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Garlic contains many compounds, so far more than 2000 having been identified. The most active molecules on health are sulfur compounds, also responsible for its characteristic odor. Allicin is the most studied (part of the S-alk(en)ylcysteine sulfoxide family and derived from cysteine). When garlic is damaged, it releases a particular enzyme – allinase – that converts alliin into allicin (also known more technically as diallylthiosulfinate or propenyl-2-propene thiosulfinate). It is also the action of allinase that gives a particularly strong and volatile smell to allicin, alliin being odorless and tasteless.
In the same way as polyphenols, we can retain that the compound, at the origin of virtues on health, is therefore the result of an aggression of the plant. However, allicin is very unstable. It decomposes quickly in the digestive tract to be transformed into different molecules (ajoenes, vinyldithiines and sulfides), fortunately because it is a particularly toxic molecule for the cell. Garlic also contains polyphenols (mainly apigenin and myricetin) and saponins.
The health benefits of garlic
Garlic has significant antioxidant activity, especially when aged, thanks to its water-soluble sulfur compounds (S-allylcysteine and S-allyl mercaptocysteine).
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Numerous publications have highlighted the cardioprotective effects of regular garlic consumption, including a reduction in blood pressure, plasma LDL-cholesterol levels (by blocking the same enzyme that acts on statins proposed in case of hypercholesterolemia) and triglycerides. Additionally, allicin, and more specifically one of its metabolites – ajoene – helps inhibit platelet aggregation, reduce the risk of atherosclerosis, LDL-oxidized levels and TMAOsynthesis. Regular consumption of garlic also promotes insulin sensitivity.
Another virtue: allicin and ajoene from garlic have demonstrated antibacterial activity (against Salmonella, Escherichia coli, Pseudomonas, Proteus, Staphylococcus aureus, Helicobacter pylori in particular), including activity against certain antibiotic-resistant strains, while promoting the diversity of the intestinal microbiota. They also have antifungal and antiparasitic properties. According to a study, to which 70 Venezuelan soldiers participated, ajoene could even treat the mycosis that causes athlete’s foot as effectively as terbinafine. These properties would be due in particular to the inhibitory activity of allicin against certain enzymes called sulfhydryls. However, most of these studies were conducted in vitro.
It has also been suggested preventive effects of garlic against cancer. In vitro, the growth rate of cancer cells seems to be reduced by blocking their cell cycle. Garlic would be particularly beneficial to help prevent cancers of the liver, prostate, bladder, breast, lung, skin and stomach. According to Professor Sheen’s team, eating 20g of fresh garlic per day (the equivalent of 6 cloves of garlic per week) would reduce the risk of colorectal cancer by 30% and stomach cancer by 50%. These effects would be attributed to a specific sulfur compound – diallyl trisulfide – capable of modulating the activity of certain cell signaling factors. The properties of garlic in cancer prevention also seem to be attributed to sulfur compounds.
Finally, garlic exerts anti-inflammatory effects, particularly beneficial on the intestinal mucosa, in a dose-dependent manner, but also hepatoprotective, and neuroprotective.
In practice, how to consume garlic?
Consuming one clove of garlic per day has significant health effects. However, it is important to consume it fresh and chew it well (yes, you read that right…) to release alliinase and thus form allicin, even if it is not the only beneficial compound for health. The activity of allinase is indeed very fast, the formation of allicin being complete in just 5 min.
Since alliinase is also inactivated at 70°C, I recommend that you do not heat the garlic at high temperatures and add it at the last moment if you are simmering dishes. The residual allicin content is only 16% on average when garlic is boiled. Allinase is also inactivated at pH below 3.5, as can be that of the stomach. The residual amount of allicin in the blood is therefore very low, the vast majority (more than 90%) being eliminated by breathing and perspiration in the form of a compound – AMS – capable of increasing the level of acetone in the breath (the famous bad breath after eating garlic).
Pickled garlic is also an interesting alternative. Consumed in its aged form (more precisely, fermented between 60 and 90 ° C in a very humid environment for 30 to 40 days, sometimes for more than 2 years), the properties are even more marked. Surprisingly, dietary supplements based on garlic powder would have benefits while alliinase is no longer active. One of the hypotheses is that garlic exerts its effects on health primarily thanks to the metabolites of allicin and that the body would have the ability to manufacture this molecule from alliin, even in the absence of alliinase.
Due to its antiplatelet effects, however, garlic should be avoided before surgery in patients with bleeding disorders. Its consumption should also be monitored in case of treatment with anticoagulants or antiplatelets (including aspirin, heparin and warfarin for example).
