Garlic is the edible bulb from a plant in the lily family. It was traditionally used for health purposes by people in many parts of the world, including the Egyptians, Greeks, Romans, Chinese, Japanese, and Native Americans.

Currently, garlic is used as a dietary supplement for many purposes, including for weight loss, high blood cholesterol, high blood pressure, and the common cold, as well as in attempts to prevent cancer and other diseases.

Fresh garlic, garlic powder, and garlic oil are used to flavor foods. Garlic dietary supplements are sold as tablets or capsules. Garlic oil may be used topically (applied to the skin).

A great deal of research has been done on garlic, but much of it consists of small, preliminary, or low-quality studies. (Source 1).

Uses of Garlic in Weight Loss

The maker of a dietary supplement claims are not subject to FDA review or approval before marketing. Also, the type or quality of research used to support claims can vary. When a dietary supplement is marketed as “clinically proven” to cause weight loss, there should be some type of clinical evidence to support it. Such a claim, however, provides no details about the clinical research and the supplement usually included multiple ingredients (for example raspberry ketone, caffeine, bitter orange, ginger root extract, garlic root extract, as well as other herbs, vitamins and minerals), making it impossible to judge which ingredients caused a treatment effect.

In a small trial involving 70 obese adults, where some participants were given the multiple ingredient weight loss supplements and others placebo (dummy pills) over a period of eight weeks. Plus all of the participants were placed on a restricted diet and exercise program. Forty-five people completed all eight weeks of the trial. Among people completing the trial, the average weight loss in the supplement group was 4.2 pounds (1.9 kilograms). The average weight loss in the placebo group was 0.9 pounds (0.4 kilograms). Due to the poorly designed trial with the small size, method and duration of the trial. Based on the insufficient evidence, it’s impossible draw conclusions about the potential benefits garlic in weight loss. (Source 2).

Uses of Garlic and Honey for Weight Loss

For garlic and weight as above, insufficient evidence to draw the conclusions.

As for honey, it’s a thick, sweet, syrupy substance that bees make as food from the nectar of flowers and store in honeycombs. (Source 3). Apart from honey being used as a sweetener, with potential wound repair and antibacterial activities. There is currently no evidence that combining garlic and honey can lead to weight loss.

Garlic and Cancer Prevention

  • Protective effects from garlic may arise from its antibacterial properties 4 or from its ability to block the formation of cancer-causing substances 5, halt the activation of cancer-causing substances 6, enhance DNA repair 7, reduce cell proliferation, or induce cell death 8.
  • Study limitations 9, 10, 11, 12, including the accuracy of reporting the amounts and frequency of garlic consumed, and the inability to compare data from studies that used different garlic products and amounts make an overall conclusion about garlic and cancer prevention extremely difficult. Since many of the studies looking at garlic use and cancer prevention have used multi-ingredient products, it is unclear whether garlic alone or in combination with other nutritional components may have the greatest effect. (Source 13).Well-designed dietary studies in humans using predetermined amounts of garlic (intervention studies) are needed to determine potentially effective intakes. Studies directly comparing various garlic preparations are also needed.
  • Conclusion: The National Cancer Institute, part of the National Institutes of Health, does not recommend any dietary supplement for the prevention of cancer, but recognizes garlic as one of several vegetables with potential anticancer properties. Because all garlic preparations are not the same, it is difficult to determine the exact amount of garlic that may be needed to reduce cancer risk. Furthermore, the active compounds present in garlic may lose their effectiveness with time, handling, and processing. The World Health Organization’s (WHO) guidelines for general health promotion for adults is a daily dose of 2 to 5 g of fresh garlic (approximately one clove), 0.4 to 1.2 g of dried garlic powder, 2 to 5 mg of garlic oil, 300 to 1,000 mg of garlic extract, or other formulations that are equal to 2 to 5 mg of allicin. (Source 13).

What Have We Know About Garlic

  • Cholesterol: A study from Stanford University casts doubt on the effectiveness of garlic to lower LDL (low density lipoprotein) “bad” cholesterol levels in adults with moderately high cholesterol. Christopher Gardner, Ph.D., and colleagues conducted a randomized, placebo-controlled trial 14 studying whether three different formulations of garlic could lower LDL cholesterol. The study participants were randomly divided into four groups to receive raw garlic, a powdered garlic supplement, an aged extract supplement, or a placebo.The 169 participants who completed the study had their cholesterol levels checked monthly for the duration of the 6-month trial.
  • Conclusion: None of the formulations of garlic had a statistically significant effect on the LDL cholesterol levels (the so-called “bad” cholesterol that’s linked to increased heart disease risk).
  • Hypertension: Garlic is widely used by patients for its blood pressure lowering effects. In a recent review (source 15) of the currently available evidence to determine the impact of garlic on cardiovascular events and mortality in patients with hypertension. Based on data from two randomized controlled trials that compared garlic to placebo in patients with hypertension, there is insufficient evidence to determine if garlic provides a therapeutic advantage versus placebo in terms of reducing the risk of mortality and cardiovascular morbidity in patients diagnosed with hypertension. Verdict: Save your money.
  • Pre-eclampsia: Pre-eclampsia is a serious complication of pregnancy occurring in about 2% to 8% of women. It is identified by increased blood pressure and protein in the urine, but women often suffer no symptoms initially. It can, through constriction of the blood vessels in the placenta, interfere with food and oxygen passing to the baby, thus inhibiting the baby’s growth and causing the baby to be born too soon. Women can be affected through problems in their kidneys, liver, brain, and clotting system. Conclusions — there is insufficient evidence to recommend increased garlic intake for preventing pre-eclampsia and its complications. (source 16). Further large randomised trials evaluating the effects of garlic are needed before any recommendations can be made to guide clinical practice.
  • Peripheral arterial occlusive disease affecting the legs: The most common symptom of peripheral arterial occlusive disease is intermittent claudication, discomfort in the legs that is triggered by exercise and relieved with rest. The underlying cause is atherosclerosis. Risk factors associated with the development of peripheral arterial disease include cigarette smoking, raised blood cholesterol and other fats (lipids), high blood pressure and diabetes. Review authors 17 made a thorough search of the medical literature and found one controlled trial in which 78 participants with peripheral arterial occlusive disease were randomised to receive garlic or a placebo medication. The dose of garlic was two coated tablets of 200 mg oral standardised garlic powder twice daily. Both men and women, aged 40 to 75 years, were included although sixteen did not keep to their treatment. Conclusion: there was no statistically significant effect of garlic on pain-free walking distance between those taking garlic and those on placebo (dummy pills).
  • Common Cold: Garlic is popularly believed to be useful for the common cold. This belief is based on traditional use and some laboratory evidence that garlic has antibacterial and antiviral properties. On average, adults have two to four common colds per year. There is insufficient clinical trial evidence regarding the effects of garlic in preventing or treating the common cold. (Source 18).

What Do We Know About Safety ?

  • Garlic is probably safe for most people in the amounts usually eaten in foods.
  • Side effects include breath and body odor, heartburn, and upset stomach. These side effects can be more noticeable with raw garlic.
  • Some people have allergic reactions to garlic.
  • Taking garlic may increase the risk of bleeding. If you take an anticoagulant (blood thinner) such as warfarin (Coumadin) or if you need surgery, tell your health care provider if you’re taking or planning to take garlic dietary supplements.
  • Garlic has been found to interfere with the effectiveness of some drugs, including saquinavir, a drug used to treat HIV infection.
  • Garlic bulbs are sometimes contaminated with the bacterium Clostridium botulinum. C. botulinum can grow and produce botulinum toxin in garlic-in-oil products that are not refrigerated and do not contain antibacterial agents.

Conclusion 19

A recent increase in the popularity of alternative medicine and natural products has renewed interest in garlic and their derivatives as potential natural remedies. Although it is shown that garlic may have a significant clinical potential either in their own right or as adjuvant therapy in different disorders, however more standard experiments and researches are needed to confirm the beneficial effect of garlic in various diseases (source 20. Future trials on the effect of garlic should include information on the dosage of active ingredients of standardized garlic preparations for better comparison of trials.

Although garlic is believed to be a safe substance, long-term trials of reasonable duration would provide insights into the possible side-effects of different garlic extracts. The safety of garlic should be tested especially in pregnant or breastfeeding women as well as in young children 21; 22. Long-term and large trials are also needed to evaluate the differences in mortality, serious adverse events, and morbidity of cancer and cardiovascular diseases after garlic therapy.

  1. National Center for Complementary and Integrative Health – Garlic –[]
  2. Mayo Foundation for Medical Education and Research – Over-the-counter weight-loss pills –[]
  3. U.S. Food and Drug Administration (FDA) – Draft Guidance for Industry: Proper Labeling of Honey and Honey Products –[]
  4. Ruddock PS, Liao M, Foster BC, et al. Garlic natural health products exhibit variable constituent levels and antimicrobial activity against Neisseria gonorrhoeae, Staphylococcus aureus and Enterococcus faecalis. Phytotherapy Research 2005; 19(4):327–334.[]
  5. Shenoy NR, Choughuley AS. Inhibitory effect of diet related sulphydryl compounds on the formation of carcinogenic nitrosamines. Cancer Letters 1992; 65(3):227–232.[]
  6. Milner JA. Mechanisms by which garlic and allyl sulfur compounds suppress carcinogen bioactivation. Garlic and carcinogenesis. Advances in Experimental Medicine and Biology 2001; 492:69–81.[]
  7. L’vova GN, Zasukhina GD. Modification of repair DNA synthesis in mutagen-treated human fibroblasts during adaptive response and the antimutagenic effect of garlic extract. Genetika 2002; 38(3):306–309.[]
  8. Hsing AW, Chokkalingam AP, Gao YT, et al. Allium vegetables and risk of prostate cancer: A population-based study. Journal of the National Cancer Institute 2002; 94(21):1648–1651.[]
  9. Li H, Li HQ, Wang Y, et al. An intervention study to prevent gastric cancer by micro-selenium and large dose of allitridum. Chinese Medical Journal (English) 2004; 117(8):1155–1160.[]
  10. You WC, Brown LM, Zhang L, et al. Randomized double-blind factorial trial of three treatments to reduce the prevalence of precancerous gastric lesions. Journal of the National Cancer Institute 2006; 98(14):974–983.[]
  11. Tanaka S, Haruma K, Kunihiro M, et al. Effects of aged garlic extract (AGE) on colorectal adenomas: A double-blinded study. Hiroshima Journal of Medical Sciences 2004; 53(3–4):39–45.[]
  12. Tilli CM, Stavast-Kooy AJ, Vuerstaek JD, et al. The garlic-derived organosulfur component ajoene decreases basal cell carcinoma tumor size by inducing apoptosis. Archives of Dermatological Research 2003; 295(3):117–123.[]
  13. National Cancer Institute – Garlic and Cancer Prevention –[][]
  14. Gardner CD, Lawson LD, Block E, et al. Effect of raw garlic vs. commercial garlic supplements on plasma lipid concentrations in adults with moderate hypercholesterolemia: a randomized clinical trial. Archives of Internal Medicine. 2007
    ;167(4):346–353. []
  15. Cochrane Review 15 August 2012 – Garlic for Hypertension –[]
  16. Cochrane Review – Garlic for preventing pre-eclampsia and its complications –[]
  17. Cochrane Review 30 April 2013 – Garlic for peripheral arterial occlusive disease affecting the legs –[]
  18. Cochrane Review 11 November 2014 – Garlic for the common cold –[]
  19. National Center for Biotechnology Information, U.S. National Library of Medicine – Garlic: a review of potential therapeutic effects –[]
  20. Avicenna J Phytomed. 2014 Jan-Feb; 4(1): 1–14 – Garlic: a review of potential therapeutic effects –[]
  21. Budzynska K, Gardner ZE, Dugoua JJ, Low Dog T, Gardiner P. Systematic review of breastfeeding and herbs. Breastfeed Med. 2012;7:489–503.[]
  22. Dante G, Pedrielli G, Annessi E, Facchinetti F. Herb remedies during pregnancy: a systematic review of controlled clinical trials. J Matern Fetal Neonatal Med. 2013;26:306–312.[]
Health Jade Team

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