Sketchy "health" stores tend to sell jars of clay, and the cable channel "Animal Planet" was happy to advertise for them when their oddity show was talking about macaws. Macaws, unlike humans, actually have a digestive system designed for eating clay.
One of the more recent incarnations of geophagia, the Clay Cleanse Diet (CCD) is an alternative medicine fad diet that claims that ingesting clay can reduce weight and remove toxins and surfaced around 2014 as a potential weight loss method.
All of this is a terrible idea and you shouldn't do it.
That being said, there is a nugget of truth in geophagia as a detoxification method. It has been demonstrated that geophagia in association with potato eating, particularly the more toxic wild potatoes in times of famine, has a detoxification effect. Detoxification has also been suggested as an adaptive function in non-human primates but as not been shown experimentally. Geophagia is further linked to to plant domestication, at least in the case of potatoes.
CCD itself is probably effective at weight loss. The clay does expand in the stomach, and will make people feel significantly
more constipated less hungry. Users of the diet claim to have lost 10 pounds over 10 days. If you wish to lose weight with a quick time scale but comparable health risks, you might consider removing unnecessary limbs or deliberately losing blood.
As a cleanser clay removes
absolutely nothing "toxins" from the body by doing stuff. The users of this diet fail to present any scientific evidence that it removes "toxins" from the body, or what those toxins are, as is typical for "cleansing" claims. Kaolinite and montmorillonite clays have been shown to adsorb heavy metals in vitro, not in humans specifically.
CCD itself is not safe and should be avoided. It can potentially contain high levels of heavy metals, soil-based pathogens (nematodes and microbes), can block your colon, and can damage your stomach and intestines. Geophagia has been associated with hyperkalemia (excessive potassium in the blood), resulting in cardiac arrest and paralysis in five patients with chronic renal failure.
Pica is a condition characterized by an urge to eat soil (among other non-nutritive things, such as sand and utensils) due to chemical imbalance, neurological response to iron deficiency, etc. It is particularly common among small children, pregnant women, and those with developmental disabilities.
Basic sustenance in poverty
Poor (dirt-poor?) Haitians sometimes eat a yellow dirt with added salt and vegetable shortening because they cannot afford rice. This way starving to death is less of a painful experience, and takes a long enough time that someone might notice their plight.
Many animals eat dirt, primarily to get missing nutrients (especially salt). Confined farm animals are especially prone to geophagia, and goats are reported to suffer from gastro-intestinal lesions from geophagia.
- The Most Extreme — Ep 23 — Eaters. The… narrator… was… most… enthused…
- "A chemical-ecological model of root and tuber domestication in the Andes" by Timothy Johns. In: Foraging and Farming: The Evolution of Plant Exploitation, edited by David R. Harris & Gordon C. Hillman (2016) Routledge. ISBN 1138816019.
- Detoxification function of geophagy and domestication of the potato by Timothy Johns (1986). Journal of Chemical Ecology, vol. 12, no. 3., pp. 635-646.
- Cue hilarious SCARY Daily Mail headline. (Sorry about linking to the Daily Heil, but this is their specialty and no serious scientists seem to have wasted their time on this bit of woo so far.)
- Adsorption of a few heavy metals on natural and modified kaolinite and montmorillonite: A review by Krishna Gopal Bhattacharyyaa & Susmita Sen Guptab (Volume 140, Issue 2, 5 August 2008, Pages 114–131). Advances in Colloid and Interface Science doi:10.1016/j.cis.2007.12.008
- Geophagy and potential health implications: geohelminths, microbes and heavy metals by R. Kutalek et al. Trans R Soc Trop Med Hyg. 2010 Dec;104(12):787-95. doi: 10.1016/j.trstmh.2010.09.002.
- Geophagia: A Cause of Life-Threatening Hyperkalemia in Patients With Chronic Renal Failure by Michael C. Gelfand et al. JAMA. 1975;234(7):738-740. doi:10.1001/jama.1975.03260200054019.
- City of Sandersville, Georgia: Kaolin Capital of the World
- The Old And Mysterious Practice Of Eating Dirt, Revealed by Linda Chen (April 02, 201412:46 PM ET) National Public Radio.
- Poor Haitians Resort to Eating Dirt
- If You Can't Afford Rice In Haiti, You Eat Dirt
- Small ruminant research and development in Africa: Proceedings of the Second Biennial Conference of the African Small Ruminant Research Network. AICC, Arusha, Tanzania, 7-11 December 1992 (1994) p. 140. ISBN 929053284X.