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.
