DEAR DOCTORS: I read that New York recently banned something called activated charcoal from all food and beverages. What is that, and why on Earth would anyone ever want to ingest it?

DEAR READER: The history of food fads is as long as it is strange. Back in the 11th century, after William the Conqueror successfully led the Norman conquest of England, he tried to conquer a weight problem with a liquid diet consisting mainly of alcohol. Lord Byron, the British poet and politician, was so enamored of vinegar as a curative that he made it the cornerstone of his diet and sparked a widespread fad.

In the 1830s, Americans were urged to eat a bland diet anchored by graham crackers to cool their sex drives. And in the Victorian era, women downed pills that supposedly contained a tapeworm egg (they probably didn’t) so the parasite growing in their intestines would take care of any excess calories.

Now comes activated charcoal, the latest in a centurieslong preoccupation with magical thinking about food. The substance is made by heating carbon-rich materials like wood, peat or coconut shells to extremely high temperatures. The resulting charcoal is then ground up and stripped of extraneous molecules, which creates ultra-fine particles full of holes and crevices. These increase the surface area of each minute particle, which makes available thousands of potential binding sites. Thus “activated,” the charcoal can now attract molecules, ions or atoms, making it a highly effective purifier. Activated charcoal is used in water filtration, and it is a go-to treatment in many cases of overdose and poisoning.

When added to food — the coconut variety is most widely used in this instance — activated charcoal transforms the familiar color palette of white, beige and brown to a startling dark black. From ice cream, smoothies and sauces to burger buns, beverages and pizza crust, an ever-growing range of everyday edibles is getting the activated charcoal treatment.

To be fair, much of the current rage for charcoal-infused foods arises from their visual shock value. But due to its ability to absorb impurities, activated charcoal has been assigned a wide range of health benefits, not all of them accurate. Some animal studies have suggested that activated charcoal may reduce certain damage associated with chronic kidney disease. There is evidence that it can ease intestinal gas, though the mechanism remains unclear. Claims that activated charcoal will clear the body of toxins or decrease bad breath remain unproven.

It can present some dangers as well. The same absorbent properties that make activated charcoal effective for poison control can also interfere with the absorption of medications. It can also cause constipation.

Still, it’s easy to understand how this latest food fad took hold. It’s also not surprising that it has become a target for regulation. Last spring, the Department of Health in New York City banned the use of activated charcoal in commercial food and drink. Health officials in San Francisco are also looking into addressing the trend. Advocates of activated charcoal have pledged to push back. It will be interesting to see what happens next.

– Eve Glazier, M.D., MBA, is an internist and associate professor of medicine at UCLA Health. Elizabeth Ko, M.D., is an internist and assistant professor of medicine at UCLA Health.

– Send your questions to askthedoctors@mednet.ucla.edu, or write: Ask the Doctors, c/o UCLA Health Sciences Media Relations, 10880 Wilshire Blvd., Suite 1450, Los Angeles, CA, 90024.

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