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Stanford Report, January 15, 2003

Fresh or capsuled? Researcher studies garlic’s potency as a supplement


What good is garlic? And to reap any benefits, should you eat it in its odiferous fresh form or will a stink-free capsule suffice? Christopher Gardner, PhD, a researcher at the Stanford Center for Research in Disease Prevention, is on a mission to find out.

Thanks to a grant from the National Institutes of Health, Gardner is conducting the most rigorous study ever to address a lingering controversy in the nutritional-supplement field: whether fresh garlic and garlic supplements — a widely consumed herbal supplement — lower cholesterol as claimed.

Food service workers carefully peel garlic in preparation for an unusual study conducted by Christopher Gardner. Gardner and his team are comparing the effectiveness of garlic taken in supplement form to garlic eaten fresh. Study volunteers must agree to eat a number of garlic-infused specialty sandwiches. PHOTO: COURTESY OF CHRISTOPHER GARDNER

In preparation for the study — which is seeking volunteers and entails eating gourmet sandwiches six days a week — Gardner’s staff spent two weeks peeling, mashing and measuring 150 pounds of fresh garlic. That’s on top of the weeks they spent taste-testing a dozen custom-made sandwiches ranging from Portobello mushroom to chicken quesadilla.

The Stanford study differs greatly from the dozens of garlic studies conducted over the past four decades, Gardner explained.

While previous studies tested different garlic preparations with inconsistent and often inadequate potency, the Stanford researchers know the exact chemical composition of the garlic preparations they’re using and will monitor this throughout the study with periodic chemical analyses. And unlike previous studies, which tested just one garlic type, the Stanford study will evaluate the effects of two top-selling garlic supplements along with fresh garlic.

"This study goes far beyond the other trials, because we know exactly what we’re giving participants," said Gardner, assistant professor of medicine. "These results should help set the record straight."

For centuries, garlic has been touted for its disease-fighting properties. The most commonly claimed benefit is reduced cholesterol, although garlic is also said to reduce blood pressure, boost antioxidants and reduce the risk of certain cancers. Seeking such benefits without eating (or smelling like) garlic, millions of Americans take garlic supplements — pills containing powdered garlic or aged-garlic extract.

Meanwhile, researchers sought to determine whether garlic deserves its reputation. More than two dozen studies in the 1970s and ‘80s claimed to prove that garlic lowers cholesterol, but the studies were later criticized for poor design. They involved too few participants or didn’t include a control group, for example. When more-rigorous studies were conducted in the 1990s, most concluded that garlic offered little to no significant benefit.

Gardner said the question remains unsettled because chemical analyses conducted by Larry Lawson, PhD, a biochemist and co-investigator for Stanford’s study, revealed serious flaws in the formulations of the garlic supplements used in past studies. The key issue is allicin, an enzyme that is garlic’s active ingredient.

When a person eats fresh garlic, allicin is released by chewing or mincing the herb. It’s more challenging to get allicin from a garlic pill, however. In some cases, if the pills dissolve in the stomach, the garlic enzyme needed to produce allicin becomes inactivated.

Some pills, meanwhile, have an enteric coating, and these pills often pass through the body undissolved. "The problem is, all these studies didn’t really test garlic — they tested garlic supplements," Gardner said. "That’s not the same as eating garlic."

To select the fresh garlic for the study, Gardner traveled to Gilroy, Calif., the nation’s "garlic capital." An eight-person team spent two weeks peeling and mashing the garlic, then scooping it into 5-gram containers.

The premeasured garlic portions will be spread onto the gourmet "study sandwiches" that participants in the "fresh garlic group" must eat six days a week.

All other participants must eat the sandwiches as well, but minus the garlic. The six types of sandwiches used in the study were chosen in taste tests from a larger sample all custom-prepared by a chef. "This isn’t your typical clinical trial. It’s a lot of fun," Gardner said.

Participants in the Stanford study — 200 healthy adults with moderately elevated cholesterol — will consume the sandwiches along with study tablets for six months. Random assignment will be used to determine which combination of sandwich and pill will be given to each participant in the trial.

Participants’ cholesterol, blood pressure, blood-clotting ability and antioxidant levels will be monitored periodically.

Volunteers must be between ages 30 and 65 and in good health but have moderately elevated cholesterol (LDL of 130-190). And, they must agree to eat their allotted "study sandwiches" six days a week.

"We only want people who like our sandwiches," Gardner said, adding, "We’ve gone to enormous lengths to make sure they’re excellent."

Interested volunteers should call 725-5018 for more information.

Researchers investigate ginkgo biloba's effects on peripheral artery disease (7/24/02)

Nutrition study seeks to lower cholesterol (1/14/98)