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Is It Safe To Feed My Dog Garlic?

Updated: Jun 17, 2023


garlic cloves

If you’re a dog owner who wants to improve their companion animal's health through diet, and you’ve read about foods that are toxic to dogs, you’ve no doubt come across posts that have mentioned garlic.


In this post, I’ll attempt to break down the debate, clarify why there are opposing sides on the issue and offer context behind the oft-quoted study on garlic.


Garlic: A Divisive Issue In Dog Care


The issue of giving garlic to dogs is a matter of fierce debate among owners and many veterinarians, with many conflicting professional opinions. It can be confusing for dog owners when high profile holistic veterinarians, such as the esteemed Dr Karen Shaw Becker, author of The Forever Dog, tell them that garlic is safe, while the American Kennel Club states explicitly that it is highly toxic.


The reason for the debate is a small scale, commonly cited Japanese study that was published in the American Journal Of Veterinary Research in November 2000 that showed haematological changes (blood cell alterations) in dogs given garlic extract. The results of this study have since been repeated time and again by many veterinarians, and are the basis of the opinion that garlic is toxic to dogs.


Garlic Toxicity: Thiosulfate And Dogs


Garlic and onions contain a compound called thiosulfate, which in large enough quantities can form clumps around haemoglobin and cause red blood cells to rupture. The question, however, is how much thiosulfate needs to be present in order to cause these changes to occur.


It is common knowledge that there are plant foods that contain compounds known poisonous to humans - but we still eat them because the quantities consumed pose no risk and the foodstuff may even provide health benefits.


Almonds, for example, (both bitter and sweet) contain amygdalin - a compound that is converted into cyanide. If you were to eat an enormous quantity of this nut, it may make you quite unwell, though in small amounts, the amount of cyanide in our bodies does not cross the threshold of what could pose us any kind of harm.


Many veterinarians believe that garlic in small doses can offer health benefits to your dog without posing any kind of risk to their health. The question, therefore, is why do so many veterinarians believe that any quantity of garlic is toxic.


Point Of Conflict: Context In Scientific Literature


Whenever you hear about scientific studies on topics that are of direct relevance to you, you should always read the study yourself and weigh the findings - or look for an analysis of the findings elsewhere, if these things go over your head.


One reason for this is because, as The Economist recently revealed, as many as 50% of scientific studies submitted to peeer reviewed journals are fraudulent - that is to say that results are falsified in order to support desired conclusions.


Another reason to read the studies for yourself is that many of those that are legitimate present data that has been gathered from biased methodologies that enable the researchers to mislead the reader when presenting their conclusions.


This is commonly done in studies that are funded by organizations with a vested interest in improving the image of a particular product, such as studies funded by the tobacco or meat industries.


For example: in the United States, one study on beef was able to show that red meat can lower cholesterol, contradicting the known fact that the opposite is true. How was this done? When you read the method of the study, it turns out that the control group was fed a diet of Twinkies.


What To Look For When Weighing Scientific Findings


While I do not profess to be an expert on identifying fraud within scientific literature, the time spent reading medical studies for fun has allowed me to pick up on some key things that you should look for when judging the plausibility of scientific findings..


  1. Funding


There are many studies out there that are conducted by established universities and research facilities whose name lends credibility to the findings. However, most universities and research facilities rely on the private funding that they receive for conducting studies for third parties.


In many cases, where the third party stands to improve their profit margin by improving the image of a certain product, they will expect the method of the study to be favorable to their interests. In order to judge whether a study can be trusted, you should always carry out a little research on who funded it.


  1. Scale


In scientific studies, scale really matters if you want to be able to prove a point rather than simply indicating a need for further investigation. This is due to the fact that the smaller the scale, the greater the margin of error - in a study involving just a handful of subjects, slight anomalies can have a major impact.


Larger studies are more informative, and they are less influenced by individual subjects. Unfortunately, as scientific studies are very expensive, many studies on issues of dog health are carried out on a very small scale.


  1. Methodologies


You should always pay attention to the method that was used to obtain the results, in order to determine whether the study was designed in a way that would allow the researchers to present misleading results. A study that proves the efficacy of a product by comparing it to a control group receiving a product that is likely to cause greater harm is simply not reliable.



Let’s start by saying that while I couldn’t find any motive for bias in terms of the research funding, the method was highly questionable and not indicative of anything that anyone in the real world would possibly try to replicate when trying to provide their dog with the health benefits that garlic can offer.


Method


Eight healthy mixed breed dogs were force fed garlic extract for 7 days and changes to their blood were monitored. Dose? 1.25ml of garlic extract per kg of bodyweight, equivalent to 5g of whole garlic per kg of bodyweight.


That’s the equivalent to a dog of Yoto’s size (27kg) being forced to ingest 136g of garlic (around 45 cloves or 3 whole bulbs) per day, for 7 days straight - an amount of garlic that no one in their right mind would consume themselves, let alone give to an animal.


Given the specifics of the study, it is hardly surprising that it resulted in toxicity. In addition to this, while the dogs that were abused in this study did develop anemia, it’s important to note that after the study ended, they all recovered.


Is It Safe To Feed My Dog Garlic?


The study showed that feeding dogs enormous quantities of garlic is likely to result in toxicity and lead to anemia. But are small doses of garlic safe for dogs?


Like many things that are good for us, consuming abnormally large quantities of almost anything can cause harm, rather than conveying the health benefits intended - an example would be that supplements containing green tea extract can lead to liver cirrhosis when consumed in large quantities, or when combined with drinking green tea. Does that mean that green tea is toxic and should be avoided? No, it’s just proof that you should never get carried away and overdo it. Less is more, as they say.


Contrary to the viewpoint that has been spawned by the aforementioned study, there are many veterinary professionals that have years of experience in recommending garlic supplementation to patients, without having ever seen hematological side effects, such as Dr Karen Becker, the author of the Forever Dog.


Garlic in small quantities is not toxic to dogs and has many health benefits. It is only in excessively large quantities that it poses a health risk.


Dr Becker recommends the following daily doses:


  • Dogs weighing 10 - 15lbs (4.5 to 7kg): ½ a clove

  • Dogs weighing 20 - 40lbs (9 to 18kg): 1 clove

  • Dogs that weigh 45 - 70 lbs (20 - 31kg): 1.5 cloves

  • 75 to 90lbs (33 to 40kg): 2 cloves

  • 100lbs and over (45kg and over): 2.5 cloves



References

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