Onions

Among the many properties afforded Onions in the Old World is the protection from disease. Many folk swear by them, being sure to eat a raw onion every day, the stronger the better. Some say a good onion can protect from undeath, magic, spirits, and just about anything else. They also taste good in a stew, but cooking them is said to take away their power. For the most part, however, they merely make your breath smell.

Source
pg. 20
 * Warhammer Fantasy RPG 3rd ED -- Book of Plague