In Food Science, Dave McCowan from the University Of Chicago’s Department Of Physics answers our confounding questions about the mysterious world of food.
Before early humans began to domesticate plants for food, they foraged the wild for fruits, roots, and nuts. Through this process of discovery, it’s likely that one of our ancestors stumbled upon an almond tree and, despite finding the first few bites to be bitter, chowed down a handful of seeds. He then promptly died.
This unlucky fellow served as a lesson to his fellow gatherers that it isn’t only animals that defend themselves from attack. Nature gives us many plants that have evolved to produce pesticides, off-putting tastes, and—in extreme cases—lethal poison. Such protections ensure that the meanest plants survive to reproduce another day, and some of this toxic produce remains a part of our diet today.
The culprit in the almonds that did in our Neanderthal forbearer is a chemical called amygdalin, which, when metabolized by our bodies, produces cyanide. This nasty toxin interferes with the body’s ability to use oxygen and—even in small doses—can lead to nausea, headaches, muscle pain, and falling blood pressure. Cyanide, however, is more famous for its unambiguous effect in larger doses: quick death by suffocation. The Nazis used hydrogen cyanide (under the commercial name Zyklon B) in their gas chambers, the Jonestown cult committed mass suicide via potassium-cyanide-laced Kool-Aid, and Cold War spies were given cyanide pills they could bite down on to take their own lives, thus avoiding torture and interrogation at the hands of the enemy.
But back to that fatal almond. Today folks eat the nuts by the bagful without dying, so what gives?
Modern almonds are neither bitter nor full of amygdalin, and they represent one of humanity’s earliest domestication successes. As ancient gatherers learned to associate bitter tastes with danger, their palates led them to seek out sweeter (and safer) foods. Bitter almonds would have dominated what was found in the wild, but it is hypothesized that genetically mutated trees occasionally produced non-bitter, toxin-free nuts. Animals would eat these nuts, thereby destroying any chance for the sweet almond variety to propagate, but humans recognized the potential and began to harvest and plant exclusively those seeds. By as early as 3000-2000 B.C., domesticated almonds were common in several civilizations around the Mediterranean and Middle East. Wild bitter almonds can still be found at specialty shops, but need to be treated (not an easy task) to remove their poisoning potential.
Almonds aren’t the only amygdalin carrier, though. The toxic precursor is also present in apple seeds, cherry pits, and the kernels of stone fruits like plums, peaches, and apricots. Given the hardness of seed shells, the poison is typically released only by grinding up or thoroughly chewing the seed, and accidental deaths by this route are rare.
Still, toxicity levels can be alarmingly high. To suffer a lethal dose from apple seeds, you’d need to eat 200 of them (about 25 whole cores), but apricot kernels are so potent that as little as a single large seed can exceed accepted cyanide ingestion levels. Soaking cherry pits or peach kernels in alcohol to make infusions (or attempting your own homemade amaretto liqueur) can concentrate the amygdalin even further.
Cyanide poisoning isn’t the only way your pantry is fighting back, though. Another rich source of poison in plain sight is the nightshade family, a collection of plants rich in alkaloids that serve (depending on the dosage) as both neurotoxins, like nicotine and cocaine, and antidotes, like atropine (used to counteract nerve agents like VX and sarin) or scopolamine (used to fight motion sickness).
The deadliest nightshade is belladonna, which, though not cultivated for food, is a common flowering plant that grows across North America and Europe. Roots and leaves were used to make poison-tipped arrows in early civilizations, and Macbeth (yes that Macbeth) used a belladonna-derivative to dispatch his enemies. Today accidental poisonings occur when unsuspecting children eat the attractive red berries that, in an unusual twist for a toxin-producer, skew sweet rather than bitter.
As for edible varieties, the nightshade family includes such disparate foods as potatoes, tomatoes, eggplant, paprika, and even chili peppers. Several species include trace amounts of nicotine (though far less than is found in tobacco), and all varieties of peppers contain capsaicin, the chemical that makes spicy food taste “hot.” Although the effects of capsaicin in moderate doses are well known (irritation of the tongue and eyes, tingling sensation on the skin, sweating and increased saliva production), high doses can lead to swelling of the throat, thereby prohibiting breathing, or the brain. The amount needed to reach dangerous levels, however, is essentially unreachable in adults. Involuntary reactions to flush the toxin—i.e., puking it out—would probably take over before anyone could eat two dozen whole ghost peppers. (Deaths in children, however, have been reported.)
A more readily available nightshade toxin, however, is solanine. Found predominantly in potatoes (and perhaps in tomatoes as well), it is produced by the plant to ward off insects and hungry animals who might dig it up from the ground. Like capsaicin, it causes gastrointestinal distress as the body attempts to flush it from the system, but solanine works primarily as a neurological agent, inducing headaches, convulsions, or paralysis. The most famous incident happened in 1979 and involved nearly 80 British school children, some of whom slipped into comas, experienced seizures, or endured hallucination for several days after being fed year-old potatoes found in storage. (All of them fully recovered.)
In a fresh, healthy potato, the amount of solanine is nearly negligible. But when the tuber is exposed to light or damaged, its defense mechanism kicks in and production increases. Concentrations are highest in the sprouts that form on potatoes that have been sitting on the counter for a long time (so remove them) and in the skins of potatoes left long enough to go green (toss them). Boiling, frying, and otherwise cooking the potatoes do not appreciably reduce solanine levels, so suspect spuds should not be salvaged.
So, is the answer to swear off food forever? Hardly. But nature’s list of plants that bite back is long and their poisonous reach can be deadly. Relax and pass the cashews... no, the rhubarb… maybe the nutmeg… how about the cinnamon... You know what, I’ll just have saltines and water.