Onions are very low in calories and fats. 100 grams carry just 40 calories. However, rich in soluble dietary fiber.
Phyto-chemical compounds allium and Allyl disulphide in the onions convert into allicin by enzymatic reaction when its modified leaves are distorted (crushing, cutting, etc). Studies have shown that these compounds have anti-mutagenic (protects from cancers) and anti-diabetic properties (helps lower blood sugar levels in diabetics).
Laboratory studies show that allicin reduces cholesterol production by inhibiting HMG-CoA reductase enzyme in the liver cells. Further, it also found to have anti-bacterial, anti-viral, and anti-fungal activities.
Additionally, Allicin also decreases blood vessel stiffness by facilitating release of nitric oxide (NO) and thereby bring a reduction in the total blood pressure. Further, it blocks platelet-clot formation, and has fibrinolytic action in the blood vessels. Altogether, it helps decrease in overall risk of coronary artery disease (CAD), peripheral vascular diseases (PVD), and stroke.