Americans are expanding their repertoire of foods but confronting new medical problems along with it. The latest: pine mouth syndrome, a bitter, metallic taste in the mouth that can develop a day or two after eating pine nuts, an increasingly popular ingredient in pesto, salads and Italian dishes.
First described by a Belgian poison-control doctor in 2001, the rare syndrome can linger for up to two weeks. A recent article about it in the Journal of Medical Toxicology found dozens of anecdotal reports online.
Marc-David Munk, a professor in the Department of Emergency Medicine at the University of New Mexico in Albuquerque, was struck with the syndrome himself and describes it in the Toxicology paper.
"It's surprising to me that more people don't know about it," he says.
Although almost non-existent in the medical literature, the syndrome is certainly something people who have had it are aware of. In the past year, the Food and Drug Administration received 51 complaints of "taste disturbances" related to pine nuts. The agency hopes information from consumers and tests of pine nuts associated with this syndrome will help it determine what's causing the problem, says spokesman Michael Herndon. Because it's related only to taste, it's not considered a public health problem, he says.
It's known that pine nut oils become rancid very easily, so it's possible that as they degrade, they might form new molecules that somehow interact with the taste receptors, Munk says.
He experienced it firsthand at a buffet table at a restaurant where there was a bowl of pine nuts by the salad bar. "I just grabbed a handful of them and ate them raw. Within a couple of days, I developed metallogeusia" (meh-tal-ah-GOO-zee-ah).
That's the medical term for a bitter metal taste in the mouth. Munk found it was even stronger when he drank red wine. His case lasted 10 days.
Though there's no scientific proof that the metallogeusia is linked to pine nuts, dozens of reports online suggest it is. Whether they're raw or cooked doesn't seem to matter.
Munk believes something in the pine nuts affects the signaling between the taste buds and the brain. There are several well-known triggers for metallogeusia, including ingesting certain seafood toxins, zinc deficiency, strokes and, most commonly, taking ACE inhibitors for blood pressure, he says.
In the Belgian case, the doctor was able to reproduce the symptoms by feeding the implicated pine nuts to two other people.
Americans consumed 10.4 million pounds of pine nuts in 2008-2009, the last year for which figures are available. The overwhelming majority of pine nuts consumed in the United Sates come from China, according to the Department of Agriculture's Economic Research Service. According to the medical literature, a tiny proportion also come from Italy and Pakistan.
Costco, which because it is a membership organization can track exactly where a given batch of pine nuts came from, says it has had "two or three" reports of pine mouth from customers, spokesman Craig Wilson says.
The company took samples from the offending pine nuts and sent them and a control bag of pine nuts that didn't cause the symptoms off to nationally recognized labs.
"They were the same," Wilson says. "It's very strange." A full toxicological panel of tests revealed no differences.
"There are a lot of questions to be answered on this one," Munk says. But since his paper was published, he says, it has become clear that the condition is a real medical effect. In the past months, he has had "people e-mail me out of the blue to describe their symptoms."
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