The onion, also known as the bulb onion or common onion, is a vegetable that is the most widely cultivated species of the genus Allium. Its close relatives include the garlic, scallion, shallot, leek, chive, and Chinese onion
High in Vitamin C, onions are a good source of dietary fiber, and folic acid.
They also contain calcium, iron, and have a high protein quality (ratio of mg amino acid/gram protein).
Onions are low in sodium and contain no fat.
Onions contain quercetin, a flavonoid (one category of antioxidant compounds).
Onions contain organosulfur compounds that may offer unique health benefits.