Healing Plants with Cyanide

Enlarge Image Image Gallery Herbs that contain cyanogenic glycosides include bitter almond, elderberry, eucalyptus, flaxseed, and wild cherry. G. Ford

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Apricots, bamboo shoots, cassava, corn, wild cherry, elderberries, flaxseed, and lima beans all share a surprising trait: they’re all sources of cyanide.

These plants, along with almost 2,000 more, contain phytochemicals called “cyanogenic glycosides.” Cyanogenic glycosides have a chemical structure that contains one carbon with a cyanide group linked to a sugar (“glyco” means sugar). During digestion, the cyanide group is released and forms hydrocyanic acid (HCN). HCN is toxic to humans in small amounts (0.5 to 3.5 mg per kg), but if this amount is eaten over time, it’s not necessarily dangerous. Healthy humans can safely eat some cyanogenic plants if their diet includes adequate complete protein, which provides sulfur amino acids that help detoxify the HCN.

Bamboo shoots contain the highest amount of cyanogenic glycosides, with up to 8,000 mg per kg. Pandas can eat bamboo because they’ve adapted to a diet high in HCN, but people shouldn’t eat bamboo shoots raw or in great quantities. Cassava root contains a smaller amount of cyanogenic glycosides than bamboo (240 to 890 mg per kg), but is responsible for the majority of cyanide poisonings because it’s eaten as a staple food in tropical countries.

The cyanide-food connection

Among the twenty-four leading food plants in the world, sixteen are cyanogenic. Why are so many food plants cyanogenic? Scientists speculate that cyanogenic glycosides deter animals from feasting too heavily on the plant. The surviving cyanogenic plants were then more available to prehistoric humans—provided that people could process the plants to release HCN before consumption. Humans developed grinding, rinsing, and cooking methods to do this, and because animals don’t do any such processing, many tasty but cyanogenic plants were eventually adopted into agriculture.

Later in human history, we began to breed varieties with lower cyanide contents. For example, wild lima beans are much higher in cyanogenic glycosides than the supermarket limas we eat today. Older cookbooks recommend that limas always be boiled well in an open pot—for one reason, to break down cyanogenic glycosides that were still present at higher levels in older varieties. Boiling removes the HCN, but leaves the glycoside sugar, making the beans sweeter as well as safer.

Potent herbs

Herbs that contain cyanogenic glycosides include bitter almond, elderberry, eucalyptus, flaxseed, and wild cherry. And there’s a relationship between these compounds and the plants’ healing properties.

For example, wild cherry is a traditional American remedy for coughs, while bitter almond is the traditional Chinese treatment. These two plants are both in the genus Prunus, along with sweet almond, peach, plum, other cherries, and apricot. Prunus species contain the cyanogenic glycosides amygdalin and prunasin, which form HCN when digested. HCN tranquilizes our respiratory “cough center,” so amygdalin and prunasin may be responsible for wild cherry and bitter almond’s abilities to aid hacking coughs.

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