Geophagia, the intentional and repeated ingestion of soil material, is a complex eating behaviour with incomprehensible aetiology. It is generally assumed that
geophagia may help supplement
mineral nutrients and thus should not be dissuaded, particularly in subsistence communities. This is largely based on the assumption that a large proportion of
mineral nutrients in geophagic materials is potentially available for absorption in the body. We tested this hypothesis on five
soils collected from
geophagia-prevalent communities by using an in vitro soil ingestion simulation test that is broadly similar to the gastrointestinal (GI) tract. The results show that, despite the
soils being rich in
mineral nutrients, soil ingestion, inadvertent or through
geophagia can potentially reduce the absorption of already bioavailable nutrients, particularly
micronutrients such as Fe, Cu and Zn. These in vitro findings, while disagreeing with the commonly held view of
geophagia as a source of nutrient supplementation, are consistent with
micronutrient deficiency problems observed in clinical nutrition studies conducted amongst geophagic populations. The work also showed that, in some cases, the ingested
soils may become a source of Ca, Mg and Mn, although it is not clear why other similar
soils should not release any of these
mineral nutrients.