Garlic can lower levels of bad cholesterol (LDL cholesterol).Fresh cloves or standardized preparations may be used with similar effects. Studies have shown that people who frequently consume relatively large amounts of garlic and onions have lower cholesterol levels than those who don't.When a clove of garlic is crushed or sliced, the active compound alliin and the enzyme allinase are released. Together, they react to form allicin--the main sulfur compound responsible for garlic's health benefits.At least forty clinical studies have measured the effect of garlic preparations on total cholesterol. Most have involved tablets standardized to allicin. Treatments lasted from three weeks to ten months. On average, cholesterol levels decreased 10.6 percent.