Garlic

Garlic

Garlic (Allium sativum; “שום” in Hebrew) is one of the oldest plants used medicinally, and it appears in ancient Egyptian, Greek and Chinese writings. Nutritionally, the amounts eaten are too small to contribute vitamins or minerals in significant amounts — its value lies almost entirely in bioactive sulfur compounds.

Allicin — why it matters to crush and wait

A whole garlic clove contains no allicin at all. It contains two components that are physically separated from each other inside the cell: alliin (an odorless amino acid) and the enzyme alliinase.

When garlic tissue is damaged — by crushing, cutting or chewing — the two meet, and the enzyme converts alliin into allicin within seconds. This is the substance responsible for the pungent smell and for most of the biological activity.

This leads to the most important practical advice about garlic: the enzyme alliinase is heat-sensitive and is quickly inactivated by cooking. When garlic is thrown whole or chopped straight into a hot pan, its enzyme is inactivated before it has had time to produce allicin, and most of the active potential is lost.

The solution is simple: crush or chop the garlic and wait 10 minutes before heating. During this time allicin forms, and it is much more heat-resistant than the enzyme that produced it. This is a measurable difference that has been demonstrated in laboratory studies.

Allicin itself is unstable and breaks down within hours into secondary sulfur compounds (ajoene, diallyl disulfide and others), which also have biological activity of their own.

Research-based health benefits

• Blood pressure — the best-established benefit: meta-analyses of controlled trials found that garlic — mainly in the form of a standardized supplement or aged garlic extract — lowers systolic blood pressure by about 8 mmHg and diastolic by about 5 mmHg in people with high blood pressure. That is a drop of a similar magnitude to a single drug at a starting dose. In people with normal blood pressure the effect is small or nil. The mechanism includes increased production of hydrogen sulfide (H₂S) and nitric oxide, both vasodilators.

• Lipid profile: trials show a modest drop in total cholesterol and LDL — on the order of 5-10% with prolonged intake. The effect is consistent but modest.

• Antimicrobial activity: allicin has proven activity against bacteria, fungi and parasites under laboratory conditions. An important caveat: the translation to infections in the human body is far more limited, since allicin breaks down quickly and does not reach tissues at the concentrations achieved in the test tube. Garlic is not a substitute for antibiotics.

• Immune function and colds: several controlled trials showed a reduction in the frequency and duration of colds in people taking a garlic supplement. The evidence is of limited quality, and the number of participants is small — a promising finding, but not well established.

• Epidemiological research and cancer: cohort studies link high intake of vegetables from the allium family (garlic, onion, leek) to a lower risk of stomach and colorectal cancer. This is an observational association only, and intervention trials have not confirmed it. It should be presented as a hypothesis, not a conclusion.

• Aged garlic extract (AGE): a form that has undergone prolonged soaking, low in allicin but rich in S-allyl cysteine. It is stable and odorless, and a considerable part of the high-quality clinical research — especially on blood pressure — was actually done on it.

Downsides and health considerations

• Effect on blood clotting — the most important clinical consideration: garlic has measurable antiplatelet activity. Combining it with blood thinners (warfarin, aspirin, clopidogrel) may increase the risk of bleeding. Stop garlic supplements about one to two weeks before surgery, and inform the surgeon. Normal culinary use is not a concern, but high-dose supplements are.

• Body and breath odor: the main compound responsible is allyl methyl sulfide (AMS), which is not broken down in the digestive tract but is absorbed into the blood and excreted through the lungs and skin. That is why brushing your teeth doesn’t solve the problem — the smell lasts for hours and even a whole day. Milk, apple and mint leaves have been shown to reduce it somewhat.

• Heartburn and reflux: garlic relaxes the lower esophageal sphincter and can worsen reflux. It is a known trigger.

• FODMAPs: garlic is rich in fructans and is one of the leading triggers in irritable bowel syndrome. Garlic-infused oil (in which the water-soluble fructans don’t pass into the oil) is an accepted solution on a low-FODMAP diet.

• Contact dermatitis: prolonged handling of raw garlic can cause skin irritation. Don’t apply raw garlic to the skin as a “treatment” — chemical burns have been reported.

• Botulism in oil: raw garlic stored in oil at room temperature creates an oxygen-free environment that allows C. botulinum to grow. Store garlic in oil only in the fridge and for a short time, or buy an acidified commercial product.

Nutrition facts per 100 g (raw)

Note: a garlic clove weighs about 3 g, so its actual nutritional contribution is negligible. The value lies in the sulfur compounds.

Practical use

The key rule: crush or chop, wait 10 minutes, and only then heat. This is the difference between active garlic and merely aromatic garlic.

How much: most clinical studies used standardized supplements, not fresh garlic. In culinary terms, 1-2 cloves a day are a reasonable, accepted amount. Keep in mind that moving from culinary garlic to a high-dose supplement brings the clotting consideration into the picture.

Raw vs. cooked: raw garlic (in tahini, hummus, sauces) retains full activity. Cooked garlic is still beneficial if you waited before heating it.

Black garlic: garlic aged under controlled heat and humidity. It loses its pungency and allicin, but develops a different antioxidant profile and a sweet-umami flavor.

Storage: in a cool, dry, ventilated place — not in the fridge, where humidity encourages sprouting and mold. A clove with a green sprout in the center is safe to eat but more bitter.

Summary

Garlic is one of the cases where folk tradition has a partial but real scientific basis: the effect on blood pressure in people with high blood pressure is established in meta-analyses and of a significant magnitude. The antimicrobial effects are exaggerated in marketing and based mainly on lab work. Two practical things are worth more than everything else: crush and wait 10 minutes before cooking, and be careful combining garlic supplements with blood thinners or before surgery.