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Did you know? – Geophagy, or soil for lunch

In some cultures around the world, eating soil is considered normal. In particular, people in parts of Africa, India and the USA regularly eat certain soils.

This is not as bizarre as it sounds. Soils contain minerals, and these minerals can supplement an insufficient supply in food. The practice of pica, defined in Western culture as an abnormal craving for non-food substances, becomes the practice of geophagy ("earth-eating") in other cultures. (Note, however, that pica is common in children, and where this occurs in situations where old lead-based paint has been stripped, lead poisoning and brain damage are possible.)

Traditional cultures cannot have known that soil contains essential minerals that may be lacking in the diet, nor that it contains clays that bind plant toxins. But trial and error would have shown that the ingestion of soil or certain clays would have made toxic plants edible (in situations where there was nothing else to eat), or would have kept people healthy.

Cation exchange ... again!

One of the key components of eaten soil is clay. Avid Fertile Minds readers will by now have twigged to the role of cation exchange in adsorbing some of the toxins in foods to the surfaces of the clay particles in the soil. The alkaloids and various other toxins found in many wild foods are highly bitter, to deter herbivores, and potentially lethal. In the acidic condition of the stomach, they become positively charged, which, as we have seen, draws them to the negative charge of the clay particles. This allows both non-technological peoples and various wild animals (notably parrots) to evade the plants' defence chemicals and benefit from the nutrients.

Medicinal earth

Have you ever taken a thick, evil-tasting liquid for diarrhoea or flatulence? It would have contained kaolin or attapulgite, both common clay minerals. That's right – you've eaten soil. The clays absorb both water and gases, reducing both problems.

Further reading

Geophagy. Wikipedia.

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