Garlic & The Microbiome 


Garlic is a quintessential spice used in many cultures. Growing up in my household, garlic was part of every dinner meal in some way–primarily, we sautéed the garlic with onions and added this to vegetable dishes. Historically, the use of garlic is often found in ancient medical texts spanning thousands of years back and across many continents. Garlic was reportedly used to improve athleticism during the initial Olympic games in Greece, and in 1858, Louis Pasteur demonstrated the antibacterial properties of garlic. To this day, the spice is a staple for cooking in most homes, and commercially, garlic is blended into sauces, soups, and seasoning blends. 

The pungent odiferous aroma and flavor of garlic comes from over 30 sulfur compounds. Garlic contains more sulfur compounds than any allium plant species, including onion. Due to the many ways in which it is processed, different garlic preparations will contain varying amounts of these sulfur related compounds. The espoused health benefits of garlic are typically associated with its sulfur-rich compounds. There are thousands of publications confirming the health benefits of garlic for a variety of conditions. 

General Health Benefits of Garlic 

Animal and human studies reveal a correlation between the consumption of garlic and subsequent reduction in the incidence of cancers. Garlic has been shown to activate antioxidant systems in the body and contribute to increased levels of our body's main antioxidant, glutathione. Garlic supplements are often used in cardiovascular cases to assist with lowering blood pressure—a robust amount of data demonstrates its benefit in heart health. Garlic also benefits liver disease, as it exhibits anti-inflammatory and antioxidant liver-protective properties in non-alcoholic fatty liver disease. 

Garlic in the Intestinal Microbiome 

The human microbiome contains trillions of microbes. Within this family of microbes are bacteria, fungi, viruses, and more. When the microbiome becomes imbalanced, with either overgrowth or undergrowth of specific microbes, we call this dysbiosis. Studies show that intestinal dysbiosis represents a major piece of the puzzle where chronic diseases are concerned. Dysbiosis is also a common factor in many gut diseases such as irritable bowel syndrome, small intestine bacterial overgrowth, ulcerative colitis, and Crohn’s disease. 

Garlic has multifactorial actions in the gut. For one, it supports healthy bacterial populations in the gut by behaving as a prebiotic. Prebiotics are food components that are able to bypass destruction or absorption in the stomach and small intestines, and subsequently reach the large intestines intact. Once in the large intestines, these specific food components are essentially eaten by the beneficial gut bacteria which, in turn, will produce more beneficial gut bacteria. Garlic exhibits prebiotic activity and increases the beneficial Lactobacillus acidophilus bacteria.

One of the earliest discovered benefits of garlic is its bacteria-fighting properties. Numerous studies reveal the antibacterial properties of garlic against a variety of bacteria. Garlic is often used to reduce bacteria in small intestine bacterial overgrowth (SIBO) where there is an overgrowth of bacteria leading to a variety of unpleasant gut symptoms. It has also been demonstrated that garlic has the ability to block H. pylori bacteria in the stomach, a bacteria that can cause ulcers of the stomach and small intestine. Along with its prebiotic and antibacterial properties, garlic also possesses antifungal properties. Numerous studies have shown that different garlic formulations have the ability to kill Candida albicans, a fungus that can become imbalanced within the human gut. 

Garlic in intestinal Disease 

There is limited research on garlic in specific bowel diseases. There are a few small cell and animal studies demonstrating benefit in gut health, however, the data is not very robust. In a model of experimental colon inflammation, the garlic component allicin was shown to exhibit therapeutic benefit. Garlic has also demonstrated benefit in inflammatory bowel disease beyond the gut effects, specifically in lowering inflammation in the body overall. Given the understanding of intestinal dysbiosis in gastrointestinal disorders, garlic would, theoretically, be a wonderful candidate for reducing harmful bacteria in the gut. 

A Word of Caution on Garlic 

Garlic is considered safe by the U.S. Food and Drug Administration, however, many people have sensitivities and allergies to garlic that should be taken seriously. In animal models, high amounts of garlic irritated the mucous lining of the gut. Other animal models have also demonstrated toxic effects of high garlic doses. Caution should be utilized in any person with a sensitivity to garlic. Also of note, a garlic allergy is not congruent to sulfa drug allergies. 

Use of garlic in supplement form or dietary form for a specific condition should be guided by a practitioner, especially when the condition relates to the gastrointestinal tract. Garlic can cause further gut upset in those with underlying intestinal issues. The low FODMAP diet is utilized as a tool for minimizing symptoms in those with a variety of gut issues. Garlic is included in the list of foods to avoid on the low FODMAP diet as it contains prebiotics that can be problematic for certain gut conditions. 


Garlic is a wonderful, potent spice that has many health benefits extending to the vast microbiome. Garlic appears to be a useful tool for specific gut conditions—but not for every gut condition. Working with a skilled practitioner can help you figure out if this spice should be supplemented or increased in your diet. Garlic is considered safe for human consumption and can be enjoyed as a flavor and spice agent.

Dr. Asia Muhammad, ND

Naturopathic Doctor

Dr. Muhammad, ND has committed her practice to honoring the power of lifestyle modification to achieve optimal health. She has a special interest in GI health, evidenced in her practice’s focus on gastroenterology, as well as mind-body medicine, and stress management. Dr. Muhammad provides her patients individualized attention and evidence-based naturopathic solutions, including food, movement, botanicals, supplementation, and hypnosis. When she’s not working, she likes to play the piano, dance, and explore new foods.

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