Garlic (Allium sativum ) reigns as a powerful -- and pungent -- leader among herbal remedies. A close cousin of onions, leeks, and shallots, garlic has traditionally been used to fight off everything from colds and infections to vampires and evil spirits. It's also one of the most intensely studied herbs; over the last 20 years, more than a thousand papers have been written about the "stinking rose" and its relatives.
What is it good for?
Garlic is currently under scrutiny for its potential to reduce the risk of heart disease, cancer, and even food poisoning. Several human studies have found that a daily dose of fresh garlic or some garlic supplements can modestly reduce cholesterol levels, a major risk factor for heart disease, for up to 3 months. However, a 6-month study of various forms of garlic, published in the Archives of Internal Medicine in 2007, found no beneficial effect among adults with moderately high cholesterol levels.
Population studies have found people who regularly ate garlic had lower rates of colon, prostate, esophageal, pancreatic, breast and stomach cancers. A 5-year clinical trial with 5,000 Chinese men found that garlic and selenium supplements reduced the incidence of stomach cancer by 52 percent. However, another clinical trial involving the use of garlic oil in people with precancerous stomach lesions found no effect on the incidence of gastric cancer. Another trial in Japan found that garlic supplements reduced the incidence of non-cancerous colorectal tumors.
Finally, adding a clove of fresh garlic to your burger may help protect you against unfriendly bacteria such as E. coli.
How does it work?
The sulfur compounds that give garlic its trademark odor are probably also responsible for its benefits. Crush a garlic clove and you start a chemical reaction that produces allicin, an antibacterial compound that has killed nasty stomach bugs in laboratory tests. Allicin and its byproducts might help protect the heart by lowering cholesterol levels and thinning the blood.
As for how garlic might help to fight cancer, the National Cancer Institute notes that its protective effects could come from its antibacterial properties or its ability to block the formation of cancer-causing substances, enhance DNA repair, or reduce the proliferation of cancerous cells.
How safe is it?
Garlic has an excellent safety record, but don't overdo it. Eating more than five cloves of garlic daily can cause upset stomach, flatulence, nausea, and heartburn, and some people are allergic to the herb. Also, because garlic extract may keep blood from clotting, you shouldn't use it if you're already taking drugs to thin your blood, such as Coumadin (Warfarin). People being treated for HIV disease should talk with their doctor before using garlic. It has been found to reduce the effectiveness of an anti-HIV drug called Fortovase/Invirase (Saquinavir). Be careful about using fresh garlic on your skin, it can cause serious burns.
What's the best way to take it?
The best form of garlic is raw cloves. Since cooking partly destroys the ability of garlic to produce allicin, you have to eat garlic raw to get most of its benefits. But by cutting open a garlic clove and letting it sit for several minutes before cooking it, you can still get many of its benefits. In addition, many of the studies that showed a beneficial effect used garlic supplements that you'll find in pharmacies and health food stores. Some researchers recommend taking tablets that are enteric-coated; the coating allows the pills to pass through the stomach to the small intestine, where the allicin can be released in a useful form. Keep in mind that the government does not regulate herbal supplements, so quality and potency may vary from product to product. Also, if garlic does help fight cancer, scientists do not yet know how much is needed to lower cancer risk.
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