In Africa, pregnant and lactating women are able to satisfy the very different nutritional needs of their bodies by eating clay. Often, the clay comes from favored clay pits and it is sold at market in a variety of sizes and with differing content of minerals. After purchase, the clays are stored in a belt-like cloth around the waist and eaten as desired and often without water. The "cravings" in pregnancy for a varied nutritional intake (during pregnancy, the body requires 20% more nutrients and 50% more during lactation) are solved by geophagy.
The clay commonly ingested in Africa contains important nutrients such as: phosphorus, potassium, magnesium, copper, zinc, manganese, and iron.
The tradition of geophagy spread from Africa to the United States with slavery. A 1942 survey in Mississippi showed that...
at least 25 percent of the schoolchildren habitually ate earth. Adults, although not systematically surveyed, also consumed earth. A number of reasons were given: earth is good for you; it helps pregnant women; it tastes good; it is sour like a lemon; it tastes better if smoked in the chimney; and so on.*
Unfortunately, many African-Americans who practice geophagy (or quasi-geophagy) are eating unhealthy material such as laundry starch, ashes, chalk and lead-paint chips because of psychological need. These materials have no nutritional benefits and can lead to intestinal problems and disease. The eating of inappropriate objects and material is known as "pica."
There are good sites for nutritional clay in the Southern United States and sometimes family and friends will send "care packages" of good earth to expectant mothers in the North.
Other Americans, such as the indigenous Pomo of Northern California used dirt in their diet - they mixed it with ground acorn; this neutralized the acid.
* Hunter, John M. "Geophagy in Africa and in the United States: A Culture-Nutrition Hypothesis." Geographical Review April 1973: 170-195. (Page 192)