Larry D. Lawson, PhD
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Lawson L.; Garlic for Total Cholesterol Reduction. Ann Intern Med. 2001;135:65-66. doi: 10.7326/0003-4819-135-1-200107030-00029
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Published: Ann Intern Med. 2001;135(1):65-66.
TO THE EDITOR:
To investigate “the effect of garlic on total cholesterol level in persons with elevated levels,” Stevinson and colleagues (1) performed a thorough meta-analysis of trials conducted with garlic supplements. Such an undertaking assumes that consumption of garlic supplements and consumption of garlic cloves result in similar levels of active compounds in the body. However, no clinical trial has yet used a garlic supplement that has demonstrated bioavailability of the probable active compounds of garlic. This is a crucial point because considerable evidence indicates that most of garlic's effect on cholesterol reduction is due to allicin (2), a compound that is readily present when garlic is chopped or crushed but that must be enzymatically formed in the body from alliin when dried garlic is consumed in supplement form. This transformation by alliinase cannot be assumed to take place without bioavailability studies, since alliinase is inactivated immediately by gastric acid and in 1 hour by intestinal proteases (3). Unlike many other brands, the brand used in 10 of the 13 trials that qualified for inclusion in this meta-analysis does not use a coating that protects alliinase from exposure to gastric acid. Because of this, in vivo allicin formation depends on gastric pH and gastric emptying time and is therefore in considerable doubt. The second powder supplement included in the analysis was prepared by spray-drying, a process that results in loss of most of the alliin. Of the two studies that used allicin-derived garlic oils, the one that showed no effect (4) used an unusual solid form of the oil that has since been demonstrated to have low bioavailability in a 48-hour breath test (5). The conclusions derived from this meta-analysis can be applied only to the particular supplement brands used in the studies and not to garlic itself.
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Print ISSN: 0003-4819 | Online ISSN: 1539-3704
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