Most of us are only exposed to one type of garlic in supermarkets, so don't realize how many varieties there really are, and the various benefits of garlic other than just for cooking. There are generally 11 types of garlic, all giving similar health benefits, but with widely varying flavors.
Garlic originated in south-central Asia thousands of years ago. The area of western China, northern Afganistan and Iran is called the garlic crescent. It was valued then, as it is now, for its flavor, long storage, and certain health benefits. It especially was important then, with its antibacterial properties and strong odor, to both preserve foods and mask rancid smells.
Nomads likely carried garlic to the Mediterranean, where most associate it and where it originally was believed to have come from. The earliest known record of garlic dates back 6000 years to clay artifacts resembling garlic bulbs in Egyptian tombs. Other garlic artifacts have been found in later tombs as well, including bulbs dating to 1500 B.C. Mummies were rubbed with it during embalming. Other references indicate garlic was being used 5000 years ago in India, 4500 years ago in Babylon, and at least 2000 years ago in China.
Garlic spread through trade around the Mediterranean and southern Europe, being better adapted to these warm climates. Garlic was one of the original antibiotics used by Greeks and Romans. With its long history of cultivation in this area, many varieties have come from there. Our original varieties arrived from there in the 1700's with explorers and early colonists.
Other varieties originated from early cultivation in the Caucasus and Eastern Europe. These have led to more recent introductions to this country with Polish and German immigrants. Most recently, the Caucasus region led to a surge in new varieties (for us) when the USDA in 1989 was finally allowed into areas of the Soviet Union previously closed. Story has it that the plant explorers were accompanied by guards, and only allowed to roam at night so not to compromise the security of oil fields and secret missile bases. Varieties often were named for the villages where they were found.
All through this history of garlic, its flavoring and therapeutic uses have come mainly from one chemical, allicin. This chemical can perhaps be remembered from the genus name of garlic, and their close relatives the onions (Allium). It's interesting that allicin doesn't exist in whole garlic cloves, but is formed quickly from two other chemicals that mix when plant cells are crushed. If you've ever smelled or eaten whole garlic cloves, then immediately upon crushing or mincing them, you've seen just how quickly this chemical reaction happens.
Another key point to know is that allicin is destroyed by heat, as in cooking. So if you are after the full health benefits of garlic, you'll need to eat it raw. Biting, crushing, chopping, or slicing will release allicin. Cooking isn't all bad though from a health perspective, as many other sulfur compounds are released when cloves are prepared and aren't destroyed by cooking.
If you do eat raw garlic, studies suggest "a clove a day keeps the doctor away." Raw garlic should be consumed with other food to avoid the possibility of heartburn and stomach upset. Eating more may cause these symptoms, and other side effects. Garlic may interact with certain medicines, like an anticoagulant, so it is best to check with your doctor before beginning a regime of garlic for health. There are many garlic supplements you'll find in vitamin sections of stores, but the research on these and their effects is inconclusive. Of course the most common side effect of raw garlic is the famous "garlic breath", as well as flatulence in some.
So why even consider eating raw garlic, or worrying about destroying its allicin? This sulfur compound, and other similar ones created from breaking the garlic cloves, is an effective antibiotic on many organisms. It may help reduce salmonella that causes some food poisoning, and some intestinal infections including diarrhea. Yet don't store or preserve garlic in oil, as may seem desirable. Oil provides the perfect environment for the botulism bacterium to contaminate this low-acid vegetable, an organism that garlic has no effect on.
Heart-related studies indicate several benefits including possible cholesterol lowering, lowering blood pressure, lowering blood glucose, and providing antioxidant effects that have become more known recently in other foods. Both cooked and raw garlic may help reduce the risk of certain cancers, including gastrointestinal ones. Increasingly, studies are showing that garlic enhances the body's immune system.
If you aren't focused merely on the health effects of garlic, just enjoy it in your cooking. Cooking whole, or roasting, results in a mild, caramelized flavor without the strong aromas. Chopping releases the flavors, then cooking in oil serves to enhance these and form the basis for many types of cuisine including sauces, stews, curries, and stir-fries. Just make sure to not cook too much until dark brown or burned, or it will taste unpleasant. Cooking in oil until straw-colored or tan results in complex and nutty flavors. Don't merely settle for supermarket garlic, but visit local growers and farmers markets for more variety. Better yet, grow your own!