The different bioactive compound present in vegetables include vitamins, essential elements, dietary fibers, botanic proteins, and phytochemicals. These components of vegetables prevent many metabolic disorders including cardiovascular diseases, diabetes, cancer, dyslipidemia etc. as they have anti-oxidation, anti-inflammation, anti-platelet properties and can also regulate blood glucose, lipid profile, and blood pressure; and thus prevent myocardial damage, hyperglycemia, hypercholesterolemia, free radical induce degenerative diseases and inflammatory conditions1. A wide variety of vegetables are available in nature. Depending upon their characteristics they are grouped in different categories like Allium (onion, garlic), cruciferous (broccoli, cabbage, cauliflower, kale) and dark leafy vegetables (spinach) etc. The vegetables have multiple health benefits due to the presence of different phytochemicals including polyphenols and phenolic compounds. The different types of polyphenols are phenolic acids, flavonoids, stilbenes, and lignans. The health benefits obtained from different vegetable due to these phytochemicals are as follows:
An effect is obtained as the polyphenols inhibits LDL oxidation, increase HDL, and improve endothelial functioning. They also prevent cardiovascular disease due to their antioxidant, antiplatelet, anti-inflammatory effects2.
Mouth, stomach, duodenum, colon, liver, lung, mammary gland or skin cancer preventive effect can be obtained from polyphenols containing vegetables. They have estrogenic/antiestrogenic activity, antiproliferation, induction of cell cycle arrest or apoptosis, prevention of oxidation, induction of detoxification enzymes, and regulation of the host immune system, anti-inflammatory activity and changes in cellular signaling2.
Catechins, anthocyanins are different polyphenols able to lower blood glucose level by inhibiting intestinal glucose absorption and increase the uptake by peripheral tissues2.
Antioxidant/anti-inflammatory properties of polyphenolic compounds may be responsible for exhibit anti-aging effect2.
Oxidative stress and brain macromolecular damage lead to neurodegenerative diseases, including Alzheimer’s disease. Resveratrol and other Polyphenols modulate cellular signaling, apoptosis, proliferation, redox balance and differentiation. The antioxidant property of vegetables enhances neuro defensive effect by stimulating the activity of antioxidant and detoxifying enzymes in the brain2.
Allium vegetables and their health benefits
Garlic, onion, shallot (Alliumascalonicum), leek (Allium ampeloprasum), and chive (Allium schoenoprasum) are different allium vegetables. The different bioactive components present in this group of vegetables are dietary fibers, resistant starch, and fucoidan (carbohydrate), organosulfur compounds, polyphenols, carotenoids, tocopherols, tocotrienols, phytosterols, and isoflavones (antioxidants), unsaturated fatty acids, bioactive peptides, sterols, and phytoestrogens. Phytochemical have several positive bioactivities and able to modulate disease states such as cancer, infection, and metabolic syndrome etc.
Increased intake of allium vegetables is an effective way to prevent cancer risks, such as myeloma, gastric, colorectal, endometrial, lung, prostate and breast cancer. Asian and South American people have higher amount of allium vegetable and have reduced risk of cancer development, whereas the cancer sufferer is more in European populations and they intake less amount of allium vegetable. Therefore, there is a correlation with higher intake of allium vegetable with lower risk cancer development3.
Anticancer effects of Garlic, onion and Chinese chive
- There are four primary organosulfur phytochemicals present in garlic: S-allylcysteine, alliin, S-methylcysteine, and S-ethylcysteine.
- S-allylcysteine acts as an antioxidant, which regulates redox. S-allylcysteine also has anticancer activities due to anti-apoptotic, anti-inflammation, and pro-energetic effect, and regulates signaling capacities.
- S-allylmercaptocysteine with anticancer activity inhibits the growth of cancer cells.
- Organosulfur compounds (OSCs) and Diallyl trisulfide (DATS) are the two bioactive phytochemical present in garlic. Researchers expected that presence of diallyl trisulfide in garlic mainly give anticancer property. Research studies referred that this bioactive phytochemical can induce cell cycle arrest, enhance cancerous cell death, inhibit invasive nature of cancerous cells, prevent spreading of cancer and anti-angiogenesis. Apart from these mechanism diallyl trisulfide can also regulate estrogen and androgens hormonal signaling and able to prevent estrogen induce breast cancer and androgen induce prostate cancer development. A different form of garlic supplements like powder, aged garlic extracts are available in the market and they are effective to decrease the risk of cancer incidence.
- Presence of onions A; fisetin; diosgenin; quercetin in onion has anticancer property
- Chinese chive contains thiosulfinates, tuberoside M, which give cancer preventive effect.
Cardioprotective action of onion, garlic, and Chinese chive
Onion is a widely consumed allium vegetable and is significant to provide cardioprotective action. The phytochemicals like quercetin and catechin present in onion are a potent antioxidant and prevent LDL oxidation and lipid peroxidation by scavenging free radicals. The different mechanism, which supports the cardioprotective effect of onion due to its anti-atherogenic effects are as follows:
- Onion can lessen atherosclerotic lesions
- Hydrogen sulfide (H2S) production is stimulated and anti-apoptotic, anti-inflammatory and antioxidant effects of H2S provides cardio-protection
- Reduce plasma adrenomedulin content, aortic adrenomedulin content and prevent the risk of chronic heart failure incidence
- Activate aortic calcitonin receptor by modifying protein 1/2 mRNAs and thus vasodilatation occurs. Vasodilatation reduces the blood pressure and cardiac load.
- Increase the plasma glutathione peroxidase level, Superoxide Dismutase activity, plasma endothelial Nitric Oxide Synthase activity, and Nitric Oxide content and provide vasodilatation; while reduced production of malondialdehyde, which is produced due to lipid peroxidation and inflammatory response.
- Onion also has blood thinning property1
Similarly, Allicin, allyl sulfides, flavonoids, polysulfides are present in garlic and provide cardio-protective effect and reduce the risks of cardiovascular disease by inhibiting platelet aggregation and lowering cholesterol and blood pressure. Chinese chive contains glycosides, amino-styrene-acrylic acids, which exert cardio-protective action. Therefore, anti-oxidation, anti-inflammation, antiplatelet, lowering blood pressure, improving endothelial function, and attenuating myocardial damage are the main mechanism of onion and other allium vegetables to provide cardio-protective actions4.
Anti-inflammatory effect of garlic and onion
Garlic and onion, both are allium vegetable and have an anti-inflammatory effect; but the different phytochemicals are responsible for this effect. The anti-inflammatory bioactive compound in garlic is S-Propargyl-cysteine, allicin, garlic oil, polysulfides; whereas Quercetin in onion is effect anti-inflammatory agent4.
Anti-obesity effect of garlic and onion
Diallyl disulfide, S-methyl L-cysteine component in garlic and S-Methyl L-cysteine, quercetin component in onion have anti-obesity effect4.
Anti-diabetes effect of garlic and onion
Both garlic and onion can reduce blood glucose level and provide prevention and maintain blood glucose level, as garlic contains anti-diabetic phytochemicals like S-Methyl L-cysteine, S-allylcysteine; diallyl disulphide, S-Allyl-mercapto-captopri; whereas onion contains S Methylcysteine; flavonoids4.
Neuroprotective effects of garlic and onion
Both garlic and onion have neuroprotective effects, as garlic contains N-α-(1-Deoxy-D-fructos-1-yl)-L-arginine, S-methylcysteine, allicin, S-allylcysteine, S-allyl-L-cysteine, diallyl disulfide, diallyl trisulfide, Z-ajoene and onion contains flavonoids, quercetin4.
Immunity boosting effects of garlic and onion
Allyl methyl disulfide in garlic and whole onion extract can boost immunity and prevent different chronic diseases4.
Antimicrobial effect of garlic and onion
Garlic has strong anti-microbial activities as it contains allicin, thiosulfinates, diallyl monosulfide, diallyl disulfide, diallyl trisulfide, diallyl tetrasulfide, ajoene; whereas saponins, Ace-AMP1 in onion also provides the anti-microbial effect. The restriction of microbial growth due to the intake of garlic and onion is due to the presence of this phytochemicals4.
Cruciferous vegetables and their health benefits
Cruciferous vegetables belong to Brassicaceae family. Broccoli, cabbage, and Brussel sprouts are few examples of cruciferous vegetables. Glucose and amino acid content of these plants endogenously produce glucosinolates. After ingestion, myrosinase enzymes able to hydrolyze the glucosinolates and produce isothiocyanates, thiocyanates, and nitriles. These metabolic products of glucosinolates, which is obtained from cruciferous vegetables provide health benefits5, 6.
Antioxidant property - Sulforaphane is a specific type of isothiocyanates and provide anticancer effect due to its anti-inflammatory and anti-oxidant property. The anti-oxidant property of sulforaphane able to reduce the load of reactive oxygen species (ROS), which is responsible for degenerative condition by DNA-damaging, promoting inflammatory signaling etc and accelerates the aging process. The anti-oxidant property of Sulforaphane is mediated through redox-modulating effects. It is believed that low dose of Sulforaphane can able to inhibit oxidative stress and thus Cruciferous vegetables can provide cytoprotective effect5.
Anticancer effect - Research evidence showed that sulforaphane can provide cancer preventive effect, which is significant in case of colorectal cancer. The possible mechanism of action is sulforaphane may modulate miRNAs expression5.
Cruciferous vegetables contain sulforaphane, Indole-3-Carbinol, and its product diindolylmethane. These phytochemicals can block tumor progression by inhibiting signaling networks. Thus Cruciferous vegetables can prevent prostate cancer. The signaling networks inhibition triggers cell cycle arrest and apoptosis. In addition, research also found these two phytochemicals present in Cruciferous vegetables is act as epigenetic modulators in prostate cancer cells and prevent cancer cell development6.
Leafy green vegetables and their health benefits
Spinach is a good example of green leafy vegetable. Spinach contains a high level of flavonoids and has strong anti-oxidant property.
Brain functioning improvement - In a controlled diet measure plan, the spinach extract intake can reverse age-related brain deficit functioning and behavioral improvement is also significant. 
Cardio-protective effect - Spinach has a cardio-protective effect. This leafy vegetable able to reduce cardiac injury, provide the anti-hypertensive effect, increase the antioxidant activity of superoxide dismutase and reduce catalase enzyme activity so that limited ROS can be generated. The antihypertensive activity of spinach is obtained, as this leafy vegetable inhibits angiotensin-converting enzyme (ACE) and renin activities1.
Lettuce is another widely used green leafy vegetable. It also reduces the risk of cardiac diseases by maintaining blood cholesterol level. It can control hypercholesterolemia by reducing the cholesterol synthesis in the liver. It also restricts the dietary cholesterol absorption. The antioxidant property of lettuce can lower lipid peroxidation in the cardiac muscle. It also increases fecal cholesterol excretion. It also decreases LDL level in the blood and improves HDL/LDL ratio. 
- Guo-Yi Tang, Xiao Meng, Ya Li, Cai-Ning Zhao, Qing Liu Hua-Bin Li. Effects of Vegetables on Cardiovascular Diseases and Related Mechanisms. Nutrients 2017, 9, 857; doi:10.3390/nu9080857
- Kanti Bhooshan Pandey and Syed Ibrahim Rizvi. Plant polyphenols as dietary antioxidants in human health and disease. Oxidative Medicine and Cellular Longevity 2:5, 270-278; November/December
- Michael T. Puccinelli, Silvia D. Stan. Dietary Bioactive Diallyl Trisulfide in Cancer Prevention and Treatment. Int. J. Mol. Sci. 2017, 18, 1645; doi:10.3390/ijms18081645.
- Yawen Zeng, Yuping Li, Jiazhen Yang, Xiaoying Pu, Juan Du, Xiaomeng Yang, Tao Yang, Shuming Yang. Therapeutic Role of Functional Components in Alliums for Preventive Chronic Disease in Human Being. Hindawi Publishing Corporation Evidence-Based Complementary and Alternative Medicine. Volume 2017, Article ID 9402849, 13 pages. http://dx.doi.org/10.1155/2017/9402849
- Christopher Dacosta, Yongping Bao. The Role of MicroRNAs in the Chemopreventive Activity of Sulforaphane from Cruciferous Vegetables. Nutrients 2017, 9, 902; doi:10.3390/nu9080902
- Gregory W. Watson, Laura M. Beaver, David E. Williams, Roderick H. Dashwood, Emily Ho. Phytochemicals from Cruciferous Vegetables, Epigenetics, and Prostate Cancer Prevention. The AAPS Journal, Vol. 15, No. 4, October 2013 (# 2013). DOI: 10.1208/s12248-013-9504-4