What are the health benefits of garlic? A summary of evidence from allicin, antibacterial properties, and cardiovascular benefits.

Garlic is a staple in almost every family kitchen, and its unique pungent aroma can add flavor to many dishes.However, whenever garlic is mentioned, it is always accompanied by all sorts of health claims—antibacterial, anti-cancer, cold prevention, it sounds like it can do almost anything.So, what are the actual health benefits of regularly consuming garlic? And how many of these long-held health claims are actually valid?

This article will first clarify the components of garlic, then examine the strength of evidence for its antibacterial, anticancer, blood pressure, and blood lipid effects, and supplement a point that was less mentioned in the original manuscript:Allicin and alliin are actually two different substances.This article covers proper handling and cooking methods, the origin of garlic flavor, and who should pay special attention. All nutrient content figures are presented in [the format of the article].U.S. Department of Agriculture FoodData CentralThe amount is based on the edible portion per 100 grams.

I. Nutritional components of garlic: sulfides, alliin, and allicin

While garlic has a strong flavor, it's surprisingly nutritious. Raw garlic provides carbohydrates, protein, and dietary fiber, as well as minerals like potassium, calcium, manganese, and selenium, and vitamins C and B6. However, what truly makes garlic stand out isn't these basic nutrients, but rather...Its organic sulfur compounds—Allicin, diallyl disulfide (DADS), diallyl trisulfide (DATS), ajoene, and vinyldithiins all belong to this category.

The original text stated that "garlic contains more than 30 kinds of sulfides, which account for approximately 0.41 TP4T of the total weight of garlic." This figure should be stated more precisely:The commonly cited "approximately 0.41 TP4T" refers to the percentage of allicin by weight of a fresh garlic clove.The most abundant sulfide in garlic cloves is actually its precursor, allicin, which accounts for approximately 0.241 TP4T of fresh weight (the percentage can vary from 0.091 TP4T to 1.151 TP4T depending on the variety). Assuming each clove of raw garlic weighs about 3 grams, a single clove can produce only about 4 to 5 milligrams of allicin.

1. Allicin and alliin are two different substances.

The original manuscript mistakenly referred to "allicin" and "alliin" as two names for the same thing, which is a fairly common mislabeling, but the two are actually different:

• AlliinAllicin is a tasteless, stable sulfur-containing amino acid that naturally exists in whole garlic cloves.Precursor。
• AllicinThe product formed when alliin comes into contact with alliinase.This is the main source of garlic's pungent aroma and antibacterial activity.It is unstable and will rapidly decompose into various secondary metabolites.

In other words, allicin is the "raw material" and allicin is the "finished product." Their roles and activities are different and should not be confused.

2. Why "chop and let it sit" before cooking?

In a whole garlic clove, alliin and alliinase are stored in different locations and do not come into contact with each other, soA whole clove of garlic itself does not contain allicin.Only when garlic cloves are cut, crushed, or ground into a paste will the two meet and react chemically to produce allicin.

This also explains a common and practical suggestion:After chopping or crushing the garlic, let it air dry for about ten minutes before cooking.Allowing the reaction to proceed fully ensures that even after heating, some of the allicin already formed will be retained. Conversely, if a whole clove of garlic is added directly to the pan, the reaction will not have a chance to occur. However, it's important to note that...Heating for a short time will weaken some of the activity of raw garlic.—Studies have found that short-term heating reduces the anti-inflammatory effects of fresh raw garlic extract (see...).This studyTo get the vitality of raw garlic, you have to accept its spiciness; to get a milder flavor, you have to accept a reduction in active ingredients. It's difficult to have both.

3. The difference between "per 100 grams" and "one clove of garlic"

While the numbers in nutrition databases may look impressive, actual intake is key. Garlic is a seasoning ingredient, and the amount consumed at one time is usually small, so the difference after conversion is quite significant:

Table 1: Nutrient content of raw garlic (USDA FoodData Central; estimated at approximately 3 grams per clove)

Nutrients	per 100 grams of raw garlic	Each petal weighs approximately 3 grams.
calorific value	Approximately 149 kcal	Approximately 4.5 kcal
Moisture	Approximately 58.6 grams	Approximately 1.8 grams
protein	Approximately 6.4 grams	Approximately 0.2 grams
carbohydrate	Approximately 33.1 grams	Approximately 1.0 gram
Dietary fiber	Approximately 2.1 grams	Approximately 0.06 grams
鉀	Approximately 401 mg	Approximately 12 mg
鈣	Approximately 181 mg	Approximately 5 mg
Vitamin C	Approximately 31.2 mg	Approximately 0.9 mg
Vitamin B6	Approximately 1.24 mg	Approximately 0.04 mg
錳	Approximately 1.67 mg	Approximately 0.05 mg
硒	Approximately 14.2 micrograms	Approximately 0.4 micrograms

In other words, it's not practical to consider garlic as a "major source of minerals and vitamins"; its role is...Extremely low calories for intense flavorIncidentally, it also brought with it a small amount of trace elements and sulfur-containing compounds.

II. Garlic and its antibacterial properties: Strong laboratory evidence, limited human evidence.

Garlic has long been known as a "natural antibiotic," and this claim has its basis, but the level of evidence needs to be clarified.

In the laboratory, allicin and other organosulfur compounds have indeed exhibited a wide range of antibacterial activities, showing bacteriostatic, bactericidal, biofilm-inhibiting, and antitoxin-like effects against various bacteria (including some drug-resistant strains). The current understanding of the mechanism is as follows:These reactive sulfides bind to free sulfhydryl groups (-SH) on bacterial enzymes, forming disulfide bonds or undergoing S-allylmercapto modification, thus inactivating the enzymes and disrupting the integrity of the bacterial cell membrane.(SeeFrontiers in Microbiology Review及Journal of Biological Chemistry Research）。

1. Why is there a discrepancy between the claim that "eating garlic kills bacteria" and laboratory results?

Laboratory studies use purified or high-concentration garlic extracts, which act directly on bacteria in petri dishes; however, the situation is completely different when eating garlic daily.

• Dosage DifferenceA single clove of garlic can produce only a few milligrams of allicin, which is distributed across multiple dishes.
• Allicin is unstableIt decomposes rapidly at room temperature and may not be able to reach the target location in its original form.
• The internal environment is complexAfter entering the digestive tract, it will be further diluted and metabolized.

Therefore, it is reasonable to use garlic as a daily ingredient, butIt is not advisable to expect garlic to have a significant "antibacterial" effect.It should not be regarded as a substitute for antibacterial drugs.

2. Garlic cannot replace antibiotics.

If you haveHelicobacter pyloriFor infections or other illnesses requiring antibiotic treatment, it is essential to complete the course of treatment as directed by your doctor. To learn about the actual roles of garlic, honey, and probiotics in the treatment of Helicobacter pylori, please refer to the information on this website.Probiotics, honey, garlic and Helicobacter pylori〉。

III. Garlic and Cancer Risk: What Do Observational Studies and Randomized Trials Say?

The claim that "eating garlic fights cancer" is one of the most widespread beliefs, primarily stemming from observational studies comparing cancer rates between groups that "eat more garlic" and those that "eat less garlic." The limitation of these studies is that people who eat more garlic often also have healthier diets and lifestyles, making it difficult to attribute the benefits solely to garlic.

The actual images in the documents are also more complex than imagined:

• A systematic review and meta-analysis of 22 studies on Allium vegetables and garlic supplements,No significant association was found between higher intake and a decrease in overall cancer risk.(SeeThis integrated analysis）。
• Another meta-analysis of colorectal cancer showed that the group with the highest garlic intake had a lower risk (combined relative risk of approximately 0.80). However, it should be noted that...This effect is primarily derived from case-control studies; no similar results have been observed in generational studies alone.(SeeThis integrated analysisTherefore, a conservative approach should be taken when interpreting this.
• An analysis based on the U.S. Food and Drug Administration's (FDA) health claim evaluation system indicates that:There is no credible evidence to support a link between garlic consumption and a reduced risk of stomach, breast, lung, or endometrial cancer.For colon, prostate, esophageal, laryngeal, oral, ovarian, and renal cell carcinomas, there is only "very limited" evidence (see [link to relevant documentation]).This analysis）。

As for the randomized controlled trials with the highest level of evidence, the results are quite noteworthy. A study conducted in Linqi, Shandong, a high-incidence area of gastric cancer in China, involving 3,365 participants, had them continuously supplement with garlic extract and garlic oil for 7.3 years, with a follow-up period of over 22 years. The results showed:

• gastric cancer incidenceThe garlic group did not show statistically significant differences (win odds ratio 0.81, 95% confidence interval 0.57 to 1.13).
• Stomach cancer mortality rateGarlic groupSignificant decline(Hazard ratio 0.66, 95% confidence interval 0.43 to 1.00), and the utility belongs to the "later-onset" category (see...).BMJ 2019）。

By the way,World Cancer Research Fund (WCRF)Cancer prevention recommendations list garlic alongside onions and leeks as "non-starchy vegetables," advocating for a holistic diet rich in fruits and vegetables.No specific dosage or efficacy recommendations were given for garlic.This also reflects that the evidence for a single ingredient has not yet reached the level required to establish guidelines.

IV. Positive Evidence Worth Noting: Blood Pressure, Blood Lipids, and Immunity

The original draft focused on "clarifying exaggerated claims," but garlic actually has [some issues] in some areas.Verifiable and positive human researchThese are also things worth knowing.

1. Blood pressure

This is one of the more compelling pieces of evidence regarding garlic supplements. A meta-analysis of 20 randomized controlled trials involving 970 participants showed that, compared to placebo, garlic resulted in an average decrease of approximately 5.1 mmHg in systolic blood pressure and approximately 2.5 mmHg in diastolic blood pressure.Among participants with pre-existing high blood pressure (systolic/diastolic blood pressure ≥140/90 mmHg), the reduction was even greater—systolic blood pressure approximately 8.7 mmHg and diastolic blood pressure approximately 6.1 mmHg.(SeeJournal of Nutrition Integrated AnalysisAnother meta-analysis including seven randomized controlled trials also yielded consistent results (systolic blood pressure approximately -6.7 mmHg, diastolic blood pressure approximately -4.8 mmHg), and no serious adverse events were reported (see [link to analysis]).Phytomedicine integrated analysis）。

The National Center for Compassionate and Integrative Health (NCCIH)The summary is rather cautious:Limited evidenceGarlic supplements may lower blood pressure in people with high blood pressure.Slight declineIn other words, it can be considered a supplementary dietary adjustment, but the extent is limited.It cannot replace antihypertensive medication, nor should you stop taking it on your own.。

2. Blood lipids

NCCIH states: Garlic supplementsThis may cause a slight decrease in total cholesterol and low-density lipoprotein (LDL) in people who already have high cholesterol.Related meta-analyses also showed that for individuals with mildly elevated cholesterol, continued use for more than two months could reduce total cholesterol and LDL by about 10% (see...).The above review及Medicine Integrated AnalysisSimilarly, this is a "minor, supplementary" level and does not constitute a treatment for high cholesterol.

3. Immunity and Upper Respiratory Tract Infections

The original manuscript begins by mentioning "cold prevention," which needs to be treated equally. Currently, the only widely cited human study is a double-blind, randomized study of 146 participants over 12 weeks: participants took a supplement containing 180 mg of allicin daily, and the results showed significantly fewer colds (24 vs. 65) and shorter duration of illness (see...).This study）。

However, Cochrane's systematic review points out that among the studies searched,Only this one meets the inclusion criteria.Therefore, the existing evidence is still insufficient to support or refute the efficacy of garlic against the common cold (see...).Cochrane RetrospectiveThe NCCIH also pointed out that there is very little research in this area, with a 2022 review identifying only two small studies, both of which had methodological weaknesses.

A reasonable positioning is:This is an interesting but not yet established clue.Eating garlic in moderation in your daily diet is fine, but it should not replace proven protective measures such as vaccines and hand hygiene.

5. Why do I smell like garlic after eating garlic?

The original text mentioned that garlic can easily lead to "social embarrassment," which has a fairly clear scientific explanation and is more comprehensive than the original text describes.

Allicin decomposes to produce sulfur-containing metabolites such as diallyl disulfide (DADS) and methyl allyl sulfide (AMS).Methyl allyl sulfide can be excreted through respiration and skin.Therefore, even after brushing your teeth and rinsing your mouth, you may still smell the odor.A study published in Scientific ReportsInstrumental measurement of sulfur-containing compounds emitted from the skin surface revealed that after consuming roasted garlic, the skin's AMS emissions were significantly reduced.It will reach its peak in about 30 minutes.The levels then gradually decrease; the study also points out that AMS is relatively "latent" within skin tissue. This also explains why the smell of garlic often lasts longer than expected.

To reduce the garlic smell, consider the following methods:

• Use cooked garlic instead of raw garlicAfter heating, the spiciness and aroma components are significantly transformed, resulting in a milder flavor;
• Eat with mealsEating it with other foods can reduce the concentration of residue in the mouth;
• Clean your mouth immediately after eatingBrushing your teeth, rinsing your mouth, and using dental floss can reduce residue in your mouth (but cannot eliminate some that is exhaled and expelled through the skin).
• Avoid eating raw food before important occasionsThe peak of garlic flavor usually occurs half an hour to several hours after eating, so you can choose whether or not to include it in your meal.

6. Can eating garlic repel mosquitoes?

The original text mentioned that "in the hot summer, consuming garlic in moderation can also have a certain effect in repelling mosquitoes and insects." This point requires special clarification:Currently, there are no reliable human studies showing that eating garlic is effective in repelling mosquitoes.Existing research mainly focuses on the application of garlic extract in fabric finishing or livestock (e.g., to repel flies and ticks), which is completely different from the idea that "people who eat garlic will not be bitten by mosquitoes."

Therefore, this statement should be classified as accurate.Folk traditionIf you are in an area with many mosquitoes (especially outdoors or in the countryside), the most practical approach is to wear long-sleeved clothing, use mosquito repellent containing effective mosquito-repelling ingredients, and eliminate stagnant water. To learn more about the practical role of garlic in our daily diet, please read more on this website.Four common spices: scallions, ginger, chili peppers, and mustard.〉。

7. Who should be paid special attention to?

Garlic is a pungent food and not everyone is suitable for consuming large quantities. The following groups should be mindful of the quantity and preparation method:

Table 2: People who need to be mindful of garlic intake and the reasons why

person	Precautions
People allergic to garlic	It may cause skin redness, swelling, and itching; in severe cases, it can lead to difficulty breathing. Consumption should be avoided.
Patients with weak gastrointestinal function, gastritis, or gastric ulcers	The pungent components of raw garlic may irritate the gastric mucosa and worsen discomfort; it is advisable to avoid eating raw garlic on an empty stomach, or to use cooked garlic in small amounts in dishes instead.
People taking anticoagulants or antiplatelet drugs	Examples include warfarin, aspirin, and dabigatran. NCCIH refers to garlic supplements.May increase the risk of bleedingYou should inform medical staff and consult a doctor first.
People preparing to undergo surgery or dental surgery	It is advisable to inform your doctor beforehand that you are taking garlic or garlic extract supplements, so that the doctor can assess whether you need to stop taking them.
Pregnant and breastfeeding women	oralHigher than the content of ordinary foodsGarlic may be unsafe, and supplements should not be taken without medical advice.
External use required	NCCIH refers toApplying fresh raw garlic topically can cause severe skin irritation and chemical burns.It is not recommended to apply it to the skin yourself.

1. The claim that "garlic hurts the eyes"

The original text mentioned that for people with eye conditions (such as glaucoma or conjunctivitis), the irritant properties of garlic may worsen eye discomfort. Here, it's important to clarify the specifics:This falls under the category of traditional Chinese medicine theory and folk beliefs.(Traditional Chinese medicine has always classified garlic as a pungent and warm food, and there is a saying that "garlic cures a hundred diseases, but harms only the eyes.")Modern medicine currently lacks high-quality research to confirm that consuming garlic worsens glaucoma or conjunctivitis.。

A more balanced understanding is that garlic does have a pungent effect, and if the eyes are in a state of acute inflammation or discomfort, avoiding large amounts of spicy and irritating foods in the overall diet is a reasonable health practice; however,The treatment of eye diseases such as glaucoma should still follow the diagnosis and medication prescribed by an ophthalmologist."Not eating garlic" should not replace follow-up visits.

2. Regarding interactions with anticoagulants

This point also deserves a balanced explanation. Based on individual case reports and theoretical considerations, the NCCIH warns that garlic supplements may increase the risk of bleeding; however, currently...The results of the controlled studies were inconsistent.—Randomized crossover studies have found that taking garlic concurrently...No significant changePharmacokinetics and efficacy of warfarin (see...)British Journal of Pharmacology researchAnother study of warfarin patients also concluded that garlic extract is relatively safe (see...).Journal of Nutrition Research）。

If you have a history of chronic stomach discomfort, you can refer to the information on this site.Is there a way to completely get rid of chronic gastritis?〉。

8. What are some practical ways to eat on a daily basis?

Garlic is essentially a seasoning ingredient; putting it back into the diet makes it easier to maintain long-term:

• The portion size should be based on the principle of "enhancing flavor".For everyday cooking, about one to two cloves are used each time, which is a mild and sustainable amount. Currently...There is no authoritative organization that has established a daily recommended intake for garlic.Dietary guidelines in various countries do not set limits on this; the key is "moderation and not a substitute for medication." If you plan to consume large amounts of raw garlic extract or high-concentration garlic extract over a long period, it is advisable to consult a doctor or registered dietitian first.
• After chopping or crushing, let it sit for about ten minutes before cooking.Allow alliin and alliinase time to react and produce allicin before cooking.
• There are choices between raw and cooked food.To retain more active ingredients, garlic can be chopped and eaten raw or used in salads, but this can be quite irritating; those with sensitive stomachs should use cooked garlic instead.
• Incorporate it into the overall diet, rather than relying on a single ingredient.Adding garlic to dishes with other vegetables, in line with the overall dietary pattern of "eating more fruits and vegetables," is more beneficial than eating garlic alone.
• Do not use garlic as a substitute for medication or regular treatment.Whether it's for infection, high blood pressure, high cholesterol, or cancer screening, you should follow the advice of your healthcare provider.

IX. Frequently Asked Questions (FAQ)

1. Are allicin and alliin the same thing?

No. Alliin is a tasteless precursor found in whole garlic cloves; allicin is a product generated from alliin by the action of alliinase after garlic cloves are chopped and crushed, and it is also the main source of the pungent aroma and antibacterial activity. The two are related as "raw material" and "finished product".

2. Can eating garlic kill bacteria?

Allicin does exhibit broad-spectrum antibacterial activity in laboratory settings, its mechanism being the binding of sulfhydryl groups (-SH) to bacterial enzymes, thus inactivating them. However, the amount of garlic consumed daily is limited, and allicin is unstable, making it difficult to achieve the concentrations used in laboratory settings. Therefore, while garlic can be a common food ingredient, it cannot replace antibiotics, nor should it be relied upon for "killing bacteria and treating diseases."

3. Can eating garlic fight cancer?

Overall, the evidence does not support this conclusion. Analysis using the FDA's Health Claims Assessment System found no credible evidence to support a reduced risk of stomach, breast, lung, or endometrial cancer; the incidence of stomach cancer in the garlic group was not significantly reduced in randomized trials. However, the study also observed an association with a reduced risk of death from stomach cancer, which is a clue worthy of further investigation. A more conservative approach is to consider garlic as a vegetable and seasoning, but not as an anti-cancer treatment.

4. Can eating garlic prevent or treat a cold?

Currently, only one randomized study meeting the Cochrane inclusion criteria (146 participants, consuming 180 mg of allicin daily) showed fewer colds and shorter duration of illness, insufficient evidence to support or refute its efficacy. Colds and flu are mostly viral infections; the focus should be on rest and hydration. If symptoms persist, medical attention should be sought, rather than relying on garlic for treatment.

5. Can garlic lower blood pressure and cholesterol?

Some studies suggest it may offer minor benefits. A meta-analysis of multiple randomized controlled trials found that garlic lowered systolic blood pressure by an average of 5 to 9 mmHg in people with hypertension; the NCCIH also indicated that garlic supplements may slightly lower total cholesterol and LDL in people with high cholesterol. However, the effect is limited and considered supplementary.It cannot replace medication, nor should you stop taking medication on your own.。

6. Why do I have body odor after eating garlic, and why does it last for a long time?

This is because allicin, which breaks down into methyl allyl sulfide (AMS), is excreted through respiration and skin. Studies using instruments have shown that AMS emissions from the skin peak approximately 30 minutes after ingesting garlic, and then gradually decrease. Brushing and rinsing the mouth can reduce oral residue, but cannot eliminate the portion excreted through respiration and skin.

7. Can eating garlic repel mosquitoes?

There are currently no reliable human studies to support the claim that "eating garlic can repel mosquitoes." Existing research mostly focuses on applying garlic extract to fabrics or livestock. This claim should be categorized as a folk practice; actual mosquito prevention is still more effective through wearing long sleeves, using mosquito repellent, and eliminating stagnant water.

8. How much garlic can you eat in a day?

Currently, there is no authoritative organization that has established a recommended daily intake of garlic. One to two cloves per serving in everyday cooking is a common and mild amount. If you intend to consume large quantities of raw garlic over a long period or take high-concentration garlic supplements, you should consult a doctor or registered dietitian first, especially if you have stomach problems, are taking anticoagulants, or are pregnant.

9. Can people taking anticoagulants eat garlic?

Consult a doctor first. The NCCIH warns that garlic supplements may increase the risk of bleeding; however, controlled studies have yielded inconsistent results, with some randomized studies showing that garlic did not significantly alter the efficacy of warfarin. Given the significant individual variations, the safest approach is to inform your healthcare provider, have your doctor assess your situation, and do not stop or adjust your medication dosage on your own.

10. Why should you wait a while after chopping garlic before cooking?

Whole garlic cloves do not contain allicin; alliin and alliinase must meet after chopping or crushing to form allicin. Letting it stand for about ten minutes allows the reaction to proceed fully; although heating afterwards will still cause some loss of active ingredients, some of the allicin that has already been formed can be retained.

Source of information

• National Center for Compassionate and Integrative Health (NCCIH) <Garlic: Usefulness and Safety>(Evidence strength regarding antibacterial properties, cancer risk, blood pressure, blood lipids, and immune status; safety reminders regarding bleeding risk and external burns, etc.)
• Centre for Health Protection: See a doctor and ask clearly about antibiotics to avoid taking the wrong ones.(Antibiotics are only effective against bacterial infections; colds and flu are mostly caused by viruses and should not be treated with medication on one's own.)
• World Cancer Research Fund (WCRF) <Eat a diet rich in wholegrains, vegetables, fruit and beans>(Allium genus vegetables are non-starchy vegetables; no separate recommendations were made for garlic.)
• U.S. Department of Agriculture FoodData Central(Nutritional content per 100 grams of raw garlic)
• Li WQ et al. BMJ 2019(22-year follow-up randomized trial in Linqi, Shandong: Garlic and the incidence and mortality of gastric cancer)
• Kim JY & Kwon O. "Am J Clin Nutr" 2009(Examining the relationship between garlic and cancer risk using the FDA's health claim assessment system)
• A systematic review and meta-analysis of Front Nutr 2021(Allium vegetables, garlic supplements, and overall cancer risk)
• Medic 2020 meta-analysis(Garlic intake and the risk of colorectal cancer)
• Ried K et al. J Nutr 2016(Updated and integrated analysis of garlic and blood pressure, blood lipids, and immunity)
• Phytomedicine 2015 meta-analysis(Garlic and Hypertension: 7 Randomized Controlled Trials)
• Medic 2018 meta-analysis(Garlic and total cholesterol, LDL cholesterol)
• 《Cochrane Database Syst Rev》2014〈Garlic for the common cold〉(Only one study met the inclusion criteria, insufficient evidence)
• Josling P., *Adv Ther*, 2001(A double-blind randomized study of 146 participants: Allicin supplements and the common cold)
• J Biol Chem 2016(Allicin induces bacterial thiol stress by modifying protein cysteine)
• Front Microbiol 2021 Retrospective(Antibacterial properties and mechanisms of garlic organosulfur compounds)
• Sci Rep 2020(Measurement of diallyl disulfide and methyl allyl sulfide excreted through the skin after eating roasted garlic)
• Br J Pharmacol 2008(Pharmacokinetic interaction between garlic and warfarin)
• J Nutr 2006(Safety study of garlic extract in patients with warfarin)
• Food Chem Toxicol 2013(Short-term heating reduces the anti-inflammatory effect of raw garlic extract)