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Definition: garlic from Philip's Encyclopedia

Bulbous herb native to S Europe and central Asia. It has onion-like foliage and a bulb made up of sections called cloves, which are used for flavouring. It is also claimed to have medicinal properties. Family Liliaceae; species Allium sativum.


Summary Article: Garlic (Allium sativum)
from The A-Z Guide to Food as Medicine
definition

Edible lily family bulb that is a common culinary ingredient. When cut or crushed, it produces allyl sulfur compounds such as allicin, methyl allyl trisulfide, and diallyl trisulfide, each of which may have unique health properties. Other phytochemical constituents include vanillic acid, flavonoids, and terpenoids. Garlic is among the oldest of all cultivated plants and has been used for culinary and medicinal purposes for thousands of years.4 Allicin is partly responsible for the flavor and odor of cut garlic.5

Allicin was previously considered to be a key bioactive constituent of garlic but was found to be highly unstable when processed. It quickly transforms into a variety of other bioactive organosulfur compounds when processed; hence, freshly crushed garlic may contain only limited amounts of allicin and commercially available processed garlic preparations do not contain allicin.5 The biological activity of garlic is likely due to several components, which may include organosulfur transformation products of allicin.

scientific findings

Although preliminary research demonstrated a relationship between garlic consumption and a slight reduction in blood cholesterol level and that garlic may slow the progression of atherosclerosis,6 fresh garlic, dried powdered garlic tablets, and aged garlic extract tablets were all found to be ineffective at lowering serum cholesterol in a controlled trial,6 and a meta-analysis representative of available evidence on the effects of garlic on serum cholesterol from randomized controlled trials found no beneficial effect of garlic on serum cholesterol.7 The same meta-analyses found the methyl allyl trisulfide component of garlic may be antithrombotic.6 Garlic may reduce cardiac arrhythmias.8 Some evidence has suggested that garlic consumption may slightly reduce blood pressure, particularly in people with high blood pressure6; other evidence does not support an appreciable effect of garlic in reducing blood pressure in people with high blood pressure.9 Taking low doses of garlic powder orally, 300 mg/day, lessened age-related decreases in aortic elasticity, while higher doses of 900 mg/day seemed to slow development of atherosclerosis in both aortic and femoral arteries when used over a 4-year period.10 Laboratory studies support that garlic, and or some of its allyl sulfur compounds, suppress carcinogen formation, carcinogen bioactivation, and tumor proliferation.11 Diallyl trisulfide exhibited chemoprotective properties experimentally.12 However, a review on the effects of garlic consumption and various cancers found “no credible evidence to support a relation between garlic intake and a reduced risk of gastric, breast, lung, or endometrial cancer,” and very limited evidence of a relationship between garlic consumption and a reduced risk of colon, prostate, esophageal, larynx, oral, ovary, or renal cell cancers.13 According to the National Cancer Institute, “Preliminary studies suggest that garlic consumption may reduce the risk of developing several types of cancer, especially cancers of the gastrointestinal tract. Most of the studies evaluated different types of garlic preparations and used them in varying amounts.”14 Garlic's antifungal properties have been demonstrated in laboratory research.15, 16 In laboratory studies, aged garlic extract, but not fresh garlic extract, exhibited antioxidative activity.17 Garlic components exhibited neuroprotective properties in experimental research.18 In laboratory studies, allicin and compounds into which it transforms when processed, exhibited antimicrobial properties,19 and treatment with allicin arrested human mammary cancer cells in a laboratory study.20

bioactive dose

Not known. A dose of fresh garlic 4 g (approximately one clove) once daily has been used to treat hyperlipidemia10; for hypertension, the dose of garlic powder 600-900 mg daily has been used.10 If garlic consumption does reduce the risk of developing cancer, the amount needed to lower risk remains unknown.14

safety

Presumed safe when consumed in normal dietary quantities by non-allergic individuals. Raw garlic appears to be safe for most adults and its side effects are generally mild (most commonly, breath and body odor, heartburn, upset stomach, and allergic reactions). Garlic is also an anticoagulant, and therefore, its intake should be considered when monitoring patients with bleeding disorders or on anticoagulants, during or after surgery (garlic use should be stopped 7-10 days in advance of surgery, or if dental work is planned).21 In addition, garlic has been found to interfere with the effectiveness of saquinavir, a drug used to treat HIV (human immunodeficiency virus) infection.6

© 2016 by Taylor and Francis Group, LLC

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