Sandy,
Fava beans contain a 'reducing substance'.  Remember oxidation/reduction?
 Persons with glucose-6-phosphate dehydrogenase deficiency (G6PD) or
Mediteranean anemia have difficulty stabilizing the membranes of their
red blood cells.  Feed them a reducing or oxidizing substance, and a
hemolytic crisis ensues (red blood cells fall apart, for the medical
jargon challenged).  Since this is an x-linked recessive, more males are
affected than females, though affected females do exist, since having two
copies of the mutant gene is not lethal.  This condition seems to be most
severe in infancy and childhood.  Fava beans are not the only culprits,
infections, quinine derivatives, and the antibiotic pediazole can all
cause hemolytic crises in individuals with G6PD deficiency.  Raw fava
beans are more problematic than cooked ones.
--
Catherine Watson Genna, IBCLC  NYC  [log in to unmask]