Adaptive function of soil consumption: anin vitrostudy modeling the human stomach and small intestine

Abstract

Despite occurring in a wide variety of taxa, deliberate soil consumption (geophagy) is a poorly understood behavior. In humans, geophagy is sometimes considered aberrant or a sign of metabolic dysfunction. However, geophagy is normally assigned an adaptive function in nonhuman primates and various other organisms. One hypothesis submits that clay-rich soil adsorbs intestinal insults, namely plant metabolites or diarrhoea-causing enterotoxins. Here we test the capacity of kaolin, a commonly ingested clay, to adsorb quinine (an alkaloid) and two types of tannin (digestion-inhibitors). Trials were conducted in vitro using the TNO Intestinal Model, a device that closely simulates digestion by the human stomach and small intestine. Kaolin reduced the bioavailability of each compound by ≤30%. However, because we could not replicate clay-epithelial adhesion and reduced motility, these results may underestimate adsorption in vivo. We also show that kaolin fails to render calcium oxalate soluble. We conclude that gastrointestinal adsorption is the most plausible function of human geophagy. Adaptive advantages include greater exploitation of marginal plant foods and reduced energetic costs of diarrhoea, factors that could account for the high frequency of geophagy in children and pregnant women across the tropics. Movies available on-line

The effect of kaolin feeding on efficiency, health status and course of diarrhoeal infections caused by enterotoxigenic Escherichia coli strains in weaned piglets

“…They can firmly and selectively bind harmful substances from feeds in the intestines and thus reduce their absorption across the intestinal mucosa and resulting toxic effect (Knezevic and Tadic, 1994;Phillips, 1999;Abdel-Wahhab et al, 1999;Hassen et al, 2003;Katsumata et al, 2003;Dominy et al, 2004). Bartko et al (1983) and Boranic (2000) emphasized the high selective ion exchange capacity of clay minerals.…”

“…Natural clay minerals improve the function of the intestinal barrier and are effective in treating gastroenteric diseases in humans and animals (Castro and Elias, 1978;Said et al, 1980;Vrzgula et al, 1982;Brouillard and Rateau, 1989;Ramu et al, 1997;Narkeviciute et al, 2002;Dominy et al, 2004;Castro, 2005). Their use retards the rate of digestive passage through the intestines and their ability to absorb water results in more compact and better shaped faeces.…”

“…has been investigated. The effect of these natural materials in the prevention of enteric diseases is above all based on their ability to absorb enterotoxins and significant mycotoxins (AbdelWahhab et al, 1999;Phillips, 1999;Boranic, 2000;Dominy et al, 2004;Trckova et al, 2004).…”

“…When kaolin is added to animal diets, it reduces resorption of harmful toxins present in the feed through intestinal mucosa to the organism because it binds them firmly and selectively, and thus eliminates their toxic effects. A number of studies have demonstrated the excellent ability of kaolin to decontaminate enterotoxins which cause diarrhoea (Dominy et al, 2004), aflatoxins (Schell et al, 1993;Abdel-Wahhab et al, 1999;Phillips, 1999), plant metabolites (alkaloids, tannins), pathogenic microorganisms, heavy metals (Hassen et al, 2003;Katsumata et al, 2003), and poisons (Knezevich and Tadic, 1994). Kaolin added to farm animal diets can also influence their efficiency and perhaps also quality of meat (Savory 1984;Sakata, 1986;Kolacz et al, 2005).…”

The role of vitamin E or clay in growing Japanese quail fed diets polluted by cadmium at various levels

“…Clay, given to the animals in the diet, firmly and selectively binds compounds present in the diets which are noxious to the intestine and thus decreases their absorption through intestinal mucosa into the organism and subsequently prevents their toxic mode of action (Phillips, 1999). A number of studies confirmed clay capability to decontaminate aflatoxins (Abdel-Wahhab et al, 1999) plant metabolites (alkaloids, tannins), diarrhea causing enterotoxins (Dominy et al, 2004) and heavy metals (Katsumata et al, 2003). The present study aimed to investigate the role of Vit E or natural clay on growth performance, carcass traits, some blood biochemical components and Cd residues in muscles and liver of growing Japanese quail fed diets polluted by Cd at various levels.…”