The world's most used vegetable is the onion. That's a fact. They are used in every culture, from the Egyptians to the Chinese, and along the way it has garnered a mystique unlike any vegetable has ever known.
Onions have long been seen as a source of many good things, from granting eternal life to fighting off disease. I don't know about the eternal life part, but it is true that onions have properties that are beneficial to our health, if not our breath. Aside from being a good source of cancer- and stroke-fighting substances, an onion is easy on the calories, too.
As an ingredient, onions are easy to work with, except for the fumes they emit when cut. We all know that onions make eyes water, but when cooked, our mouths will water as well!