The onion (Allium cepa), also known as the bulb onion or common onion, is used as a vegetable and is the most widely cultivated species of the genus

The onion (Allium cepa), also known as the bulb onion or common onion, is used as a vegetable and is the most widely cultivated species of the genus Allium.Most onion cultivars are about 89% water, 4% sugar, 1% protein 2% fibre and 0.1% fat. They are high in vitamin C, vitamin B6 and folic acid and are a good source of dietary fibre.They are very low in fats and in sodium, and with an energy value of 166kJ (40 kcal) per 100 g (3.5 oz) serving, they can contribute their flavour to savoury dishes without raising the calorific content to any great extent.