University Park, Pa. --- Penn State nutrition researchers have identified a group of chemicals in garlic that decreases cholesterol production by liver cells 40 to 60 percent in laboratory tests.
The study is among the first to pinpoint the specific garlic constituents that may be responsible for the cholesterol-lowering effects observed by researchers earlier in both animal and human feeding studies.
Dr. Yu-Yan Yeh, Penn State professor of nutrition, presented the findings today (Nov. 16) at a conference on "Recent Advances on the Nutritional Benefits Accompanying the Use of Garlic as a Supplement" at the Marriott Newport Center, Newport Beach, Calif.
The conference is a continuing and distance education service of the Penn State College of Health and Human Development Department of Nutrition in cooperation with Wakunaga of America Co. Ltd. The conference is supported by Wakunaga, National Cancer Institute and Rexall-Sundown, Inc.
Yeh's paper, "Allyl Sulfur Compounds of Garlic Inhibit Cholesterol Biosynthesis," was one of six offered in the session on Cardiovascular Benefits of Garlic. His co-author is Lijuan Liu, a doctoral candidate in nutrition at Penn State.
Yeh and Liu identified a group of three water soluble, sulfur-containing, garlic constituents (S-allyl cysteine, S-ethyl-cysteine and S-propyl cysteine) that decreased cholesterol production in cultured rat liver cells by 40 to 60 percent.
The Penn State scientist noted that he used fresh garlic extracts in his recent studies. Deodorized aged garlic extract consists mostly of the same water soluble, sulfur-containing chemicals, he said.
In Yeh's earlier feeding studies with rats, aged garlic extract reduced blood cholesterol by 15 percent. In the human studies, 34 men who took deodorized garlic capsules for five months showed a 7 percent drop in total blood cholesterol levels and a 12 percent drop in LDL or so-called "bad cholesterol" levels. High blood levels of total cholesterol and "bad cholesterol" have both been associated with artery and heart disease.
In the current liver cell studies, Yeh and Liu also identified a second group of water-soluble compounds, (glutamate derivatives of S-alk(en)yl cysteines) that depressed cholesterol synthesis by 20 to 35 percent. A third group of water soluble chemicals had no inhibitory effect. A group of fat-soluble, sulfur-containing, garlic constituents depressed cholesterol synthesis only slightly (10 to 15 percent) at low concentrations and, at high concentrations, killed the cells. None of the water-soluble chemicals killed the cells.
"Our current results indicate that the cholesterol-lowering effects of garlic are likely to be from inhibition of cholesterol synthesis in the liver by a combination of the water-soluble, sulfur-containing compounds," Yeh said. "It's not likely that the fat-soluble, sulfur-containing compounds play a major role."
He plans to conduct further research in order to try to identify the specific ways in which the water soluble garlic constitutents he identified interfere with the liver's synthesis of cholesterol.
The results of Yeh's rat feeding studies, conducted in 1994, were published in the journal Lipids, Vol., 29, no. 3. The human studies, conducted in 1997, were published in Food Factors for Cancer Prevention, EDS, Ohigash, H., Osawa, T., Terao, J., Watanabe, S. and Toshikawa, T., Springer, Tokyo, pp. 226-230, 1997.
The current liver cell studies were supported in part by grants from Wakanaga of America Co., Ltd.
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