How Much Garlic is Safe For Dogs

No one likes to feed something toxic to their dogs. Not the nutritionist, not the dog parent, and certainly not the vet. One ingredient that has been controversial more than others is garlic.

I weighed in on garlic three years ago, but it’s recently come up again. So I thought I might elaborate because, this time, a vet dermatoligist was asking. This article summarizes the studies and provides a complete reference list. In addition, I have translated the levels of garlic that are safe and the levels that are toxic.

Initial Study on Garlic Toxicity

The initial study research question was as follows: “To determine whether dogs given garlic extract developed hemolytic anemia and to establish the hematologic characteristics induced experimentally by intragastric administration of garlic extract” (Lee, et. al 2000).

The study was on 8 dogs. The abstract explains:

 4 dogs were given 1.25 ml of garlic extract/kg of body weight (5 g of whole garlic/kg) intragastrically once a day for 7 days. The remaining 4 control dogs received water instead of garlic extract. Complete blood counts were performed, and methemoglobin and erythrocyte-reduced glutathione concentrations, percentage of erythrocytes with Heinz bodies, and percentage of eccentrocytes were determined before and for 30 days after administration of the first dose of garlic extract. Ultrastructural analysis of eccentrocytes was performed.

Results: Compared with initial values, erythrocyte count, Hct, and hemoglobin concentration decreased to a minimum value on days 9 to 11 in dogs given garlic extract. Heinz body formation, an increase in erythrocyte-reduced glutathione concentration, and eccentrocytes were also detected in these dogs. However, no dog developed hemolytic anemia.

Conclusions and clinical relevance: The constituents of garlic have the potential to oxidize erythrocyte membranes and hemoglobin, inducing hemolysis associated with the appearance of eccentrocytes in dogs. Thus, foods containing garlic should not be fed to dogs. Eccentrocytosis appears to be a major diagnostic feature of garlic-induced hemolysis in dogs.

The next logical question one would have, is just how much garlic are they talking about in this study? For those who need a little help with math:

Toxic Levels of Garlic in the First Study

For the 5 g of whole garlic/kg dosage:

For a 20 lb (9.07 kg) dog:

• 9.07 kg × 5 g/kg = 45.35 g of whole garlic
• Assuming an average garlic bulb weighs about 55g, this equals approximately 0.82 bulbs (about 4/5 of a whole bulb)

For a 40 lb (18.14 kg) dog:

• 18.14 kg × 5 g/kg = 90.7 g of whole garlic
• This equals approximately 1.65 bulbs (about 1 and 2/3 bulbs)

For a 60 lb (27.22 kg) dog:

• 27.22 kg × 5 g/kg = 136.1 g of whole garlic
• This equals approximately 2.47 bulbs (about 2 and 1/2 bulbs)

To be clear, even humans do not eat that amount of garlic every day.

The media sensationalized this study, leaving out the details of just how much garlic was toxic.

True reporting would have stated that high levels of garlic is toxic. But all the headlines ran with is “garlic is toxic for dogs”. The saving grace is in the details but details don’t increase traffic so that piece of information was conveniently left out.

At that time, garlic was a common ingredient in kibble and so companies, under pressure from dog parents, had to revisit their formulations.

As you can imagine, this caused a commotion in the pet industry, which led to additional studies.

Follow-up Study on Garlic Toxicity

The follow-up study (Han Wen-hai et al., 2008) focused on the long-term toxicity of selenium-enriched garlic in dogs. Dogs were fed varying doses of garlic (3.00 g/kg, 1.50 g/kg, 0.75 g/kg) over 12 weeks. The study found that at the highest dose (3.00 g/kg), dogs exhibited symptoms such as vomiting, decreased appetite, increased serum total bilirubin, and changes in thymus and spleen coefficients. However, no obvious toxic reactions were observed at a dose of 0.75 g/kg, indicating a threshold below which garlic did not cause significant harm .

This study not only looked to see a toxic level, but it also looked to see if there was a safe level. For those in research, the research question is key in driving how the research is conducted. It was very clear in its conclusion as follows:

“RESULTS: Dogs in the high dose group vomited intermittently, and appetite was decreased. Serum total bilirubin was obviously increased, the albumin lowered, the coefficients of thymus gland and spleen went up. No other toxic reactions were observed. CONCLUSION: The selenium-enriched garlic was a mild alimentary tract stimulant with obvious increase in the serum total bilirubin, at 30 times the clinical dose. The dose of 0.75 g/kg in dogs had no obvious toxicity reaction.”

The level that induced those reactions were fed high levels of garlic every day for 12 weeks.

For those that need a little help with math, what this level translates to in this study is:

Toxic Levels of Garic (Daily) in the Follow-Up Study

For the 3.00 g/kg dosage (where toxicity was observed):

For a 20 lb (9.07 kg) dog:

• 9.07 kg × 3.00 g/kg = 27.21 g of whole garlic
• Assuming an average garlic bulb weighs about 55g, this equals approximately 0.49 bulbs (about 1/2 of a bulb)

For a 40 lb (18.14 kg) dog:

• 18.14 kg × 3.00 g/kg = 54.42 g of whole garlic
• This equals approximately 0.99 bulbs (about 1 whole bulb)

For a 60 lb (27.22 kg) dog:

• 27.22 kg × 3.00 g/kg = 81.66 g of whole garlic
• This equals approximately 1.48 bulbs (about 1 and 1/2 bulbs)

Safe Levels (Daily) in the Follow-Up Study

For the 0.75 g/kg dosage (where no obvious toxicity was observed):

For a 20 lb (9.07 kg) dog:

• 9.07 kg × 0.75 g/kg = 6.80 g of whole garlic
• Assuming an average garlic bulb weighs about 55g, this equals approximately 0.12 bulbs (about 1/8 of a bulb)

For a 40 lb (18.14 kg) dog:

• 18.14 kg × 0.75 g/kg = 13.61 g of whole garlic
• This equals approximately 0.25 bulbs (about 1/4 of a bulb)

For a 60 lb (27.22 kg) dog:

This equals approximately 0.37 bulbs (about 1/3 of a bulb)

• 27.22 kg × 0.75 g/kg = 20.41 g of whole garlic
• This equals approximately 0.37 bulbs (about 1/3 of a bulb)

As you can see, a small amount of garlic has been shown to not have any toxic effects.

Read The Ingredients

How does this apply today?

You can visit any of the larger dog food companies, such as Purina, and see that Garlic oil is part of their ingredients.

I could easily find 20 other bags of kibble that show garlic as an ingredient but I invite you to do this search yourself. Or walk down your dog food aisle to make this same discovery.

In my own recipes I use garlic before I recommend something like fecal matter transplants to see if a culinary herb can help rebuild the gut microbiome.

Why Use Garlic?

Garlic has been shown to offer numerous benefits for the gut microbiome, contributing to overall health and disease prevention. None of the clinical studies are on dogs. All of them are for human health. Here are the key benefits:

Prebiotic Effects

Garlic contains prebiotic components such as fructans, which help in promoting the growth of beneficial gut bacteria. This prebiotic effect is crucial for maintaining a healthy gut microbiome and enhancing gut health (Keyu Chen et al., Fateme Ettehad-Marvasti et al.)

Modulation of Gut Microbiota

Garlic and its derivatives, such as allicin-free garlic and aged garlic, have been found to modulate the composition of the gut microbiota. They increase the abundance of beneficial bacteria like Bifidobacterium and Akkermansia, while reducing harmful bacteria such as Prevotella and Escherichia coli (Keyu Chen et al., Fateme Ettehad-Marvasti et al., Deping Han et al., Jina Ha et al.).

Anti-Inflammatory and Antioxidant Properties

Garlic-derived compounds, including polysaccharides and metabolites like propyl propane thiosulfinate, exhibit anti-inflammatory and antioxidant activities. These properties help in reducing intestinal inflammation and oxidative stress, which are beneficial for gut health (Xin Shao et al., Ling Zhu et al., Deping Han et al.).

Enhancement of Gut Immunity

Bioconverted garlic ferments have been shown to stimulate the intestinal immune system by increasing the production of immune-related factors such as interferon-gamma and tumor necrosis factor-alpha. This immune modulation supports a healthy gut environment (Genevieve Tonog et al.).

Protection Against Pathogens

Garlic-derived compounds can protect against enteric pathogens by modulating the gut microbiota and enhancing the host’s immune response. This protective effect is crucial for preventing infections and maintaining gut health (Ling Zhu et al.).

Improvement in Gut Health and Disease Prevention

Garlic supplementation has been associated with improvements in conditions like dyslipidemia, colitis, and atherosclerosis by modulating the gut microbiota and reducing harmful metabolites like trimethylamine-N-oxide (TMAO) (Keyu Chen et al., Xin Shao et al., Suraphan Panyod et al.).

A Small Amount Of Garlic is Safe For Dogs

In summary, garlic offers a range of benefits for the gut microbiome, including prebiotic effects, modulation of gut bacteria, anti-inflammatory and antioxidant properties, enhancement of gut immunity, protection against pathogens, and improvement in gut health and disease prevention. These benefits highlight garlic’s potential as a functional food for promoting gut health.

While these benefits are promising, we also want to know at what level is safe for dogs, and at what level would be toxic. The research indicates it requires very high levels of garlic before it can be toxic to dogs.

References

Büyükdeveci, M., Balcázar, J., Demirkale, I., & Dikel, S. (2018). Effects of garlic-supplemented diet on growth performance and intestinal microbiota of rainbow trout (Oncorhynchus mykiss). Aquaculture, 486, 170-174. https://doi.org/10.1016/J.AQUACULTURE.2017.12.022

Chen, K., Nakasone, Y., Xie, K., Sakao, K., & Hou, D. (2020). Modulation of Allicin-Free Garlic on Gut Microbiome. Molecules, 25. https://doi.org/10.3390/molecules25030682

Chen, K., Xie, K., Liu, Z., Nakasone, Y., Sakao, K., Hossain, A., & Hou, D. (2019). Preventive Effects and Mechanisms of Garlic on Dyslipidemia and Gut Microbiome Dysbiosis. Nutrients, 11. https://doi.org/10.3390/nu11061225

Ettehad-Marvasti, F., Ejtahed, H., Siadat, S., Soroush, A., Hoseini-Tavassol, Z., Hasani-Ranjbar, S., & Larijani, B. (2022). Effect of garlic extract on weight loss and gut microbiota composition in obese women: A double-blind randomized controlled trial. Frontiers in Nutrition, 9. https://doi.org/10.3389/fnut.2022.1007506

Ha, J., Kim, J., Kim, S., Lee, K., & Shin, H. (2024). Garlic-Induced Enhancement of Bifidobacterium: Enterotype-Specific Modulation of Gut Microbiota and Probiotic Populations. Microorganisms, 12. https://doi.org/10.3390/microorganisms12101971

Han, D., Guan, X., Zhu, F., Yang, Q., & Su, D. (2024). Oral aged garlic (Allium sativum) alleviates ulcerative colitis in mice by improving gut homeostasis. Food & function. https://doi.org/10.1039/d4fo03105a

Lee, K. W., Yamato, O., Tajima, M., Kuraoka, M., Omae, S., & Maede, Y. (2000). Hematologic changes associated with the appearance of eccentrocytes after intragastric administration of garlic extract to dogs. American Journal of Veterinary Research, 61(11), 1446-1450. https://doi.org/10.2460/ajvr.2000.61.1446

Panyod, S., Wu, W., Chen, P., Chong, K., Yang, Y., Chuang, H., Chen, C., Chen, R., Liu, P., Chung, C., Huang, H., Lin, A., Shen, T., Yang, K., Huang, T., Hsu, C., Ho, C., Kao, H., Orekhov, A., … Sheen, L. (2021). Atherosclerosis amelioration by allicin in raw garlic through gut microbiota and trimethylamine-N-oxide modulation. NPJ Biofilms and Microbiomes, 8. https://doi.org/10.21203/RS.3.RS-519786/V1

Shao, X., Sun, C., Tang, X., Zhang, X., Han, D., Liang, S., Qu, R., Hui, X., Shan, Y., Hu, L., Fang, H., Zhang, H., Wu, X., & Chen, C. (2020). Anti-Inflammatory and Intestinal Microbiota Modulation Properties of Jinxiang Garlic (Allium sativum L.) Polysaccharides toward Dextran Sodium Sulfate-Induced Colitis. Journal of Agricultural and Food Chemistry. https://doi.org/10.1021/acs.jafc.0c04773

Tonog, G., Yu, H., Moon, S., Lee, S., Jeong, H., Kim, H., Kim, K., Suh, H., & Kim, H. (2024). Garlic Bioconverted by Bacillus subtilis Stimulates the Intestinal Immune System and Modulates Gut Microbiota Composition. Molecular Nutrition & Food Research, e2400504. https://doi.org/10.1002/mnfr.202400504

Wen-hai, H. (2008). Long-term(12-week)Toxicity Test on Dogs with Selenium-enriched garlic.

Yamato, O., Tsuneyoshi, T., Ushijima, M., Jikihara, H., & Yabuki, A. (2018). Safety and efficacy of aged garlic extract in dogs: upregulation of the nuclear factor erythroid 2-related factor 2 (Nrf2) signaling pathway and Nrf2-regulated phase II antioxidant enzymes. BMC Veterinary Research, 14(1), 373. https://doi.org/10.1186/s12917-018-1699-2

Zhu, L., Andersen-Civil, A., Castro-Meija, J., Nielsen, D., Blanchard, A., Olsen, J., Thamsborg, S., & Williams, A. (2022). Garlic-Derived Metabolites Exert Antioxidant Activity, Modulate Gut Microbiota Composition and Limit Citrobacter rodentium Infection in Mice. Antioxidants, 11. https://doi.org/10.3390/antiox11102033

---