The parent compound in garlic that is indirectly responsible for health and therapeutic effects is called alliin. In an intact or whole clove of garlic, alliin is inactive, but when the garlic clove is crushed or chopped, the alliin is converted to allicin, a biologically active compound. Allicin will then spontaneously break down into a number of other compounds that have health promoting effects. Allicin also gives garlic its characteristic smell. The enzyme responsible for this chemical conversion is called alliinase. In the past year, researchers have learned important information about the enzyme alliinase. The biologically active allicin is active when it is heated during cooking, therefore it is heat stable. The enzyme alliinase, however, is killed when it is heated. Much of this research is being conducted at Penn State by John A. Milner, PhD

Dr. Milner suggests that when cooking garlic, you should crush or finely chop the garlic and let it sit for at least 10 minutes so that the enzyme alliinase has a chance to work. Again, alliinase only "turns on" when the garlic clove is crushed or chopped. After the garlic sits for ten minutes, cooking garlic shouldn't reduce it's health promoting properties. For example, roasted whole garlic will not possess many health promoting properties. The alliinase enzyme in roasted garlic has not been activated, and alliin has not been converted to allicin. In addition to the active breakdown products produced from allicin, garlic also contains a variety of minerals and vitamins A, B-1, and C.   Allicin contains high levels of sulfur containing compounds that contribute to its health promoting properties. Recently it has been found that other compounds in garlic, called saponins, deliver health benefits as well. Saponins are steroids contained in garlic and these have been associated with cholesterol lowering effects.

Although many studies have tested garlic's health promoting potential, and the herb has been used widely since ancient times, it is important to use caution when eating garlic to prevent and treat medical conditions. More studies are needed to assess what health risks may be connected with therapeutic dosages and to assess the type of garlic preparation and the amount that needs to be eaten to provide maximum benefits.