Bentonite clay

What is bentonite clay?

Bentonite is a clay formed from weathered volcanic ash. Its main mineral is montmorillonite, an aluminum and magnesium silicate with a layered structure that can bind water and some other molecules. That binding property is why it is sold as a “detox” ingredient, and why some purified clays are used as anti-diarrheal medicines in other countries.

What the research says

The best human evidence comes from a purified pharmaceutical form called beidellitic montmorillonite. In a 2005 multicenter, double-blind trial of 524 people with IBS, 3 g three times a day for eight weeks did not significantly beat placebo in the overall group (51.7% vs 45.2% success). In the constipation-predominant subgroup, however, abdominal pain or discomfort improved in 49.4% versus 31.5% on placebo. Stool frequency did not change. Tolerance was good. This was a regulated drug product at a specific dose, not a supplement.

Lab and animal studies show clays can adsorb toxins, fats and microbes in the gut, but we found no rigorous human evidence that bentonite in a dietary supplement “cleanses” the intestines, removes parasites or improves regularity. Claims that it does are marketing, not established science.

Contamination is a real concern. Researchers at the National Institute of Environmental Health Sciences reported in a 2020 study that samples of a therapeutic “healing clay” contained high concentrations of arsenic and lead. Because clays come from the ground, their heavy metal content depends heavily on the source and on testing.

How it’s used in supplements

Bentonite appears in digestive capsules in undisclosed amounts, usually alongside fibers. Because clay can bind other substances, it may also reduce the absorption of medicines and nutrients taken at the same time. If a product contains bentonite, look for independent heavy-metal testing (a certificate of analysis), take it apart from any medication, and skip it during pregnancy, while breastfeeding and for children unless a doctor advises otherwise.

It is also worth separating bentonite from the claims made around it. “Detox” marketing often says clay pulls toxins, heavy metals or parasites out of the gut. The body already clears waste through the liver, kidneys and bowel, and we found no controlled human trials showing that an oral clay supplement improves those processes in healthy people. Most of the mechanistic support comes from laboratory and animal work, which cannot tell us what a few hundred milligrams in a capsule will do in a person.

Finally, note that the IBS trial used a pharmaceutical product manufactured to drug standards, with a defined mineral composition. Bentonite sold as a supplement ingredient can vary in mineral type, purity and contaminant levels from one source to the next. Without a published certificate of analysis, a consumer has no way to know which kind is in the bottle.