Why can’t dogs eat chocolates? — Foods toxic to pets Why can’t dogs eat chocolates? — Foods toxic to pets – SOMETHING ABOUT SCIENCE

Why can’t dogs eat chocolates? — Foods toxic to pets

Scan of a Valentine greeting card circa 1920.

Photo credit: Wikimedia Commons

With the celebration of Valentine’s Day last week, some of you may have received flowers or boxes of chocolates from your loved ones. For those of you also lucky enough to have furry friends, share the love but not the chocolates! Read on to find out why.

Cocoa-based foods are very nutritious. Cocoa contains high amount of amino acids, vitamins, minerals, and fat that keeps our body full of energy. Nonetheless, cocoa products, including chocolates, are very poisonous to animals.

It is estimated that about 25% of pet exposure to toxic agents is by chocolates. Also, 80% of pet owners seeking aid for poisoning are dog owners (probably because dogs tend to explore things through mouth more than other animals). Chocolate poisoning for dogs is reported throughout the year, but holidays, such as Easter, Valentine’s day, Halloween, and Christmas, are especially dangerous times for pets, as chocolates tend to be bountiful in the houses.

By toxic, I mean VERY toxic; the pets can get seriously ill. In dogs, symptoms appear within 24hrs of ingestion. Symptoms include vomiting, diarrhea, increased urination, and progress to dehydration, cardiac arrhythmias, internal bleeding, heart attacks, seizures, coma, and then death.

Photo credit: Jonathan Reyes on Flickr

Photo credit: Jonathan Reyes on Flickr

So what makes cocoa products toxic? Cocoa beans are very rich in a compound called theobromine. They also contain caffeine, whose chemistry is very similar to theobromine, but to keep things simple, I will only discuss theobromine in this post. Theobromine can mess up the balance in the body in a couple of ways. For example, it can inhibit components of central nervous system (CNS) called adenosine receptors, which leads to CNS stimulation. It also increases calcium levels inside the cells, which can lead to tachycardia. It may also cause accumulation of an important chemical in the body called cAMP, which will affect many processes in the body, such as CNS and heart contraction.

de: Struktur von Theobromin; en: Structure of ...

Chemical structure of theobromine. Image credit: Wikimedia Commons

The darker (or richer in cocoa) the chocolate is, the more dangerous for pets, as it contains more theobromine. Cocoa powder and cooking chocolate contain the largest amount of the compound and are the most poisonous for animals. For instance, about 25g of cooking chocolate can be poisonous for a 20-kg dog.

So how come humans can eat chocolates? Compared to other animals, we can quickly and safely digest theobromine, so that the amount of theobromine in chocolates is not large enough to cause problems. We owe it to our enzyme cytochrome P450 in the liver, which metabolizes theobromine into harmless compound which then gets excreted out through urine in no time. For animals, theobromine is metabolized much slower, so that enough of the compound accumulates by eating chocolates. Thus the toxicity is dependent on the type of chocolate, the amount consumed, and the body size of the animal.

Cocoa is not the only food poisonous to our furry friends. Fruits of the vine (grapes, raisins, and sultans) are also emerging as a new concern for pet owners. Dogs can get kidney failure after consuming these fruits. Toxic dosage for fruits is not quite established yet, so that any amount should be considered toxic. Nevertheless, it is estimated that as low as 2.8mg/kg of raisins can cause kidney failure in dogs. The mechanism of toxicity in fruits is not known so far.

English: Wine grapes. Español: Uvas de vino ro...

Photo credit: Wikimedia Commons

Onions, garlic, leeks, and chives are also toxic to pets. All parts of these plants, in any form (raw, cooked, or dried) are poisonous, so be careful when giving out scraps off your plate. There are several toxic compounds in these plants, but the major one is called n-propyl disulfide, which leads to the damaging of red blood cells and causes hemolytic anemia in 1-5 days. (Rest assured, humans are resistant to n-propyl disulfide!)

Oh my, the list goes on. Avocado is toxic to pets, and so are macadamia nuts. Avocado triggers fluid accumulation in the lungs of animals, causing breathing difficulties and death. Macadamia nuts affect their muscles, digestive system, and nervous system.

Last but not the least, alcohol is deadly to pets. Even small amount of alcohol can lead to liver failure and death in animals. So do not give them alcohol as a joke!

Now that you know your pets cannot enjoy so many of the foods we love, aren’t you glad that you are human? Or are we really protected from the effects of theobromine (and caffeine)? The compound can easily cross placenta and may cause fetal malformation if the developing fetus has not made enzymes to detoxify it. Studies using rats showed that theobromine caused delayed development in fetus—not that studies on animals can always be directly applied to humans.

I don’t mean to scare you, but you should know that scientists are not 100% sure about the toxicity of theobromine to humans. But the common theme seems to be that anything eaten in large excess results in your body not being able to catch up with the breakdown of the compounds, and the build-up of these chemicals causes toxicity. (Remember my earlier post about alcohol metabolism?) So, eat food in moderation; don’t eat crazy amount of chocolates or drink gallons of coffee at a time!

So what CAN dogs eat? Consult your veterinarian or refer to some recipe books for dog treats.

Thank you for reading this post. Next week, I plan to discuss our potential benefit of eating chocolates 🙂

***Note: Although information here is supported by literature, food toxicity is complex and greatly varies from individual animal to animal. Please consult your veterinarian before making changes to your pet’s diet!

(If you enjoyed this post, you might also be interested in a blog post by Deborah Blum on the toxicity of chocolates.)

Grapes, raisins and sultanas, and other foods toxic to dogs
Some food toxic for pets
Theobromine and the Pharmacology of Cocoa
Recent advances in caffeine and theobromine toxicities: a review

Lynn Kimlicka

I am a scientist-turned writer and editor, who loves to read and write (more than doing experiments). I have a PhD in biochemistry and molecular biology, with a specialization in structural biology. My interests range widely, from life sciences to pop culture and arts to music. I am bilingual in English and Japanese.

18 Responses

  1. Karen says:

    I really like your blog Lynn! I like knowing the biochemistry behind common knowledge type stuff 🙂

  2. Jeanie says:

    Love this topic! Although Byron had told me about the chocolate issue for dogs before, it’s interesting to know the details behind it.

    • Lynn K. says:

      Thanks, Jeanie! I agree with you. It’s good to know “why” chocolates are not good for dogs. Then we will remember better and will not be tempted to share chocolates with dogs!

  3. caitlyn says:

    amazing info helped with my science fair project

  4. gsdfanatic says:

    This is a must read for all dog owners. I really appreciate the information here.

  5. Praba says:

    Thanks! This is really great and important for pet lovers.

  6. ChevalierdeJohnstone says:

    While this is good advice, it is not scientific. This is not how nutrition and biochemistry works. Tens of thousands of dogs have eaten grapes, chocolate, onions, garlic, caffeine and alcohol with and lived long and healthy lives with no discernable side effects. Because to some dogs these foods are poisonous, and because we don’t have any reliable means of determining in advance which dogs will be susceptible, pet owners are advised not to feed these foods to their dogs. That does not, however, mean that to all dogs these foods are poisonous.

    Wildly outrageous claims that chocolate or onions or etc. are deadly poisons to all dogs are unscientific and simply not true. Blogs such as this one, and the uninformed veterinary press which persist in communicating these outright falsehoods, do a tremendous disservice to pet owners and pets. When you make an unsubstantiated and obviously false claim that, for example, avocados and grapes are deadly poison to all dogs, then anyone who knows an avocado or grape farmer and has seen their dog eat pounds and pounds of fruit with no ill effect, or reads the label of any premium brand of dog food and likely notices that onions and garlic are listed as ingredients, is likely to think that there is no risk at all. In fact, if you purchased your pet from a breeder, I will almost guarantee you that the breeder habitually added cooked onions and/or garlic to your dog’s food. This has been standard practice among many breeders for decades. Dogs have also been eating grapes, onions, and avocados for a lot longer than human beings had any concept of the idea of “nutrition”. Likewise, every mammal, with no exceptions for canines, is capable of processing alcohol, at least in undistilled form.

    The facts are that not all dogs find every or even any of these foods to be poisonous. It is probable that in reasonable amounts by body mass the majority of dogs would not suffer any adverse effects from any of these foods; since we can’t experiment on the majority of dogs we can only extrapolate statistically from observed results; we can’t make any statements as to the veracity of scientific hypotheses regarding the majority of canines. The facts are that experimental evidence indicates that some dogs do find some or all of these foods to be poisonous, and it is also the case that there is no safe and reliable means dog owners can use to determine if their dog will have an adverse reaction. Therefore the precautionary principle bids us avoid feeding these foods to our dogs rather than take the chance that a bunch of grapes or a piece of chocolate might kill them. However, it is highly likely that any particular dog can eat as many grapes or chocolates as it wants and only suffer the adverse effects of getting fat, and possibly of tooth decay.

    I would like to strongly encourage the author of a blog called “Something About Science” to strive to be accurate and scientific in writing articles such as this. Wild, unsubstantiated, experimentally unproven claims are not scientific and are quite likely to do more harm than good, because readers will eventually figure out that the claims are unsubstantiated and are likely, then, to ignore the good advice buried herein.

    Finally, readers should know that “not-for-profit” is not the same thing as “not making money”, and since the ASPCA began warning dog owners about the dangers of various foods in the 90s, patronage (for which you are charged a not insignificant fee) of the Animal Poison Control Center has skyrocketed. The ASPCA is a wonderful organization and does great things, but like any organization it has an incentive to encourage you to use its services.

    • Lynn K. says:

      Thank you for your insightful comment. I enjoyed looking at the topic from a different angle.

      I have taken information from the literature, but of course what is published in scientific journals does not necessary be true (or even “scientific,” as you pointed out). Published food toxicity in pets are mostly case studies, and molecular studies showing the mechanism or proving the toxicity are far behind. You also have a great point that the observed toxicity greatly varies from one individual to another.

      Taking your points into account, I have now added a disclaimer at the end of the post telling the readers that toxicity greatly varies and that they should consult their veterinarians before changing the diet of their pets.

      In general, there are discrepancies in many areas of science. As a matter of fact, I think that the whole point of science is to discuss and argue different observations or interpretations, with the goal of slowly approaching the truth. This is beyond the scope of this blog and I want to keep things simple so as not to scare readers away from science or confuse them, but I’m glad you brought it up! I hope I can make this post more informative and “scientific” by going into molecular details of the metabolism!

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