According to Nicole Nisly, M.D., University of Iowa Health Care associate professor of internal medicine, garlic has been associated with preventing colon, stomach, throat and prostate cancers. Nisly suggests a few possible reasons why garlic is thought to be a cancer-preventing herb: it increases natural killer cells that fight cancers, and it works as an antioxidant that protects cells and rids the body of cancer-causing agents.

Besides preventing cancer, garlic has been known to decrease fungal infections and bacteria in the body, lower cholesterol, and decrease the risk of heart disease.

While the exact role of garlic in the preventive process is undetermined, it is believed that when garlic is crushed it forms allicin, which gives garlic its smell. When allicin is formed, it then breaks down further and, depending on how it is prepared, can increase the body’s resistance to cancer. So in order to reap the benefits of garlic, it must be used correctly. Allicin is destroyed by heat and age, so it's best to cook garlic at the lowest temperature possible and the shortest amount of time available.

How much garlic should you consume each day? This varies by how it is prepared. Nisly suggests taking a dose of 0.4 to 1.2 grams in a powder or supplement form. If you are using fresh garlic, prepare 1 clove twice a day or 4 grams once a day.

There are some side effects of garlic besides the strong taste and smell. Some people experience indigestion, intestinal or stomach discomfort (such as bloating or pain), sweating, light headaches, and other allergic reactions.

There are also some drug interactions people must be aware of before taking garlic. Garlic is actually a blood thinner, so it shouldn’t be taken if you are already on blood-thinning medications and people run the risk of bleeding. As a result, patients who are about to undergo or have just finished surgery should not take garlic. Garlic has also been known to decrease the effectiveness of protease inhibitors, so individuals taking HIV drugs should not take garlic.

Supplements can be a beneficial way to maintain a healthy body, but Nisly emphasizes that it is important to remember that dietary supplements do have an affect on your body and that by taking them you run the risk of interactions.

Dietary supplements are not regulated or restricted by the Food and Drug Administration, so different brands may contain different amounts of the product. Therefore, Nisly recommends always using the same brand of supplements. It is important to research the brand you are taking to make sure that what you get in the bottle is the real thing. Many companies have toll-free numbers and Web sites that can help answer questions. If you are still unsure, ask your doctor or pharmacist.

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Nicole Nisly, M.D.