biology zoology blog benno meyer rochow on geophagy

On Geophagy

Biting the Dust to Live!

In 1961, Dr. Ananda S. Prasad described that some Iranian peasants near Shiraz were habitually engaging in geophagy, which means that they were voluntarily and purposefully ingesting clay. In Africa the consumption of termite soil is widely practiced as according to the Dutch entomologist Dr. Van Huis it is considered to be a carrier of medicines and therefore health-promoting.

Later Dr. Prasad received a medal for his discovery. I noticed in Jamaica that some dogs were regularly eating mud. Although I know I won’t get a medal for that observation, I wonder whether there could be a common reason for these behaviours in two quite different species of mammals? Let’s examine.

It was suggested to me by locals that dogs eat mud when they have worms, but I have my (unsubstantiated) doubts and am inclined to think that dogs are more likely to obtain worms rather than lose them by eating mud. Most likely, a lack of trace elements such as iron or zinc (as it had been shown to be in the Iranian case) and a craving for salt, which can lead to peculiar and unusual behaviours, were involved. An appetite for salt is particularly great in grass-eating animals as their food is deficient in this mineral and wild deer, mountain sheep, and antelopes are known to cover huge distances to frequent special so-called “salt-licks”. Making salt available in the form of salt blocks to domestic cattle and horses is common practice and “salt-licks” for pets are now even available in pet shops. Salt, after all, is an essential component of the body fluids and required for normal neuronal function. If the salt level falls below a certain level the animal is in trouble and will likely die

During times of reproductive stress or fluid losses with a disease, injury and sweating, body salt concentrations can be under threat, which is why presumably a specific appetite for salt has evolved in animals and humans (especially pregnant ladies). However, we know quite unambiguously from epidemiological studies especially in Finland where substituting potassium and magnesium for ordinary cooking salts (i.e., NaCl), that a too much of ordinary salt can affect the kidneys negatively and can cause high blood pressure and strokes so that a specific salt-seeking-instinct seems counterproductive (not to say maladaptive). Therefore, why this urge to ingest salt? Basic instincts indeed.

There is certainly no concern with the metabolic consequences when we take salt to satisfy our instinctive urge, just like the sexual activity in humans is rarely specifically aimed towards reproduction. The goal is the gratification of a desire and this is what can lead humans and animals to eat clay or mud. And to even more than that, as Mahatma Gandhi, who has been described by the celebrated British scientist Prof. J.S.B. Haldane as “a man, who knew a great deal more physiology than the Viceroy”, has demonstrated with the famous salt march of 1930: it ultimately led to India’s INDEPENDENCE!

© Dr V.B. Meyer-Rochow and, 2019.
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