“The reason for the presence of sulfur compounds in garlic is to allow the garlic bulb to survive (while it’s) in the ground, where it’s surrounded by predators microscopic and larger,” Block said. The smelly, burning “compounds that are released when the garlic clove is disrupted serve to deter further attack.”
The role of allicin found in garlic
“There is a lot of folklore as to the beneficial health effects of garlic in the diet,” said Alan Slusarenko, a professor of plant physiology at RWTH Aachen University in Germany, via email. “However, we have no data from controlled clinical trials.”
Issue: How to turn allicin into a useful drug
“That’s been the big problem: How do you take this compound allicin, with all these wonderful properties demonstrated in (human) cells, and make it into a useful drug?” Block said.
“To try to translate that into a medicine has proven very, very challenging, and has led a lot of companies — that are out to make money — to make false claims based on the activity of these compounds in cells,” he added. In other words, some companies have been “trying to convince people that just because they’re very active in all these experiments, it’s also active as a pill or as a supplement.”
Allicin is “destroyed” when cooked, Slusarenko said, “and off-the-shelf supplements generally have no or variable contents of allicin.”
And the US Food and Drug Administration doesn’t regulate dietary supplements, so “advertisers can say whatever they want,” Block said.
Possible side effects
Given these issues, you might think that people could just eat raw garlic for health benefits.
However, this isn’t a good idea for several reasons: Because allicin is garlic’s very potent defense, eating raw garlic “can cause severe irritation and burns,” Block said. The slower a person’s metabolism, the more likely it is that they could experience side effects such as rash, heartburn, stomach irritation, and burns in the esophagus or digestive tract.
Some cultures don’t have this problem. In some areas of the Mediterranean, for example, “people will chew on garlic, and I guess they’ve developed a resistance to it,” Block said. But for many others, it’s “dangerous and it should never be used with children. And it should not be used on sensitive areas of the body.”
A positive, not a panacea
Maybe the biggest benefit of garlic isn’t what science has to say about it, but rather how garlic can help us eat better.
“Scientifically, garlic and onions and related plants are really one of nature’s wonders. I think that there’s some very exciting science that one can discover,” Block said.
“It’s possible that, in the future, scientists will discover ways to utilize these remarkable molecules in a way to treat disease. But again, that has to be done using the full power of science to test compounds in a fair and honest way to make sure that they actually work.”
CNN’s Sandee LaMotte contributed to this story.