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Superfood Spotlight: Garlic

Garlic has been a staple in the human diet and in medicine for thousands of years.1-3 Some might even call it the food of legends, one of that supposedly protects against everything from common colds to heart disease.1-4 Garlic was traditionally used for health purposes by people all over the world, including the Egyptians, Greeks, Romans, Chinese, and Japanese. During the Middle Ages, garlic was reputed to have been highly effective against the plague.5 While many of the traditional medicinal uses of herbs and plants have yet to be supported by vigorous randomized, controlled studies, the nutritional and medicinal value of garlic has stood the test of time. Even today, garlic is commonly promoted as a dietary supplement for certain health conditions.1

Garlic is versatile. In fact, its three in one! Garlic is a vegetable because it is an edible plant. It’s also an herb, which is defined as any plant used as medicine, seasoning, or flavoring.1 Finally, it’s a spice, which is a dried plant-derived substance used to flavor food.4 On top of being a relatively nutrient-dense food, garlic contains biologically active components that contribute to its pharmacological properties. One of its sulfur-based compounds, allicin, gives garlic its savory flavor and pungent smell. Allicin is also what makes garlic a healthy addition to your diet. Here are some reasons this herb ranks highly as a health-protecting food.

Strong Antioxidant Capacity for Metabolic Health

Many of garlic’s health benefits, especially as they relate to heart health, are grounded in its antioxidant properties.4-6 Antioxidants fight free radicals—unstable molecules your body naturally forms when it converts food into energy—that cause oxidative stress, which can damage cells.7 Oxidative stress plays a role in a variety of diseases, increases inflammation in the body, and can accelerate age-related processes.8 

Garlic consumption in particular has been shown to mitigate multiple risk factors associated with heart diseases. For example, the antioxidant properties of aged garlic extract has been shown to reduce inflammation, particularly in the vessels of the heart. This may help prevent atherosclerosis—a condition caused when there is a build-up of fats, cholesterol, and other substances in and on the artery walls .8-10 Similarly, garlic has also been shown to help lower cholesterol, blood pressure, and blood sugar.1,4,10 However, these changes are typically observed when people consume high supplemental doses of garlic, particularly in powder or tablet forms, so you may not gain the same health benefits by adding a couple of cloves to a recipe.4 It may take more than eight weeks before noting any improvement.1 Research about this herb’s effect on metabolic and heart disease can also be inconsistent. Experts say this may be due to the large variation in garlic products—including powders, as a fresh or raw plant, oils, and more—which make it difficult to determine the true effect of garlic on cardiovascular morbidity and mortality.6

Antimicrobial Properties 

Garlic extract has been shown to have antibacterial and antifungal properties.11 This herb has been used throughout history to treat various diseases and wounds before antibiotics were widely available. Now that antibiotic-resistance against microorganisms has become such a serious issue, some researchers are again turning toward garlic’s antimicrobial activities because of its inhibitory effects against pathogenic viruses, bacteria, and fungi.12-15 

While garlic is not as potent as modern antibiotics, it may help the body resist or destroy viruses and other microorganisms, such as staph, E. coli, and Salmonella.5 A 2020 study showed that garlic extracts could be therapeutic in treating bacterial-mediated urinary tract infections.16 Components of garlic have also been shown to have to inhibit viral cell growth in warts. In one placebo-controlled trial, the topical application of garlic chloroform extract—a type of liquid extraction—resulted in the complete resolution of cutaneous warts with no recurrence after three to four months.17,18 Finally, garlic may help treat athlete’s foot, a type of recurring fungal infection characterized by a scaly, itching, and stinging rash.19 A small, randomized, controlled trial showed that topical application of ajoene—a derivative of garlic—resulted in complete cure in 79 percent of participants after seven days.20 Always consult a physician before therapeutic garlic consumption. Its health benefits can take weeks to show any significant effect and topical application of garlic exacts can cause itching, redness, and swelling in some people.

Prevents Inflammation

Garlic has potent anti-inflammatory properties, making it an important tool for preventing inflammatory processes that characterizes many chronic and acute condtions.7,11,15,21 When the body encounters an offending agent, such as viruses, bacteria, or toxic chemicals, it activates your immune system.22 Once those alarms bells go off, your body sends out inflammatory cells and cytokines—substances that stimulate more inflammatory cells—to combat the offending agents. While inflammation is a natural biological response, chronic inflammation, which occurs when your body continues dispatching these cells even when there is no danger, can damage healthy tissues and organs.23 Garlic has been shown to exert potent anti-inflammatory effects by decreasing the inflammatory biomarkers, including those found in people with renal disease and certain cancers.2,14,24 Garlic supplementation can also boost microbial richness and diversity, which can counteract inflammation from obesity, hypertension, diabetes, and inflammatory bowel disease.25 Garlic oil has been used to treat sore and inflamed joints or muscles; the Arthritis Foundation even recommends it to help prevent cartilage damage from arthritis.26

Potential Risks

While garlic is safe and well tolerated in most peoples’ diets, there is a small risk that eating large quantities of it (i.e., more than four cloves a day) can affect the blood’s ability to clot.1,15,18 Given this, people should be wary of consuming garlic before and after surgery and not to exceed this amount if taking anticoagulant medications.1 Similarly, garlic may interfere with the effectiveness of some drugs. Other side effects include breath and body odor, heartburn, and upset stomach.

Preparation

The pharmacologic properties of garlic depend on the way it is prepared, so taking advantage of its health benefits can become complicated. While garlic is usually cooked and added for extra flavor, it can also be eaten raw.1,15,16 Raw garlic may better retain allicin, which is responsible for many of its health benefits. Some studies show that roasting, boiling, heating, or pickling garlic can significantly reduce its allicin content.27,28 

Garlic supplements are also very popular. These can come in the forms of powders, oils, extracts tablets, capsules, or topical preparations.2,15 Research shows that aged garlic extract (AGE), which undergoes a 20-month ageing and extracting process, is richer in antioxidants than fresh garlic or other preparations.6,15 This means that AGE may be an optimal choice for those looking to maximize the nutritional benefits of garlic. It is worth noting that not all garlic supplements are standardized, and even standardized brands’ bioavailability of allicin and other important nutrients will vary.2,11

Bottom Line

Garlic has been used for medicinal and nutritional purposes for thousands of years, and a recent increase in the popularity of alternative medicine and natural products has renewed interest this in herb and its derivatives as potential natural remedies.2 Garlic’s culinary versatility is closely matched by its various health benefits, including its high antioxidant capacity, antimicrobial assets, and anti-inflammatory properties. More research is needed to further define and confirm this herb’s health benefits, but current studies have demonstrated some therapeutic potential.2 Still, you should always contact your doctor before consuming garlic or its related products for health purposes.


Editor’s note

Consult with your physician, dietitian/nutritionist, or other qualified healthcare professional to determine what the best nutrition plan is for you.

 


Sources

1. Weil A. Garlic. National Geographic Guide to Medicinal Herbs: The World’s Most Effective Healing Plants. Washington, DC: National Geographic Partners;2010:152-157.

2. Bayan L, Koulivand PH, Gorji A. Garlic: a review of potential therapeutic effects. Avicenna J Phytomed. 2014;4(1):1-14.

3. NCCIH. Updated Dec 2020. Garlic. National Center for Complementary and Integrative Health website. https://www.nccih.nih.gov/health/garlic. Accessed 28 Mar 2022.

4. Merschel M. 19 Apr 2021. Sorting folklore from fact on the health benefits of garlic. American Heart Association website. https://www.heart.org/en/news/2021/04/19/sorting-folklore-from-fact-on-the-health-benefits-of-garlic. Accessed 1 Apr 2022.

5. Longe LL. Garlic. The Gale Encyclopedia of Alternative Medicine, 5th Edition. Farmington Hills, MI: Gale; 2020: 1097-1102.

6. Martini N. Garlic. J Prim Health Care. 2014;6(4):337–338.

7. NCCIH. Updated Nov 2013. Antioxidants: in depth. National Center for Complementary and Integrative Health website. https://www.nccih.nih.gov/health/antioxidants-in-depth. Accessed 1 Apr 2022.

8. Tesfaye A. Revealing the therapeutic uses of garlic (Allium sativum) and its potential for drug discovery. Sci World J. 2021;2021:8817288. 

9. Tsuneyoshi T. BACH1 mediates the antioxidant properties of aged garlic extract. Exp Ther Med. 2020:1500–1503

10. NIH. Updated 24 Mar 2022. What is atherosclerosis? NIH: National Heart, Lung, and Blood Institute website. https://www.nhlbi.nih.gov/health/atherosclerosis. Accessed 4 Apr 2022.

11. Ried K. Updated Dec 2016. Garlic. Linus Pauling Institute Micronutrient Information Center website. https://lpi.oregonstate.edu/mic/food-beverages/garlic. Accessed 29 Mar 2022.

12. Gökalp F. The inhibition effect of garlic-derived compounds on human immunodeficiency virus type 1 and saquinavir. J Biochem Mol Toxicol. 2018;32:e22215.

13. Serrano HDA, Mariezcurrena-Berasain MA, Del Carmen Gutiérrez Castillo A, et al. Antimicrobial resistance of three common molecularly identified pathogenic bacteria to Allium aqueous extracts. Microb Pathog. 2020;142:104028.

14. Said MM, Watson C, Grando D. Garlic alters the expression of putative virulence factor genes SIR2 and ECE1 in vulvovaginal C. albicans isolates. Sci Rep. 2020;10(1):3615. 

15. Ansary J, Forbes-Hernández TY, Gil E, et al. Potential health benefit of garlic based on human intervention studies: a brief overview. Antioxidants (Basel). 2020;9(7):619. 

16. Lionel OO, Adegboyega IP, Adeleke EO, Olufunke BC. Antimicrobial activity of garlic (Allium sativum ) on selected uropathogens from cases of urinary tract infection. Ann Trop Pathol. 2020;11(2);133.

17. Dehghani F, Merat A, Panjehshahin MR, Handjani F. Healing effect of garlic extract on warts and corns. Int J Dermatol. 2005;44:612–615.

18. Pazyar N, Feily A. Garlic in dermatology. Dermatol Reports. 2011;3(1):e4. 

19. Mayo Clinic Staff. Updated 15 Oct 2021. Athlete’s foot. Mayo Clinic website. https://www.mayoclinic.org/diseases-conditions/athletes-foot/symptoms-causes/syc-20353841. Accessed 4 Apr 2022.

20. Ledezma E, DeSousa L, Jorquera A, et al. Efficacy of ajoene, an organosulphur derived from garlic, in the short-term therapy of tinea pedis. Mycoses. 1996;39(9-10):393-395.

21. Lee DY, Li H, Lim HJ, et l. Anti-inflammatory activity of sulfur-containing compounds from garlic. J Med Food. 2012;15(11):992-999.

22. Cleveland Clinic Staff. Updated 28 Jul 2021. Inflammation. Cleveland Clinic website. https://my.clevelandclinic.org/health/symptoms/21660-inflammation#:~:text=What%20is%20inflammation%3F,that%20stimulate%20more%20inflammatory%20cells). Accessed 4 Apr 2022.

23. 12 Apr 2021. Playing with the fire of inflammation. Harvard Health website. https://www.health.harvard.edu/staying-healthy/playing-with-the-fire-of-inflammation. Accessed 4 Apr 2022.

24. Schäfer G, Kaschula CH. The immunomodulation and anti-inflammatory effects of garlic organosulfur compounds in cancer chemoprevention. Anticancer Agents Med Chem. 2014;14(2):233-240. 

25. Ried K, Travica N, Sali A. The effect of kyolic aged garlic extract on gut microbiota, inflammation, and cardiovascular markers in hypertensives: the GarGIC trial. Front Nutr. 2018;5:122. 

26. Best spices for arthritis. Arthritis Foundation website. https://www.arthritis.org/health-wellness/healthy-living/nutrition/healthy-eating/best-spices-for-arthritis. Accessed 4 Apr 2022.

27. Lawson LD, Hunsaker SM. Allicin bioavailability and bioequivalence from garlic supplements and garlic foods. Nutrients. 2018;10(7):812.

28. Shin JH, Ryu JH, Kang MJ, et al Short-term heating reduces the anti-inflammatory effects of fresh raw garlic extracts on the LPS-induced production of NO and pro-inflammatory cytokines by downregulating allicin activity in RAW 264.7 macrophages. Food Chem Toxicol. 2013;58:545-551.   

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