The lowdown on the health benefits of the stinking rose

While recent studies suggest that some people may overestimate garlic’s cholesterol-related benefits, research continues to show that garlic offers other heart-health benefits and may help ward off cancer.

According to a report in the Annals of Internal Medicine that compiled the results of 13 separate, well-controlled studies, garlic can lower blood cholesterol about 4 percent to 6 percent (typically, about 15.7 milligrams in these studies). But in studies in which people also followed a cholesterol-lowering diet, garlic offered no added benefit. A study in the Journal of Nutrition showed a 10 percent drop in LDL (“bad”) cholesterol, but another in the Journal of the American College of Cardiology showed no effect at all.

Garlic may promote heart health without lowering blood cholesterol, however. Several studies show that garlic can decrease clotting tendencies, thus lowering risk of heart attack and stroke. According to the Journal of Nutrition proceedings of a research conference on garlic, test-tube studies suggest that garlic may protect blood vessels by holding LDL cholesterol in a less damaging form, and by blocking undesirable changes in blood vessel walls.

Research continues to bolster the belief that garlic may help prevent certain cancers. An overview of several studies published in the American Journal of Clinical Nutrition showed that garlic lowers risk of colon cancer more than 30 percent and reduces risk of stomach cancer almost 50 percent. Several studies in recent years have also shown that substances in garlic can reduce growth of breast and colon cancer.

Research at Pennsylvania State University shows that compounds in garlic alter body enzymes that activate or detoxify carcinogens, potentially blocking cancer development in many different parts of the body.

HOW MUCH?
How much garlic is needed to receive health benefits? The answer is still not clear, but researchers say that daily use is not needed. Studies generally show that about five cloves of raw or cooked garlic per week is enough to lower cancer risk 30 percent to 40 percent, although some studies have shown similar drops in risk with even one clove a week.

A key point is that the amount of active ingredients in garlic varies, depending on how garlic is used. For example, cooking destroys one form of the substances it contains. But, if raw garlic that has just been chopped stands for 10 minutes before being cooked, the active compounds formed during that period are not destroyed by heat. Garlic powder, if used frequently and generously, may also offer some benefits, but research is still not clear on how good a source it may be.

Use of garlic supplements poses important questions. Supplements do not necessarily provide larger doses of health-promoting ingredients than fresh garlic. The main benefit of supplements is that they don’t have the flavor or odor of fresh garlic that many people don’t like.

BOTTLED OR FRESH?
Garlic supplements come in several forms, and different processes used to produce them may yield products that provide very different levels of active substances. Some studies of garlic and blood cholesterol that showed little benefit appear to have used a garlic supplement that did a poor job of releasing the active ingredient. Other batches of the same brand did not have that problem. This is a reminder that, as with all nutritional supplements, what is listed on the bottle is not always what your body will get.

In view of the research on different forms of garlic, use of fresh garlic in cooking is probably the best route to the benefits garlic seems to offer.

Nutrition Notes is provided by the American Institute for Cancer Research in Washington, D.C.

Written by Karen Collins, R.D. for MSNBC, and published on DrKelley.info, February 20, 2001. Embedded links may no longer be active (Ed. 12.28.10)

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