Common Foods That You Didn't Know Can Be Toxic

There are a number of foods that, although generally healthy and packed with nutrients, can be toxic if an individual eats a particular part or prepares the food in a particular way. Most of these potentially dangerous foods are plant-based, including certain fruits, tubers, and legumes. As the World Health Organization (WHO) explains, in many cases, these naturally occurring toxins serve as a defense mechanism for the plant. These toxins don't harm the plant, but can cause issues for creatures (including humans) who eat the plant. Other toxins may be released by a plant when it's under stress.

Toxins from food can cause a variety of symptoms, ranging from mild nausea and GI upset to potentially life-threatening organ damage. Some of the most common natural food toxins include cyanogenic glycosides (compounds that can transform into cyanide once consumed), furocoumarins (a stress chemical released by certain plants), lectins (found in many types of beans), solanines and chaconine (found in potatoes, especially those exposed to light), and muscimol and muscarine (poisonous compounds found in some mushrooms).

To minimize your risk of getting sick from these toxins, don't automatically assume that all parts of a common food are safe to eat. Use caution when eating foods in their raw form, and discard foods that are heavily bruised, discolored, or damaged. Do not eat foods foraged in the wild unless they've been identified as safe by an expert. Here are some common foods that can actually be toxic.

Mushrooms

When you think of potentially toxic foods, mushrooms are probably the first thing that come to mind. However, if you're a fungus lover, the good news is that only about 3% of mushroom species are toxic (via the Cleveland Clinic). 

Mushroom toxicity can run the gamut from gastrointestinal upset to liver and kidney failure and even death. GI symptoms can appear within just 20 minutes of eating toxic mushrooms and include abdominal pain, nausea, vomiting, and diarrhea. These are usually relatively short-lived and pass once the mushroom has made its way out of the body. More dangerous types of mushrooms include those in the Amanita genus, such as the death cap mushroom. These mushrooms contain amatoxins, which damage liver cells. If an individual eats one of these mushrooms, they'll likely have initial GI symptoms, seem to recover for two or three days, and then suddenly become sick again. Amatoxin damage can lead to liver failure, kidney failure, internal bleeding, and, in the most severe cases, death.

There's currently no antidote for amatoxin poisoning, although silibinin, which is extracted from the milk thistle plant, may potentially block liver cells' ability to absorb the toxin. Currently, doctors can only provide supportive care, such as IV fluids, for people who've ingested poisonous mushrooms. Given how similar poisonous and nonpoisonous mushrooms can look, it's important to never eat foraged wild mushrooms unless they've been identified by an expert as safe. Toxic mushrooms don't necessarily taste bad, and cooking them doesn't remove the danger.

Cherries

Cyanide isn't just a tool used by assassins. The Centers for Disease Control and Prevention (CDC) explains that there are several routes through which a person can be exposed to this potentially lethal toxin, including breathing in cigarette smoke or smoke from a fire and eating certain foods. Cyanide prevents your cells from using oxygen, causing them to die. Exposure to a large amount of cyanide can be fatal within minutes to hours. Inhaling or ingesting a small amount of cyanide can cause dizziness, headache, nausea, vomiting, rapid heart rate and breathing, and weakness, while exposure to a large dose can result in low blood pressure, convulsions, loss of consciousness, and respiratory failure. There are antidotes for cyanide poisoning, but they must be administered quickly to be effective.

As the Canadian Food Inspection Agency states, the kernels within the pits of cherries and other stone fruits contain a substance called cyanogenic glycoside. Although not dangerous on its own, cyanogenic glycoside can transform into hydrogen cyanide, which is very dangerous to humans, when the kernels are chewed. Other stone fruits whose kernels contain cyanogenic glycoside include peaches, plums, and pears. This doesn't mean you need to give up these foods; simply avoid eating the pits. Cassava root (yuca) and bamboo shoots also contain cyanogenic glycoside, and should always be cooked before eating to neutralize the compound. The Food Inspection Agency noted that the lethal dose of cyanide ranges from 0.5 to 3.0 milligrams per kilogram of body weight.

Elderberries

As Medical News Today explains, the Sambucus tree produces fragrant white or cream-colored elderflowers and blue or black elderberries. In addition to being delicious, especially when turned into jam, baked into pies, juiced, or fermented into wine, elderberries have been used for centuries for their alleged health benefits. Elderberries contain significant amounts of vitamins A and C, potassium, folate, calcium, and iron. Research suggests that they may help fight off respiratory infections such as influenza and the common cold, and topical elderberry extracts may be helpful in managing acne and reducing the appearance of wrinkles.

According to the Centers for Disease Control and Prevention (CDC), however, this plant can also contains substances that, under certain conditions, can produce hydrocyanic acid, which is toxic. These compounds can be found throughout the plant, but are most concentrated in the roots, leaves, stems, and immature berries. Ingestion can cause symptoms such as nausea, vomiting, abdominal pain, weakness, dizziness, numbness, and stupor. Even ripe berries may produce nausea if eaten raw, so it's always best to cook elderberries. 

If pressing elderberries for juice or as the first step to making wine, ensure all stems and leaves have been removed. In the 1980s, 11 members of a religious group became sick within 15 minutes of drinking elderberry juice that had been pressed several days before and contained bits of leaves and stems. Eight of the individuals had to be flown to a medical center for treatment, although all recovered.

Potatoes

You've probably heard that eating green or sprouted potatoes can make you sick, but is there any truth to that, or is it just an old wives' tale? 

According to Poison Control, potatoes contain solanine and chaconine, two toxic substances known as glycoalkaloids. These "cause toxicity through cell disruption leading to gastrointestinal symptoms such as vomiting, abdominal pain, and diarrhea. Some people may also experience headache, flushing, confusion, and fever." Some people have even died from consuming large amounts of these toxic glycoalkaloids. Exposure to light increases both the chlorophyl and glycoalkaloid content of potatoes. The large amounts of chlorophyl turn the potato's skin green. While chlorophyl is harmless, a green potato means glycoalkaloid content is also elevated. The "eyes" and sprouts of a potato contain concentrated amounts of solanine and chaoconine. So it's best to toss green or sprouted potatoes.

But just how much of these glycoalkaloids can you eat before becoming sick? Per Smithsonian Magazine, "studies have recorded illnesses caused by a range of 30 to 50 mg of solanine per 100 grams of potato, but symptoms vary depending on the ratio of body weight of the toxin and the individual's tolerance of the alkaloid." Smithsonian Magazine notes that death from solanine poisoning is very rare today and commercially grown potatoes are screened for high glycoalkaloid content before being sold (though, as mentioned above, these toxins can build up naturally over time, especially when potatoes are exposed to light).

Kidney beans

Kidney beans are an extremely nutritious legume. They're packed with protein, fiber, and important micronutrients such as iron, folate, magnesium, and potassium (via Healthline). But eating raw or undercooked kidney beans can do more harm than good. That's because, as the Food Network explains, raw kidney beans contain extremely high levels of substances known as lectins, specifically one called phytohaemagglutinin. Lectins can cause clumping of red blood cells and interfere with absorption of nutrients from the GI tract. Although humans can tolerate tiny amounts of lectins, large quantities cause extreme nausea, vomiting, abdominal pain, and diarrhea one to three hours after ingestion. Fortunately, symptoms usually don't last long. In severe cases, hospitalization may be required.

Red kidney beans contain the largest amount of phytohaemagglutinin, measured in hemagglutinating units (hau). Raw red kidney beans contain 20,000–70,000 hau, while fully cooked beans contain just 200–400 hau. It's no surprise, then, that eating just a few raw kidney beans is enough to cause symptoms. By contrast, white kidney beans have only about a third of the phytohaemagglutinin as their red counterparts.

When preparing kidney beans, soak them overnight and then toss the soaking water. Cook the beans in fresh water and make sure they are maintained at boiling for at least 10 minutes. Use caution when cooking beans in a slow cooker, as they may end up being undercooked and still packed with lectins. Canned beans are completely safe, as they've already been thoroughly cooked.

Rhubarb

If you're at the grocery store or farmer's market looking for some rhubarb to add a bit of zip to pies, muffins, or other baked goods, you'll notice that these brightly colored stalks are always sold without their leaves. As Taste of Home explains, rhubarb stalks are perfectly safe to eat, even raw. The leaves, however, contain extremely high amounts of oxalic acid, and are considered toxic to humans and other animals. While accidentally consuming a small leaf scrap is unlikely to do any harm, eating just a few large leaves could leave you feeling a bit ill. You'd have to eat several pounds of leaves, however, to reach truly toxic levels.

According to A.D.A.M., rhubarb leaves also contain anthraquinone glycosides, which, along with the oxalic acid, may contribute to its toxic effects. Rhubarb poisoning can cause a variety of painful, and even potentially fatal, symptoms. These include blisters and pain in the mouth and throat, abdominal pain, increased salivation, vomiting, diarrhea, difficulty breathing and speaking, seizures, and coma. In addition to rhubarb leaves, oxalic acid is also found in caustic industrial substances such as metal cleaners, bleaches, and anti-rust products (via Mount Sinai Hospital).

The lethal dose of oxalic acid depends on the weight of the individual, and is estimated to range between 15 and 30 milligrams for adults. Still, you'd need to eat a lot of rhubarb leaves to ingest that much oxalic acid (via Compound Interest).

Cinnamon

Cinnamon is one of those rare foods that's both extremely healthy and delicious. According to WebMD, there are two types of this spice commonly sold in the United States: cassia and Ceylon (true) cinnamon. A number of studies (mostly in animals) suggest that cinnamon may help lower blood sugar and cholesterol levels in diabetic individuals. It may also assist with weight loss, irritable bowel syndrome (IBS), allergies, and infections. Cinnamon has both antioxidant and anti-inflammatory properties. The compound cinnamaldehyde is believed to be behind many of cinnamon's supposed health benefits.

But as Healthline explains, cassia cinnamon (the cheaper, more widely available form of the spice) contains high amounts of coumarin, a compound that could have adverse health effects when overconsumed. And you don't have to eat a lot of cinnamon to get too much coumarin: One teaspoon of ground cassia cinnamon contains 7-18 milligrams of coumarin. The tolerable upper intake limit (UL) for coumarin is 0.05 milligrams per pound of body weight, so the UL for a 130-pound woman would be only 6.5 milligrams. Excess consumption of coumarin has been linked to liver damage, mouth sores, and an increased risk for certain types of cancer.

The good news is that even though some groups of individuals may be more susceptible to the liver-damaging effects of coumarin, acute coumarin poisoning is "extremely rare" (via the McGill Office for Science and Society). Additionally, trace amounts of coumarin can also be found in green tea, carrots, and some beers.

Nutmeg

Nutmeg is another spice that has a dark side when consumed in excess. As WebMD explained, nutmeg comes from the seed of the Myristica fragrans tree, and is a popular addition to both sweet and savory dishes around the world. Besides its warm and ... well, nutty ... flavor, nutmeg offers a wide array of micronutrients. These include vitamins A, C, and E; minerals like copper, iron, zinc, and magnesium; and antioxidants that may guard against cancer, heart disease, and liver damage. Research indicates that nutmeg may improve sleep, boost mood, and offer some protection against pathogens. While nutmeg is perfectly safe when eaten in the quantities one would find in food, consuming even just two teaspoons (5 grams) of the stuff can have toxic effects.

According to a 2014 paper published in the Journal of Medical Toxicology, nutmeg's toxic effects can be attributed to two substances, myristicin and elemincin. Once ingested, myristicin is metabolized to a compound that can cause hallucinations, while eleminicin can decrease muscle activity and coordination. When consumed in large quantities, nutmeg can cause hallucinations, agitation, nausea and vomiting, drowsiness, and rapid heart rate. There have been at least two documented cases of individuals dying from nutmeg poisoning. Almost all cases of nutmeg toxicity, however, are the result of people — most often teens — intentionally consuming large quantities of nutmeg in order to get high. In many cases of nutmeg poisoning, individuals were also consuming other substances with psychoactive effects.

Mangoes

Is there anything more luscious than a ripe mango? While the flesh of this tropical fruit is safe to eat, individuals should exercise caution when handling and peeling mangoes. As Encyclopedia Britannica states, mangoes are part of the Anacardiaceae family of plants, which includes poison ivy, poison oak, and poison sumac. These plants contain an oily substance called urushiol that can produce a rash if it comes in contact with your skin (via Compound Interest). The urushiol in mangoes is found only in the peel, particularly around the stem. Bruising of the fruit can trigger the release of urushiol. 

If you're particularly sensitive to urushiol, just handling a mango could cause issues. For this reason, most mangoes sold in grocery stores are prewashed to remove as much urushiol as possible. It's still a good idea to wash mangoes in warm water with a scrub brush before peeling, though. Eating a bit of mango peel can cause a tingly, itchy rash around your mouth that can spread to the rest of your body (via Women's Health).

According to WebMD, it is possible to eat mango peels, and they do contain fiber and a wide variety of healthful micronutrients. Even with the urushiol removed, however, they can be unpleasant to eat raw. Still, you can make a syrup out of mango peels or dehydrate them. It's important to note, though, that in addition to urushiol, mango peels may contain high levels of pesticides. To play it safe, skip the peel altogether and go for the goodness inside.

Cashews

If you buy a bag of cashews labeled "raw," they're anything but. And that's a good thing because, as Healthline explains, truly raw cashews contain high levels of urushiol. Even if the cashews you buy look very natural and unprocessed, they've actually gone through a lengthy process to remove the urushiol. Once harvested, cashews, still in their shell, are often left to dry. Then they're subjected to very high heat, either by steaming them in a rotating drum or submerging them in a vat of boiling oil. Then they're shelled, dried again, and peeled. At this point, cashews are often packaged and erroneously labeled as "raw." In other cases, the cashews will be roasted a second time to enhance their taste, and other flavorings (such as honey) may be added.

While it's generally very safe to buy commercially produced cashews, accidents in processing do very occasionally occur. According to the Centers for Disease Control and Prevention (CDC), in April 1982, 54 people in Pennsylvania developed an urushiol-induced rash after eating cashews they'd purchased as part of a Little League fundraiser. The Little League organization had bought the cashews from a local company, who had imported the cashews from Mozambique but hadn't properly processed the nuts. Many of the bags of cashews contained fragments of urushiol-rich shell.

Never eat cashews directly off a tree and make sure that anyone who gives you homegrown cashews knows how to safely process them.

Lychee

Lychee is a delicious tropical fruit common in Asian cuisine. According to WebMD, lychee is packed with micronutrients, including large amounts of vitamin C and antioxidants that may prevent cancer, lower triglycerides, and reduce the risk of liver disease.

But lychee can be deadly if eaten when not fully ripe. As Psychology Today explained, for many years, India, Vietnam, and other places where lychee is grown would experience seasonal epidemics of sick children. At the same time each year, hundreds of children would fall ill with seizures and encephalopathy (a disruption in normal brain function). As many as 30%–40% of those who became ill died. Initially, epidemiologists suspected some type of infectious disease, but in 2015 authorities finally discovered the true culprit: unripe lychee. Unripe lychee naturally contain a substance called methylenecyclopropylglycine, which can decrease blood sugar to dangerously low levels (hypoglycemia), resulting in the neurological problems seen in the sick children.

In an interview with CNN, Dr. Padmini Srikantiah of the Centers for Disease Control and Prevention (CDC) office in India noted that small body size and general malnourishment made these children more susceptible to the methylenecyclopropylglycine in unripe lychee. She also explained that "it's quite possible that when glucose metabolism is disrupted, you get buildup of other metabolites that could have some toxic effects as well." Ackee fruit, a relative of the lychee grown in Jamaica and West Africa, contains similar toxins and should never be eaten unripe or uncooked.

Star fruit

Sometimes even ripe fruits can be toxic to some people or when eaten in excess. This is the case with star fruit. As a 2020 paper published in the Indian Journal of Nephrology explains, star fruit is a tropical fruit commonly eaten in countries such as India, Brazil, and Mexico. Like persimmons, it comes in two distinct types: a sweet variety and a more sour variety that's usually used to make juice. Both varieties contain two compounds that can be toxic if eaten in large quantities or if an individual has kidney disease and reduced renal function. The first is oxalic acid, which can lead to irritation of the digestive tract in sensitive individuals beginning minutes after consuming the fruit. Within a few hours, the oxalic acid can form crystals that block the renal tubules — the tiny tube-like structures in the kidneys that allow them to effectively filter the blood. Even if your kidneys are perfectly healthy, consuming a large amount of star fruit can lead to kidney damage.

The second potentially dangerous compound in star fruit is a neurotoxin called caramboxin. Healthy kidneys can easily process and remove this neurotoxin from the blood, but if an individual's kidney function is compromised, the neurotoxin can build up in the brain, causing a variety of symptoms. Mild symptoms include hiccups, vomiting, and insomnia, while moderate and severe symptoms include agitation, sudden numbness or tingling in the limbs, muscle weakness, seizures, coma, shock (dangerously low blood pressure), and even death.

Brazil nuts

Selenium is a trace mineral you've probably never heard of, but it's essential for good health. Per the National Institutes of Health (NIH), selenium is "a constituent of more than two dozen selenoproteins that play critical roles in reproduction, thyroid hormone metabolism, DNA synthesis, and protection from oxidative damage and infection." The recommended dietary allowance (RDA) has been set at 55 micrograms for adult men and non-pregnant women, 60 micrograms for pregnant women, and 70 micrograms for breastfeeding mothers. Brazil nuts are inordinately high in selenium — a single ounce contains 544 micrograms, almost 10 times the RDA. In fact, Brazil nuts contain more selenium than the upper tolerable intake level (UL), which is set at 400 micrograms for all adults.

According to the SF Gate, excess selenium can cause both acute and chronic toxicity. The first clue that you may have overdosed on selenium (a condition known as selenosis) is a garlic smell to your breath and a metallic taste in your mouth. Other signs include nail and hair loss or brittleness, neurological issues, and gastrointestinal problems like diarrhea and nausea. Individuals may also experience rashes, skin lesions, fatigue, and irritability. In the most severe cases, kidney damage, heart failure, and even death may occur.

Fortunately, selenium toxicity is rare, according to a 2006 paper published in the Medical Journal of Australia. But about half of all cases result in death, usually within 6 hours of ingesting the large amount of selenium.

Foods commonly contaminated with toxic substances

Some common foods are inherently safe to eat, but often come contaminated with substances that are toxic to humans. Perhaps the best-known example are the high levels of mercury found in certain fish. According to WebMD, the worst offenders are swordfish, shark, tilefish, king mackerel, orange roughy, bigeye tuna, marlin, and Chilean sea bass. The Environmental Protection Agency noted that exposure to mercury can cause a number of adverse effects. Methylmercury (the form found in fish) is a powerful neurotoxin that can lead to loss of peripheral vision, lack of coordination, pins-and-needles sensations in the limbs, problems with speech and hearing, and muscle weakness.

Brown rice, for instance, is often touted as a healthier alternative to white rice, yet it can contain much higher levels of arsenic than its more refined counterpart. A report released by the Food and Drug Administration (FDA) in 2016 found that brown rice contained 154 parts per billion (ppb) of arsenic, compared to 92 ppb in white rice. According to the World Health Organization (WHO), "long-term exposure to arsenic ... can cause cancer and skin lesions. It has also been associated with cardiovascular disease and diabetes."

Oysters are another commonly contaminated food. According to ScienceDirect, oysters contain an average of 9–11 different types of contaminants. These include natural substances that can be toxic (such as arsenic, mercury, and cadmium), as well as potentially dangerous manmade substances such as phthalates and polycyclic aromatic hydrocarbons (PAHs).