Garlic is closely related to onions, leeks, shallots, scallions, and chives. For many years, it's been claimed that garlic can help fight cancer and infection. It's also said that garlic may be beneficial for stomach and abdominal problems.
Garlic contains many sulfides, one of which is alliin. When garlic bulbs are crushed, alliin is converted to another compound, allicin. Allicin seems to be one of the main active compounds in garlic and gives the root both its odor and its health benefits. Garlic also is an antioxidant.
Garlic may reduce the levels of Helicobacter pylori, a bacterium that can cause stomach ulcers and has been linked to stomach cancer. Other research results on the beneficial effects of garlic on cancer have been mixed.
There are many opinions on how the preparation and amount of garlic eaten may affect your health. Cooking a clove of garlic or cutting it changes the amount and type of the garlic's active compounds. Because of this, some people suggest eating it raw.
Eating large amounts of garlic, especially raw, may irritate your gastrointestinal tract, causing stomach upset and gas. But using a couple of cloves in pasta sauce, in salad dressing, or on garlic bread, even every day, shouldn't be a problem.