Allium Vegetables

How They May Benefit Health

By Paul E. Lemanski, MD, MS, FACP

Editor’s Note: This is the 126th in a series on optimal diet and lifestyle to help prevent and treat disease. Any planned change in diet, exercise or treatment should be discussed with and approved by your personal physician before implementation. The help of a registered dietitian in the implementation of dietary changes is strongly recommended.

Medicines are a mainstay of American life and the healthcare system not only because they are perceived to work by the individuals taking them, but also because their benefit may be shown by the objective assessment of scientific study. Clinical research trials have shown that some of the medicines of Western science may reduce the risk of Type 2 diabetes, heart attacks, strokes, cardiovascular death and even some cancers.

In the first 126 installments of the Non-Medicated Life, a healthy diet and lifestyle have been shown to accomplish naturally for the majority of individuals most of the benefits of medications in the prevention of the chronic medical conditions mentioned above. As part of a healthy diet, the inclusion of vegetables from the allium family – garlic, onions, leeks, chives, scallions and shallots – possess both bold, enticing flavors and also potent potential health benefits. This article reviews the key benefits including immune support, heart health, antioxidant power, anti-inflammatory effects, and possible cancer prevention.

The allium family share a common phytochemical heritage, rich in organosulfur compounds like allicin, which give them their characteristic strong aroma. Examples of such compounds include: allicin, its metabolites diallyl sulfides, s-allyl-cysteine (SAC) and s-allyl-mercapto cysteine (SAMC), as well as ajoene. Such compounds, especially allicin in garlic, have antimicrobial properties that bolsters immune function and helps the body fight infections. As early as 1858 Lois Pasteur demonstrated that garlic could kill bacteria. In a real world example, during World War II, the Soviet Army, short on stocks of penicillin, relied on garlic juice and crushed garlic applied to open battle wounds to prevent infection and gangrene. The so called “Russian Penicillin” was also used to treat internal infections.

With regard to heart health, regular consumption of allium vegetables is linked to lower blood pressure, improved cholesterol levels, and a reduced risk of heart disease. These effects appear to result from the organosulfur compounds ability to help relax blood vessels as well as to their antioxidant and anti-inflammatory effects. A 2024 review of animal and clinical data showed: reductions in plasma lipids (9.6 mg/day of allicin reduced total cholesterol by 4.2% and LDL “bad” cholesterol by 6.6%); reduction of homocysteine improved in carotid IMT (intimal medial ratio is an ultrasound measurement of sub-clinical plaque formation in carotid arteries); improvements in endothelial function (promoting a relaxation of blood vessel smooth muscle reducing blood pressure); as well as reduction in oxidative stress – all contributing to a slowing of plaque formation and atherosclerotic progression in blood vessels.

With regard to possible cancer prevention, studies have found that regular consumption of allium vegetables may lower the risk of certain cancers through reduced inflammation, and their ability to enhance DNA repair and reduce cell damage. In in vitro studies organosulfur compounds show: anti-proliferative (slowing cancer growth) and pro-apoptotic (promoting programmed cell death) effects and can block carcinogen bioactivation, induce phase 2 detoxifying enzymes (which increase carcinogen breakdown and elimination) and interfere with tumor growth, differentiation (becoming more malignant), and metastasis (cancer cells moving throughout the body). 

These effects have been observed in multiple cancer cell lines including breast, gastric, glioblastoma (type of brain cancer) and cervical cancer. However, meta-analysis (comparison of data from similar trials) of human clinical trials have had mixed results. Diallyl sulfides have been reported to hinder cell cycle progression (cell aging), induce apoptosis, and inhibit key signaling pathways involved in tumor progression, thus affecting multiple stages of carcinogenesis (the process by which healthy cells become cancerous) and metastasis related processes such as adhesion and invasion. SAC and SAMC may also affect carcinogen metabolism, as well as DNA repair pathways, contributing to potential cancer prevention.

From a practical perspective, it is helpful to discuss dosage ranges and preparation methods that have the greatest likelihood of benefit, with the lowest possible side effects. Trials and reviews of studies of cardiovascular and possible cancer prevention typically use 1-1.5 cloves (3-5 grams) of raw garlic per day, or 600-1,200 mg/day garlic supplement in divided doses, or 1/4 teaspoon of garlic powder/day. It is important to note that garlic in these ranges, while safe for most can represent bleeding risk for those on anti-coagulants (such as warfarin and anti-platelet agents), those with established bleeding risk, or those anticipating planned surgery – most surgical guidelines recommend stopping garlic supplements seven days pre-op. It is strongly recommended that individuals at risk for bleeding discuss the use of allium vegetables or supplement consumption with their primary care physician or surgeon.

In preparation of allium vegetables, in order to maximize available allicin (and its metabolites) absorption, it is best to crush or chop garlic and wait 5-10 minutes before heating. Heating immediately after crushing or chopping can inactivate the enzyme alliinase, which converts the precursor to the active compound. Additionally, quickly sauteing or adding garlic near the end of cooking preserves the more active organosulfur compounds. Using mixed allium vegetables such as onions, leeks, chives, scallions and shallots add complementary organosulfur compounds, as well as the flavonoid quercetin, that provide additional antioxidant and healthful vascular effects.

In summary, the consumption of vegetables in the allium family including garlic, onions, leeks, chives, scallions, and shallots provide cardiovascular benefits of lower cholesterol, lower blood pressure, and improved cardiovascular health with reduced oxidation and reduced inflammation. Evidence for cancer prevention has shown mixed results in observational and clinical trials, and more studies are needed. 

From a practical perspective, one clove of garlic a day, or a 1/4 teaspoon of standard culinary garlic power are generally safe and provide benefit – see above for those at risk from use who should discuss it with their primary care physician or surgeon. Additionally, a serving of onions daily will provide benefit. In this way, the consumption of vegetables in the allium family may help to improve cardiovascular health and possibly reduce cancer risk. 

Paul E. Lemanski, MD, MS, FACP (plemanski3@gmail.com) is a board-certified internist practicing internal medicine and lifestyle medicine in Albany, NY. Paul has a master’s degree in human nutrition, he’s an assistant clinical professor of medicine at Albany Medical College, and a fellow of the American College of Physicians.