How Does Garlic Lower Blood Cholesterol?
For over 3,000 years, people have used garlic to cure what ails them. From skin diseases to tumors, from arthritis to the Black Plague, the "stinking rose" has been touted for its healing powers.
In recent years, medical science has caught up with popular wisdom. Epidemiological studies suggest that garlic consumption may reduce the risk of various cancers, as well as enhance immune function and suppress infectious disease. However, much of garlic's recent claim to fame has come from its reputed ability to decrease blood pressure and lower blood cholesterol levels.
Yu-Yan Yeh, Penn State professor of nutrition, has been tracking the cholesterol connection for over a decade, all the way to what looks like the exact mechanism behind garlic's cholesterol-busting effect. At a recent University Park colloquium, he summarized the chain of experiments that have led to this discovery.
Yeh's first step, "to establish the rationale for the subsequent studies," he explains, was to feed two groups of rats a high-fat diet, supplementing one group's chow with Aged Garlic Extract (AGE) made by soaking fresh garlic in alcohol for four to five months to leach out the chemical compounds and remove the smell.
"The AGE supplements reduced total cholesterol by 15 percent," he said, and knocked down triglycerides by 30 percent. This result "was consistent with other studies with other animal species."
Moving on to humans, Yeh asked 34 middle-aged men with slightly high cholesterol to take AGE capsules with their regular diet. After five months he observed a 7 percent drop in total blood cholesterol, and an 8 percent drop in LDL, or "bad," cholesterol.
Next, Yeh conducted in vitro studies to identify the active ingredients responsible for lowering cholesterol. He tested a total of 17 sulfur-containing compounds present in garlic: 11 that are water soluble and 6 that dissolve in fat. Of the compounds tested, Yeh identified three water-soluble compounds that decreased cholesterol in rat liver cells by 40 to 60 percent. These compounds, s-allyl-cysteine (SAC), s-ethyll-cysteine (SEC), and s-propyl-cysteine (SPC), "are the predominant active ingredients" that inhibit the making of cholesterol in the liver, he said.
Yeh's most recent work has focused on understanding exactly how these compounds do their stuff. Experiments on rat liver cells suggest that they depress the activity of a particular enzyme called HMG-CoA reductase, which is the crucial catalyst for cholesterol biosynthesis.
The process is the same, Yeh noted, as that used by popular cholesterol-lowering drugs such as Lipitor, Zocor, and Crestor. While he acknowledged that these so-called statins are much more potent in their effect than AGE, lowering cholesterol levels by about 50 percent, he also pointed out that they can produce serious side effects, including liver damage, while garlic is virtually non-toxic.