Between 30 and 80% of people in Africa, especially women, regularly eat clayey soil - this habit is known as geophagy. They consume between 100 and 400 g per day. "Pregnant and breast-feeding women, in particular, nearly always have some soil to eat.

This is cheap to buy in the marketplace," explains Ruth Kutalek of MedUni Vienna's Center for Public Health (Institute of Social Medicine). The reason behind this habit, which was previously also widespread in Europe and Asia, is still not clear and is largely unresearched. A study conducted at MedUni Vienna has now been able to show that it is a craving.

That is the central finding of the paper that has now appeared in the renowned periodical "The American Journal of Tropical Medicine and Hygiene" and which arose from the dissertations of the three medical students Lena Hubl, Stephan Leick and Lukas Guttl under the supervision of Kutalek at the Center for Public Health. This paper describes soil-eating as a craving. The authors regard it as being similar to a craving for chocolate or as a type of "reward".

"These people often eat clay as a snack between meals and report that they could not do without it," added Kutalek

Detoxifying effect
However, the reason behind it could be quite different - and also quite multi-layered: Soil contains clay, which binds toxins, in the same way as charcoal tablets combat diarrhoea.

This clay could influence the pH of the stomach acid and help to combat heartburn - many women in Africa predominantly eat maize, cassava and pulses - but, as Kutalek explains, there are also indications that the soil helps with morning sickness.

Many African ethnic groups therefore regard soil-eating as "womanly" and the increased consumption of soil is seen as a sign that a woman is pregnant. However, according to the MedUni Vienna experts, men are also starting to eat soil more frequently, especially since clay is also regarded as a natural stimulant.

Reducing soil consumption is recommended
However, from a public health perspective, eating soil is questionable - at least in large quantities. Because, especially in Africa, soil contains a lot of heavy metals such as lead or mercury, which could be particularly harmful to unborn babies but also to their mothers and other adults.

"It is therefore strongly recommended that consumption be reduced," says Kutalek. The recommendation to stop completely is difficult to implement, because addictive behaviour cannot be changed overnight. MedUni Vienna's Center for Public Health is already conducting further research into the craving for soil.

Incidentally, some migrants from Africa who have come to Europe, and even Vienna, are in the habit of eating soil. It can be bought in portions in exotic supermarkets. And even health food stores offer bentonite clay for internal use. However, it is not advisable to consume this clay.