Geophagia: progress toward understanding its causes and consequences

Geophagia is an ancient practice subject to many prejudices. Recent animal experiments have shed light on its causes and consequences. Geophagia, a form of pica, may be induced by various factors. Clay, the material preferentially ingested by geophagic subjects, interacts with the food bolus and the digestive mucosa. Its capacity to form colloids and to adsorb and exchange ions results in both beneficial and harmful effects. In a less civilized age, the ingestion of clay may have reinforced digestive barriers against alkaloids and toxins, conferring a selective advantage on individuals practicing geophagia. However, in the modern Western world, complex interactions of clay with metals and ions are likely to generate low-level poisoning and deficiencies, potentially damaging the health of geophagic individuals and their offspring.