Broad Beans: Food of the Dead?

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The ancient Greek philosopher Pythagoras thought that broad beans were the food of the dead. He forbade his disciples to consume or even touch the plants. This turned out to be a fatal policy. When the teacher and his pupils were trapped by an angry mob, they could have escaped through a field of broad beans. True to their beliefs, however, they abjured the beans - and were killed! In the Mediterranean, broad beans are indeed associated with ill health and death. It’s a combination of a particular genetic defect in many Mediterranean peoples, together with a chemical made by the bean plant for its own purposes.

Since broad beans(Vicia faba) originated in the Mediterranean, it is a strange paradox that the inherited disease called ‘favism’ is especially common amongst people with Mediterranean ancestry. As a result of a genetic change, their red- blood-cells contain relatively low levels of a particular enzyme (glucose-6-phosphatedehydrogenase), and cannot tolerate any further reduction in the enzyme. That makes them susceptible to what is known as ‘favism’ but at the same time may provide protection against malaria: if malaria parasites invade, their red- blood-cells die instead of supporting parasite multiplication. (Sickle-cell anemia, originating in Africa, has similar protective action.) The favism mutation may be found in one out of three men in some Sardinian villages, and in two out of three male Kurdish Jews.

The chemical culprit in broad beans is vicine, present in the bean seeds at about 0.35%. Even broad bean pollen contains vicine, which is probably why just walking through a field of broad beans in flower can be so dangerous. Vicine is a moderately effective inhibitor of the red-blood-cell enzyme. In people with already low levels of that enzyme, the red cells burst (haemolysis). The result is a potentially fatal haemolytic anaemia, very similar to malaria. Every spring, when Italian couples go picnicking on the yellow- flowered hillsides, Roman hospitals stock extra supplies of blood, because they know that soon numerous victims will arrive in severe distress, needing urgent blood transfusions.

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