Pica in Humans: Remember Dr Joel Wallach from ‘Dead Doctors Don’t Lie’?

Recordings of the now infamous ‘Dead Doctors Don’t Lie’ cassette tape can still be found on the internet. When it was released in the 1990’s it caused quite a stir in the nutrition world. Wallach, a veterinarian by training, highlighted the conditions linked to mineral deficiencies in humans by using his past experience of treating farmyard and zoo animals with mineral supplements. In the tapes, Wallach talked about cribbing, a condition whereby mineral deficient stable animals will eat their bunks in order to satisfy their requirement for minerals. This occurs because of the instinctive tendency of animals to eat inorganic matter to provide a source of essential minerals. Certain animals for example will eat clay or soil for this reason (geophagia). A similar condition is known to occur in humans and is referred to as pica. Pica is the most common eating disorder in institutionalised mental patients, but interestingly the frequency of its occurrence in mental institutions is similar to that reported in some free living healthy populations.

In humans deficiencies of the minerals iron and zinc are most often associated with the development of pica (although others have been reported). For example, in one study1, researchers investigated the mineral status of 66 mentally retarded patients through analysis of hair and serum levels of minerals, 60 of the patients having been diagnosed with pica. The mineral status of the 6 non-pica diagnosed patients were all within the normal expected ranges. However, the patients with pica had low plasma levels of zinc and elevated plasma copper. Male subjects with pica also had significantly lower levels of serum iron. Plasma magnesium was borderline low in all 66 patients. The degree of zinc deficiency in the patients was associated with the severity of their pica, and in turn serum zinc was positively associated with serum iron and negatively associated with serum copper. However, the intakes of minerals from food did not correlate with the mineral statuses of the patients.

Therefore the authors concluded that the mineral deficiencies were as a result of poor mineral absorption. Some have suggested that it is the eating of inorganic foods such as clay and soil that is the cause of pica, rather than the result, based on the ability of clay to bind minerals in the gut. However, the fact that animals are able to select inorganic foods that contain the minerals they require by instinct, as demonstrated in animal feeding studies, would tend to suggest that the same is true in humans. Suggestions that the mentally retarded cannot discriminate between food and non food items were also dismissed by the authors as in some cases the patients were aggressive and determined in their efforts to locate and consume particular non food items. Interestingly the authors also noted that few of the subject with pica were undergoing any nutritional therapy for their condition. It is also interesting that supplements of zinc and iron were not given to the patients in order to see if this reduced the symptoms of their pica.

Dr Robert Barrington’s Nutritional Recommendation: Pica is common amongst pregnant women. This is likely because the mineral requirement of the foetus pulls minerals from the mother and causes her to become mineral deficient. To what extent pica is present in the general population is not known, and little research has been performed to investigate this phenomenon. Taking a multivitamin and mineral formula is the best way to guard against the development of the mineral deficiencies that may be the cause of pica. The elevated serum levels of copper with low serum levels of zinc in patients with pica are supportive of the suggestion that competition for absorption between the two minerals occurs in the gut.


1Danford, D. E., Smith, J. and Huber, A. M. 1982. Pica and mineral status in the mentally retarded. American Journal of Clinical Nutrition. 35: 958-967

About Robert Barrington

Robert Barrington is a writer, nutritionist, lecturer and philosopher.
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