Garlic and its Nutritional Health Benefits.
Garlic (Allium Sativum) is a popular spice of the family of Alliums; it is considered a functional spice that acts as a remedy for a variety of ailments because of its diverse array of nutritional constituents, phytochemicals and fibre. It contains high levels of potassium, phosphorus zinc, and sulfur, moderate levels of selenium, calcium, magnesium, manganese, iron, and low levels of sodium, vitamin A, C and B-complex.
Garlic (Allium Sativum) is used widely as a flavouring spice in cooking; it has also been used as a medicine throughout ancient and modern history; Garlic is known for its medicinal uses as an antibiotic, anti-thrombotic and antineoplastic agent. It has been taken to prevent and treat a wide range of conditions and diseases. Garlic has acquired a reputation in different traditions as a prophylactic as well as therapeutic medicinal plant. Ancient Chinese and Indian medicine recommended garlic to aid respiration and digestion, and to treat leprosy and parasitic infestation. Research and books recommended garlic as a useful compound in treatment of arthritis, toothache, chronic cough, constipation, insect bites, gynecologic issues, as well as in infectious diseases (as antibiotic). Several experimental and clinical investigations suggest favourable effects of garlic in its uses.
Clinically, garlic has been evaluated for lowering blood pressure, cholesterol and glucose concentration, as well as for the prevention of arteriosclerosis and cancer. Further properties of garlic compounds have contributed to
i) the reduction of risk factors for cardiovascular diseases,
ii) its antioxidant effect,
iii) its antimicrobial effect and
iv) the detoxification of foreign compound and its hepato-protection properties.
Garlic contains bioactive compounds, particularly polyphenols, flavonoids, flavanols, polysaccharides, sulfur-containing compounds, enzymes (like allinase), and other compounds, such as phellandrene. Garlic contains at least thirty-three sulfur compounds, several enzymes and seventeen amino acids. It contains higher concentrations of sulfur compounds than any other Allium species. The sulfur compounds are responsible both for garlic's pungent odour and many of its medicinal effects. Sulfur compounds in garlic are allicin (the principal bioactive compound present in the raw extract of garlic), alliin, ajoene, allylpropyl disulfide, diallyl trisulfide (DATS), S-allylcysteine (SAC), vinyldithiins, S-allylmercaptocysteine and others.
Bioactive compounds are present in small quantities in foods, mainly in fruits, vegetables, and whole grains, and provide health benefits beyond the basic nutritional value (Gökmen, 2016). Bioactive compounds are molecules that can present therapeutic potential with influence on energy intake, while reducing pro-inflammatory state, oxidative stress, and metabolic disorders (Siriwardhana et al., 2013). Epidemiological studies indicate that high consumption of foods rich in bioactive compounds with antioxidant activity, including vitamins, phytochemicals, and mainly phenolic compounds, such as flavonoids and carotenoids, has a positive effect on human health and could diminish the risk of numerous diseases, such as cancer, heart disease, stroke, Alzheimer’s, diabetes, cataracts, and age-related functional decadence (Hassimotto, Genovese, & Lajolo, 2009; Siriwardhana et al., 2013)
Anti-Carcinogenic Actions of Garlic.
Research have shown that garlic and its organic allyl sulfur components are effective inhibitors of the cancer process. It is taught garlic and its constituents can suppress carcinogen formation, bioactivation and tumour proliferation. Epidemiological and laboratory studies have shown that garlic consumption reduces the incidence of cancer in the stomach, oesophagus, colon, breast, cervix, skin, uterine and lung cancers. Some of the hypothesised mechanisms of the anticarcinogenic effects of garlic are through:
· the scavenging of free radicals,
· increased glutathione levels,
· increased activities of enzyme such as Glutathione S-Transferase GST and catalase,
· the inhibition of cytochrome p450 2E1,
· DNA repair mechanisms,
· the prevention of chromosomal damage.
Antioxidant Actions of Garlic.
Garlic has strong antioxidant properties due to its nutritional and phenolic compounds. For example, the antioxidant properties of aged garlic extract (AGE) decreased reactive oxygen species, which are produced through increased metabolism or chronic inflammation, thus preventing the endothelial dysfunction, an early marker of atherosclerosis.
Whole garlic and garlic extract exhibit direct antioxidant effects and enhance the serum levels of antioxidant enzymes including catalase and glutathione peroxidase. The sulfur compounds found in fresh garlic appear to be nearly 1000 times more potent as antioxidants than those found in aged garlic extract. Garlic and its constituents protect tissues against radical molecules, oxidative damage and improve organ functions in various animal studies.
Antioxidants are compounds that inhibit oxidation, a chemical reaction that can produce free radicals and chain reactions that may damage the cells of the body. Examples of antioxidants are thiols, or vitamin A or ascorbic acid (vitamin C). Rich sources of antioxidants are fruits and vegetables.
Actions of Garlic on Cardiovascular Health.
Cardiovascular disease (CVD) represents the major cause of death worldwide; Many risk factors affect the development of CVD, including obesity and high blood pressure. Garlic can significantly reduce the risk of atherosclerosis, hypertension, myocardial infarction, and ischemic stroke, thanks to the synergistic effects of its nutritional and phytochemical components. From a dietary approach, garlic has a potent role in the prevention and treatment of atherosclerosis and myocardial infarction, as demonstrated by a randomized trial performed with aged garlic extract (AGE) on adipose tissue surrogates for coronary atherosclerosis progression, that reported a decrease of the coronary atherosclerosis growth at dose of 250 mg AGE daily for 12 months by reducing adipose tissue. In addition, isoflavonoid-rich garlic herbal preparation blocked atherosclerosis progression 1.5-fold in postmenopausal women at a dose of 500 mg for 12 months after administration. Moreover, garlic extract (GE) administrated at 400 mg per day for three months modified the markers of endothelial function such as cholesterol (total, LDL, HDL) and triglycerides as well as suppressed chronic inflammation in obese individuals.
Also, garlic powder, aged garlic and garlic oil have demonstrated antiplatelet and anticoagulant effects by interfering with cyclo-oxygenase-mediated thromboxane synthesis.
Immune cells are responsible for the anti-inflammation response; aged garlic contains various compounds that can improve immune systems by modulating cytokine production. For example, the consumption of aged garlic supplementation at a dose of 2.56 g per day for 90 days increased the activity of immune cells in clinical trials, such as γδ-T and natural killer (NK) cells and decreased inflammation by reducing TNF-α and IL-6 in obese adults. Interestingly, the same dose of garlic extract boosted immune cell function, decreasing the severity of cough and flu.
Safety of Garlic.
In humans, garlic is considered safe by the US Food and Drug Administration. However, it is acknowledged that garlic may cause gastric irritation and other side effects only if consumed in high quantities by sensitive individuals. In randomised controlled trials, side effects in sensitive individuals included heartburn, nausea, vomiting, diarrhoea, flatulence, bloating, mild orthostatic hypotension, flushing, tachycardia, headache, insomnia, sweating and dizziness as well as offensive body odour.
Picture adapted from Ansari et al. (2020)
Schematic representation of garlic modulation of biomarkers in cancer, antioxidant activities, cardiovascular disease, bone, inflammation, and metabolic disorders in clinical trials. The symbol (↓) denotes reduced activity and (↑) denotes increased activity.