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Ask Healthy Living: Should I Let Garlic Sit Out Before Cooking It?

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Is it true that cooking garlic decreases its health benefits, but leaving it out to sit for a few minutes before cooking protects its healthfulness?

Garlic's reputation as a health food comes from its contribution of organosulfur compounds to the human diet. Organosulfur compounds are notable because they have the potential to protect against conditions such as heart disease and cancer, though the mechanisms for how are not yet completely understood.

Lab research, for instance, shows that organsulfur compounds could inhibit platelet aggregation, and have antioxidant properties; other studies have shown that these organosulfur compounds in garlic may have anti-inflammatory effects and might even stop the synthesis of cholesterol. Observational studies in humans have also shown an association between garlic consumption and decreased risk of cancer.

One of the key enzymes in garlic that is integral in the formation of these organosulfur compounds is alliinase, which is released when you chop or crush garlic. Some research has suggested that heat inactivates alliinase, or suppresses its potential health benefits.

For example, a 2001 study in the Journal of Nutrition showed that heating garlic in the microwave for 60 seconds or in the oven for 45 minutes seemed to affect garlic's ability to protect against a carcinogen in rats; however, letting the garlic "stand" for 10 minutes before heating it up in the microwave seemed to help retain some of its anti-cancer effects. Another study, published in 2007 in the Journal of Agricultural and Food Chemistry, showed that heating uncrushed garlic for six minutes suppressed its ability to inhibit platelet aggregation.

So given all this information, should we always be leaving garlic out to sit before cooking it, in order to retain its health benefits?

We asked Dr. Ernest Hawk, MD, MPH, a cancer prevention spokesman for the American Association for Cancer Research and vice president and division head of Cancer Prevention & Population Sciences at the MD Anderson Cancer Center, to explain what this research means for every day life. He notes that given the evidence in the lab and in animals, there's theoretically "a rationale to crushing or chopping the item and letting it sit out for a period of time in order to reap the potential benefits of these organosulfur compounds."

But it's too soon to make health recommendations or to say that science proves that leaving garlic to sit out before cooking it can protect its anti-cancer abilities. A randomized control study in humans would be necessary before being able to make those claims, he said.

However, there's essentially no harm in letting garlic sit out for 10 minutes before cooking it, just in case it does boost its healthfulness. "There's no reason to avoid doing so," he says.

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