Allicin
Allicin is an sulphur-containing compound found primarily in garlic. It is the magic essence of the garlic clove - the bite and the garlicky smell that you either love or hate. Allicin isn't actually found in a whole garlic clove. Instead there is a compound called alliin. When the garlic is crushed or chopped, the cells break down and the alliin comes in contact with an enzyme also in the clove, called alliinase. The alliinase changes the alliin into allicin. This is a protective mechanism for the garlic plant. If a clove is damaged or bitten by an insect, the allicin it produces has strong antimicrobial properties which can kill insects and bacteria.
Allicin is a very unstable substance. First of all, the enzyme that causes the change to allicin can be destroyed by heat. Scientists recommend letting chopped garlic sit for ten minutes before cooking it, so that the alliin can be converted to allicin while the enzyme is still active. After it is eaten, the allicin is destroyed by acids so it will not survive the digestive process. Allicin doesn't get absorbed by the body, and it is virtually never found in the urine or in the blood. Other chemicals in garlic which are absorbed by the body have been found to reduce cholesterol and have various health benefits, but the beneficial properties of allicin take place right in the digestive tract.
Studies show that allicin can inhibit the growth of Helicobacter pylori in the gut. This bacteria is responsible for gastric ulcers, and people with Helicobacter pylori in their gut are at a higher risk for stomach cancer. This may explain why groups of people who eat a lot of garlic have a lower rate of stomach cancer. Studies suggest that allicin may also protect against colorectal cancer. Allicin may also protect against other harmful bacteria, certain parasites, viruses and fungi. It has been applied topically to treat fungal infections such as athletes foot, or yeast infections, but you need to be careful with this because it can cause burns.
Garlic contains many other beneficial chemicals besides allicin, in fact allicin itself breaks down into several organosulphur compounds. It is difficult to separate exactly which of these compounds is responsible for each of the many health benefits of garlic. Garlic is used as a folk remedy for conditions such as treating alopecia (hair loss), and as a mosquito and tick repellant. It is being studied for its effects on high blood pressure, improving circulation in the legs, upper respiratory infections, pre-eclampsia, prevention of cancers besides the digestive tract, lowering blood sugar for diabetics, sickle cell anemia, hypercholesterolemia, use as a blood thinner, and atherosclerosis, for starters.
Further studies need to be done in just about all of these areas, but it is difficult to set up human studies with garlic because there are so many different ways that it can be taken - as fresh garlic, prepared many different ways, garlic powder, garlic oil, powdered garlic, dried garlic and something called "aged garlic extract". The amount of organosulphur compounds differs depending on the preparation. For example, powdered garlic or garlic which has been roasted whole contain virtually no allicin. Garlic supplements are also available but they vary widely in the amount of allicin and other organosulphur compounds that they contain.
Just about the only reason not to eat garlic is because of its properties as a blood thinner. If you are taking blood thinning medications, or scheduled to have surgery, this could be a complication. Oh, and some people are bothered by the body odor of a garlic eater. Aside from that, this is a delicious way to keep your digestive tract healthy, and maybe help prevent lots of other illnesses.
The information on this page is not meant to be used in treatment of medical conditions. Please seek the advice of a physician about any medical condition or symptom. Those with medical conditions should consult a medical professional about the appropriateness of taking dietary supplements or diet therapy, and how these methods will interact with their medications.
Phytochemical Society of North America
Phytochemical Society of Europe
For detailed information about the chemical structure, formula, and molecular weight of various phytonutrients, visit
The US Dept of Agriculture.
Phytochemicals also gives detailed information on specific phytochemicals.
Search for herbs at the Sloan Kettering Memorial Cancer Center website.