From the article:

This may seem ridiculous, but for certain people, a field of fava beans can spell certain death. Some researchers believe that historical suspicion about fava beans could be rooted in favism, a genetic disorder more common in the Mediterranean than anywhere else. Named for the triggering bean, people with favism develop hemolytic anemia from eating favas, or even inhaling the pollen from its flowers. After consumption or contact, red blood cells start to break down, which can cause anemia-like symptoms, jaundice, and even heart failure. Even today, one out of 12 people affected die of favism. Perhaps Pythagoras had favism, or perhaps not.