A reader writes:
Craving dirt or rocks (or sometimes chewing on ice) is a sign of iron deficiency. The reason it's a sign of pregnancy in Kenya but not in Northern Europe is that Kenyan women are much more likely to be anemic due to malaria, hookworm and less meat in their diet. During pregnancy the body's demand for iron increases, thus pica (this type of craving) increases if a woman is already iron deficient.
Yes, I am Kenyan. Yes, I have eaten soil (I have never liked the word dirt). No, I have never been pregnant and no, it wasn't because I was hungry! (You westerners ... we are not all starving!) It is because I am very anemic. The very red rich volcanic soil will do that to you. Especially after the rains. It smells divine.