Health Benefits of Onion - Onions are loaded with plant chemicals including flavonoids, which have both an antioxidant and anti-inflammatory effect. Onions, garlic, shallots, and leeks are all members of the Allium genus.  The average person consumes 20 pounds of this strong vegetable annually, whether they eat it raw, cooked, pickled, or powdered.  Onions come in a wide range of colours, including yellow, red, white, purple, Spanish, and Vidalia.