Onions, Garlic and Allium Vegetables as Food
What research found on onions, garlic, leeks and other allium vegetables eaten as food, how food differs from garlic supplements, and the safety points to know.
Content last updated . This page has not been medically reviewed.
Safety first. Supplements can cause side effects and interact with medicines. Read mushroom safety and interactions before you use any mushroom product.
Read this first: food versus supplements
This page is about allium vegetables as food. Garlic supplements and extracts carry different risks. NCCIH says garlic supplements may increase the risk of bleeding, and that anyone taking them should tell their health care providers, especially before surgery or when taking anticoagulants or aspirin. [1] NCCIH also warns that fresh raw garlic may not be safe on the skin, and that some people have allergic reactions to garlic. [1] The details are at Garlic in Herbs & Botanicals and How interactions work.Which plants
Allium vegetables are the onion family: onion (Allium cepa), garlic (Allium sativum), leek (Allium ampeloprasum), chives (Allium schoenoprasum), shallots and scallions. A gastric cancer meta-analysis lists onions, garlic, shallots, leeks and chives among them. [2] The U.S. Dietary Guidelines place onions in the "other vegetables" group. [3] The bulb, leaf or stem eaten differs by vegetable. No identification or foraging advice is given here; for plant poisoning questions see Plant and mushroom poisoning and Poison Help (1-800-222-1222 in the U.S.).What research shows
| Question | What the source found | Strength of evidence | Form and people studied |
|---|---|---|---|
| Stomach (gastric) cancer risk | People eating the most allium vegetables had lower risk (odds ratio 0.54, 95% CI 0.43 to 0.65). The authors cite confounding and measurement problems and say more studies are needed. [2] | Observational, mixed | 19 case-control and 2 cohort studies, 543,220 people [2] |
| Stomach cancer, garlic | NCCIH says consuming garlic does not seem to reduce the risk of stomach cancer. [1] | Mixed with the row above | Garlic as reviewed by NCCIH [1] |
| Cancer overview | An umbrella review of 16 meta-analyses found the most beneficial cancer result for gastric cancer (RR 0.78, 95% CI 0.67 to 0.91). [4] | Observational, promising but limited | 16 meta-analyses of allium vegetable consumption [4] |
| Colorectal cancer | NCCIH says it is uncertain whether garlic influences risk. [1] | Insufficient evidence | Garlic [1] |
| Cholesterol | Garlic supplements may reduce total and LDL cholesterol a small amount in people with high cholesterol. [1] | Promising but limited (supplements, not cooking) | Supplement trials; not the same as garlic in meals [1] |
| Colds | Cochrane found insufficient trial evidence on garlic for preventing or treating the common cold. Only one trial met the inclusion criteria. [5] | Insufficient evidence | Garlic supplement trial [5] |
| Onions, leeks and chives alone | Proper evidence not found. We searched PubMed for human reviews of onion consumption and health and did not find onion-specific reviews to report. | Insufficient evidence | Not applicable |
Frequently asked questions
Is garlic good for you?
Garlic is a common food. NCCIH says garlic supplements may lower cholesterol a little, [1] but those results are for supplements. Evidence for garlic as a meal ingredient is mostly observational.
Do onions and garlic lower cancer risk?
A meta-analysis linked high allium intake to lower gastric cancer risk, but it cites confounding and calls for more studies. [2] NCCIH says garlic does not seem to reduce stomach cancer risk. [1] The evidence is mixed.
Does garlic prevent colds?
Cochrane found insufficient evidence. [5]
Can garlic interact with medicines?
NCCIH says garlic supplements may raise bleeding risk, especially with anticoagulants or aspirin, and should be disclosed before surgery. [1] Ask a pharmacist about supplements.
Are raw onions or garlic safe on the skin or as a home remedy?
NCCIH says fresh raw garlic may cause severe skin irritation and chemical burns when used topically. [1] We do not give home-remedy methods.
More details: evidence, limits and cautions
The details behind this page: cautions, limits of the evidence and where sources disagree. Open any note to read it.
Limits and uncertainty
- Eating habits are tangled together. Studies of people who eat more allium vegetables are observational and cannot prove cause. [2]
- Many garlic results come from supplements. The umbrella review also reports cholesterol, blood sugar and blood pressure findings for garlic, [4] and NCCIH describes similar results specifically for garlic supplements. [1] The abstract we read does not say which form of garlic each study used, so these findings should not be read as proof for a clove in a meal.
- Heat, storage and form were not compared in the sources we read, so we make no claim about them.
Safety and who should ask a professional
- Common side effects of garlic eaten or taken by mouth include breath and body odor, abdominal pain, gas and nausea. [1]
- Allergy. Some people react to garlic. [1] See Food allergy basics and emergency signs. Call 911 for trouble breathing or swelling of the face or throat.
- Pregnancy and breastfeeding. NCCIH says garlic may not be safe by mouth in amounts greater than those found in foods. [1]
- Surgery and bleeding. The bleeding caution applies to supplements. [1] Tell the surgical team about any garlic product.
- Gut comfort. Onions and garlic are discussed as prebiotic foods at Prebiotic foods.
References
- NCCIH. Garlic. Read 2026-10-23.
- Zhou Y, et al. Consumption of large amounts of Allium vegetables reduces risk for gastric cancer in a meta-analysis. Gastroenterology. 2011. Read 2026-10-23.
- U.S. Department of Agriculture and U.S. Department of Health and Human Services. Dietary Guidelines for Americans, 2020-2025. Read 2026-10-23.
- Wan Q, et al. Allium vegetable consumption and health: an umbrella review of meta-analyses of multiple health outcomes. Food Sci Nutr. 2019. Read 2026-10-23.
- Lissiman E, et al. Garlic for the common cold. Cochrane Database Syst Rev. 2014. Read 2026-10-23.
Education, not medical advice. This page is for general information. It does not diagnose or treat any condition and is not a substitute for care from a qualified health professional. Natural does not automatically mean safe. Ask a clinician or pharmacist before changing your care, especially if you take medication, are pregnant or breastfeeding, or have a health condition.