences between wolves and dogs. So basically, sequence the pool of different wolves from different parts of the world, and then sequence of different dog breeds and then try to look at differences. And what we could see is, obviously we found a
lot of signals that were related to newer developments. So this suggests that obviously there's difference in behavior and how the brain functions between wolves and dogs.
All Right, the first difference they saw between dog and wolf DNA was in genes related to their brains, and this makes sense because we know that one big difference between dogs and wolves is that they behave differently. Wolves are wild and dogs are domesticated. But then they saw another clear difference.
But one of the sort of really strikingly clear signals we also saw was related to the digestion of starch. We know that wolves are really cardivores, so they tend to eat meat only. So there are hunters in the wildlife and they will mostly eat and hunt different types of prey. And we look at dogs, it seems like they are sort of closer to on their wards, so they can also tolerate other substances, or they can also sort of feed on starch containing foods.
Okay, what they saw was that the genes of dogs were also more adapted to eat starches, meaning that when they were wolves they only ate meat, but once they became dogs, their digestive system changed so they could eat basically carbs like rice and wheat. What does this mean?
So what we could see in our research was we really found relatively strong signals that suggested that dogs have not only been domesticated sort of in relation to their behavior to living humans, but actually they also seem to have adapted to the diet that we eat.
Does that mean that dogs can digest sugars more?
Yes, that's definitely our theory.
What doctor rn is saying is that as dogs became dogs and started living with humans, they adapted to our or diet, and that meant being more omnivorous and being able to eat a wider range of foods, including perhaps chocolate. I wonder if this adaptation being able to eat more sugars has made them more prone to eating the chocolate we leave around, Meaning like, if I leave a chunk of chocolate with a wolf, would the wolf want to
eat this? Maybe not because it wouldn't taste good or wouldn't have that drive to eat it.
What do you think?
So that is a really good question. One of the things we did see in our data originally was some of the taste receptors in the tongues, and there potentially could be some differences there, But it's definitely something that would make sense that as part of this adaptation, that maybels actually think that this chocolate didn't taste good and dogs would be more sort of interested in it. But again, that would be a very theoretical question. I don't think anyone's sort of shown that.
Okay.
The second interesting thing doctor arn has found when looking at the DNA of dogs is that actually dogs do have a gene that can help them metabolize chocolate or theobromine.
One of the interesting things we saw in our new reference genome was we found a duplication, So that means that instead of just having one copy of a gene, you can have multiple of a gene called SIP one A two, and that is a gene that encodes enzyme that's important for digesting what called cenobiotics, for instance, theobromine
that the body doesn't produce itself. And we can see that based on the twenty seven other dogs we had in our data set, that some dogs have two copies of the SIP one A two and then some dogs would have up to five copies.
So dogs have multiple copies up to five of a gene that would produce an enzyme that would help them break down theobromine, the chemical in chocolate. They can make them sick, but for some reason the gene doesn't get used.
Specifically, it's SIP one two that's been associated with theobromine digestion. And then there's actually also one that's called sip to E one I believe, which also been linked to theobromin digestion. And the dogs have both of these genes, so it's
not like they're missing one or it doesn't exist. And that's why, Well, if they have the genes that required, why do we eat then see that they get this chocolate toxicos is more frequently than you would see, you know, the species, And that's maybe down to the way the genes are expressed, so that maybe just not expressed in a high enough amount.
So they have the gene to process theobromaine. We just don't know why they don't express it enough to help them.
Yeah, I guess that would be the theory that they're not expressing it high enough or fast enough as they are in humans.
Doctor arn says that a possible theory is that dogs have the genes to break down the chemicals and chocolate, but maybe changes in other parts of the DNA are preventing these genes from expressing themselves to actually make the enzymes to digest chocolate. One potential source of these changes could be the interbreeding that's happened in dogs over the last few hundred years.
So there have been people showing that there have been two sort of small genetic variants in the SIT one agen that we can see that occurrent dogs, and they have hypothesized that these genegrants made the one A two gene function worse, so when it was translated into enzyme, that enzyme wasn't as good as digesting deobromine.
So it seems like maybe a possible picture. We can't say anything for certain, but a possible picture is that dogs adapted to human diet, but something happened along the way that made them not adapt to theobromaine digestion, which kind of puts them in this bad spot where they're adapted to eating our food, but just not this one particular food. And so that's why it's such a problem today.
Yeah, I think probably that is pretty correctly.
Put In other words, it's because of us that dogs can and want to eat foods like chocolate, but along the way they might have lost been able to digest the chemicals and chocolate maybe also because of us and all the interbreeding we've done to them. So maybe the problem is we need to give more chocolate to dogs.
Yes, tell us, I said evolution doesn't happen over time, and for that selection to happen, there will be a lot of dogs that would not do well. Yeah, so I think the better idea is probably not to give dogs chocolate.
Yeah, we'd better for humans just to stop eating chocolate, or at least humans with dogs.
Well yeah, I'm not sure if humans should completely stop eating chocolate, but they should be more careful lenient around where dogs can get access to it.
That makes total sense, all right.
To recap, the answer to the question why can't dogs eat chocolate seems to be mainly the dogs are smaller than us, and they are which makes it easier for them to overdose on the caffeine, the bromine and fad in chocolate. And on top of that, they've lost the ability to quickly break down some of these chemicals, maybe because of us. So if you own a dog, be sure to put away or eat all your spared chocolate.
And that's just dogon good advice.
Thanks for joining us, See you next time you've been listening to science stuff. The production of iHeartRadio written and produced by me or Hey Cham, edited by Rose Seguda, Executive producer Jerry Rowland, and audio engineer and mixer Ksey Pegram and you can follow me on social media. Just search for PhD Comics and the name of your favorite platform.
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