Naturally Dangerous: 11 Foods to Fear

Grown primarily in South America, Africa, and parts of Asia, this woody shrub is the third largest source of carbohydrates in tropical countries and a diet staple for more than half a billion people worldwide. Cassava roots and leaves contain toxic levels of two cyanogenic glucosides, linamarin and lotaustralin. Eating just a few pieces of a fresh cassava root can be lethal. Consumption of improperly prepared cassava has been linked to goiters, pancreatitis, ataxia, and a neurologic disorder known as konzo.

To reduce the cyanide content in cassava, the roots are peeled, cut into small pieces, and soaked and boiled in water. Processed cassava flour, which is used to make tapioca, has a very low cyanide content and is considered safe to eat.

Lychee trees and fruit are native to provinces of China but are also cultivated in India, Southeast Asia, and South Africa. Lychee seeds contain hypoglycin A and methylenecyclopropylglycine, two naturally occurring toxins found in soapberry fruits. In persons who are malnourished, the ingestion of unripe lychee fruit may cause severe hypoglycemia (≤ 70 mg/dL), metabolic derangement, fever, and brain dysfunction.

In 2013, the US Centers for Disease Control and Prevention (CDC) investigated outbreaks of unexplained neurologic illness in Muzaffarpur, India. Further investigation was conducted in the area’s large lychee-farming region, and a report was published in Lancet Global Health in 2017. The authors of the paper established an association between lychee consumption and the onset of hypoglycemic encephalopathy. Of the 390 children meeting the case definition who were admitted to two hospitals in Muzaffarpur, 122 (31%) died.

Almonds come in two varieties, bitter and sweet. Bitter almonds are broader and shorter than sweet almonds, and both contain amygdalin (the precursor of hydrogen cyanide). Levels of hydrogen cyanide are 40 times higher in bitter almonds, however. (Sweet almonds have a trace amount.) Even in small doses, raw bitter almonds are highly toxic and must be heat-treated to remove the poisonous cyanide.

In the United States, sweet almond is the only variety produced, and California is the only state that produces them—82% of the world’s supply. After two salmonella outbreaks traced to sweet almonds in the early 2000s, bulk sale of unpasteurized raw almonds became illegal in the United States, Canada, and Mexico. If not pasteurized by steam or heat, they are treated with a chemical, propylene oxide.

Were you aware that cashews labeled “raw” are not truly raw, and that they are actually seeds and not nuts? Cashews are slightly steamed to remove the toxin urushiol (found in their shells), the same chemical compound found in poison ivy.

People who are allergic or highly sensitive to poison ivy can have a fatal reaction if they are exposed to or ingest raw cashews. In April 1982, cashews imported from Mozambique and sold by a Little League organization in Pennsylvania caused a large outbreak of dermatitis and led to an investigation by the CDC. Several bags of cashews contained pieces of cashew shell.

Those who harvest cashews or work in cashew processing plants tend to exhibit greater allergy to cashew shells over time, with a high incidence of skin rashes and dermatitis (intense pruritus and redness; in severe cases, papules, vesicles, and bullae will appear).

Mangoes are cultivated in tropical climates. Almost half of the world’s supply is grown in India; China is the second-largest producer of the fruit. Mango leaves, stems, sap, and peels contain urushiol, the same toxin found in poison ivy and raw cashews. Physical contact with the fruit oils can cause swelling of the lips, dermatitis, and anaphylaxis in hypersensitive individuals.

Castor oil is widely promoted as a natural remedy for a variety of skin and hair conditions. It is commonly used as a laxative and added to many modern medicines. In the food industry, the oil is used as both an additive (including as a flavoring in candies and chocolates) and a mold inhibitor.

The vegetable oil is obtained by pressing the seeds of the castor oil plant (Ricinus communis). These seeds contain ricin, one of the most poisonous naturally occurring substances in the world. A single milligram of ricin can kill a human adult, and the accidental ingestion of a single castor seed can kill a child. Workers harvesting the seeds are required to follow strict safety guidelines to prevent accidental death and severe side effects, and production is limited in the United States. Heating during the oil extraction process denatures and deactivates ricin.

Predominantly cultivated in Indonesia, Malaysia, and Grenada, nutmeg is a fragrant spice commonly used to flavor a variety of baked goods, meats, sauces, and holiday beverages (such as eggnog). Raw nutmeg contains myristicin and elemicin, two phenylpropene compounds with psychoactive and anticholinergic-like effects.

Myristicin is a toxin, and the excessive consumption of raw nutmeg can result in poisoning. There have been numerous reports of intentional abuse of nutmeg by adolescents who combine it with other drugs. Consuming one to three whole nutmegs (or 5-15 g grated) can cause acute poisoning within 3-6 hours, with the onset of giddiness, hallucinations, and “nutmeg psychosis.” It can also induce palpitations, generalized body pain, and convulsions, and may lead to death. Symptoms may last for several days.

Potatoes are the fourth most-consumed food crop worldwide and a staple in many countries. China produces 25% of the world’s supply, followed by Russia, India, and the United States.

Glycoalkaloids (solanine and chaconine) are the toxic compounds found in the leaves, stems, sprouts, and tubers of potatoes. Exposure to light, physical damage, and age significantly increase the glycoalkaloid content (from 12-20 mg/kg to 1500-2000 mg/kg) and cause a greenish tinge to appear on the potato. With the increased consumption of commercial products such as french fries and potato chips, there is a growing food safety concern over potatoes used for processing.

Ingesting potatoes with high glycoalkaloid levels can lead to cramping, vomiting, diarrhea, confusion, headaches, neurologic problems, and even death in cases of acute toxicity. The lethal dose is estimated at 3-6 mg/kg of body weight.

Japanese star anise (Illicium anisatum) should not be confused with Chinese star anise (Illicium verum). The Chinese version is a popular spice used in many cultures. The Japanese version, on the other hand, contains anisatin, a highly toxic compound that can cause severe neurologic and gastrointestinal ailments such as diarrhea, vomiting, seizures, rapid eye movements, and respiratory paralysis.

In September 2003, the FDA issued an advisory to consumers to not drink teas brewed from either version of star anise until they are able to differentiate between the Japanese and Chinese versions.

The top two deadliest mushroom varieties are the “death cap” (Amanita phalloides) and the “destroying angel” (Amanita ocreata). The primary toxic compound is alpha-amanitin, considered the most lethal of all amatoxins found in the Amanita genus of mushrooms.

Symptoms within 6-12 hours of ingestion include severe abdominal pain, vomiting, and bloody diarrhea (causing severe dehydration, intense thirst, and a decrease in urinary output). Liver and kidney failure, as well as injury to the central nervous system, occur soon after. In more than half of cases of poisoning, the condition leads to coma and death.

In 2016, the California Poison Control System reported more than 670 cases of hazardous wild mushroom ingestion statewide in California within a year. A possible antidote derived from milk thistle, intravenous silibinin, is approved in Europe and is currently undergoing clinical trial investigation in the United States.