eaten in west Africa. In Haiti, poor people are known to eat mud biscuits made from soil, salt, and vegetable shortening. These biscuits hold minimal nutritional value, but manage to keep the poor alive. However, long-term consumption of the biscuits is reported to cause stomach pains and malnutrition, and is not recommended by doctors. Bentonite clay is available worldwide as a digestive aid; kaolin is also widely used as a digestive aid and as the base for some medicines. Attapulgite, another type of clay, is an active ingredient in many anti-diarrheal medicines. Impact on health Clay minerals have been reported to have beneficial microbiological effects, such as protecting the stomach against toxins, parasites, and pathogens. Humans are not able to synthesize vitamin B12 (cobalamin), so geophagia may be a behavioral adaption to obtain it from bacteria in the soil. Mineral content in soils may vary by region, but many contain high levels of calcium, copper, magnesium, iron, and zinc, minerals that are critical for developing fetuses which can cause metallic, soil, or chewing ice cravings in pregnant women. To the extent that these cravings, and subsequent mineral consumption (as well as in the case of cravings for ice, or other cold neck vasoconstricting food which aid in increasing brain oxygen levels by restricting neck veins) are therapeutically effective decreasing infant mortality, those genetic predispositions and the associated environmental triggers, are likely to be found in the infant as well. Likewise, multigenerationally impoverished villages or other homogenous socioeconomic closed genetic communities are more likely to have rewarded gene expression of soil or clay consumption cravings, by increasing the likelihood of survival through multiple pregnancies for both sexes. There are obvious health risks in the consumption of soil that is contaminated by animal or human feces; in particular, helminth eggs, such as Ascaris, which can stay viable in the soil for years, can lead to helminth infections. Tetanus poses a further risk. Lead poisoning is also associated with soil ingestion, as well as health risks associated with zinc exposure can be problematic among people who eat soils on a regular basis. Gestational geophagia (geophagia in pregnancy) has been associated with various homeostatic disruptions and oxidative damage in rats. See also Ampo (snack) Medicinal clay, a variety of clays chosen and used for medicinal purposes, including through consumption References Further reading External links CDC on eating dirt Ethology Cultural anthropology Ethnobiology Eating behaviors