Humans have evolved as hunter-gatherers, and a close contact with mother earth ensured a regular consumption of soil/dirt from uncleaned foods (e.g., vegetables with clinging soil), dirty hands, “unprocessed” water, etc. Some cultures have even been known to consume plain nonfood substances such as earth, chalk and sand on a regular basis, a behaviour referred to as “Pica”.
Pica has been documented through history, and a newer study in the northeastern Madagascar found that 63 percent of adult males engage in either Pica or amylophagy (the consumption of raw starches). The year prior to this study, another collection of data in the Madagascar region found that more than 50% of the sample group engaged in geophagy, the consumption of specific types of earth (1). Although the prevalence of Pica in Madagascar is uncommonly high, several other cultures have been known to eat various nonfood substances such as soil on a regular basis.
One teaspoon of soil contains billions of microorganisms from hundreds of different species. Although some of these microbes could be pathogenic, healthy soil also contains species of Clostridium and Bacillus that potentially boost our health. From an evolutionary perspective it seems very unlikely that soil bacteria are an important cause of disease, and it seems that contact with bacteria from a very young age (e.g., licking fingers, “dirty” foods) promotes a healthy microbiome (2).
While most people won’t start collecting and eating nonfood substances like earth and sand, strategies such as buying some “dirty” vegetables from the farmers market, doing some gardening, and avoiding the use of harsh cleaning products will ensure some exposure to soil microbes!
Recommended reading on the subject:
Eating of Soil and Raw Starch Documented in Madagascar
Dirtying Up Our Diets
Soil organisms: Bacillus Subtilis
Paleolithic microbiome in the modern world
PLoS One. 2012;7(10):e47129. doi: 10.1371/journal.pone.0047129. Epub 2012 Oct 17.
2. McDade, T.W., Rutherford J. , Adair, L, et al. Early origins of inflammation: microbial exposures in infancy predict lower levels of C-reactive protein in adulthood
Published online before print December 9, 2009, doi: 10.1098/rspb.2009.1795