Do You Know Which of These Items Are Inedible?

By: Maria Trimarchi
Image: shutterstock

About This Quiz

From the color of potatoes to how much, exactly, is too much kale, see how your knowledge of edible versus inedible foods stacks up!

If you're like the average American who eats just a little more than 11 pounds of bananas over the course of a single year, have you ever wondered if you can eat the peel -- and if you try it, will it kill you? The skin is slightly bitter, and it's so fibrous it could stymie even a powerful jaw or blender. While there isn't a lot of scientific evidence to back up eating it, it won't hurt you. But consider this: Even monkeys peel before eating.

So what makes something edible, anyway -- does it just come down to if it tastes good or bad? It boils down to just two things, actually. One, your body has to be able to break it down and digest it. And two, it can't be toxic to humans. Toxins in some foods are naturally occurring, although in other instances and foods those toxins may form during processing or handling. Some toxins, for instance, will interfere with your nervous system, and can cause everything from mild symptoms such as nausea to seizures or even death. For the average American, though, toxic reactions to foods are relatively rare -- much less common than instances of, for example, food poisoning from salmonella, listeria or toxoplasma.

Feeling confident about your knowledge of what's safe and not safe to chow down on, whether it's store-bought, found at the farmers market, or from an afternoon of foraging? See how much you know about pits, seeds and plants -- some that we commonly consume -- that can poison, or even kill, us.

You would need to consume about 200 of which seeds to receive a fatal dose of cyanide?

It takes a dose of about 1 milligram of cyanide per kilogram of body weight for cyanide to reach fatal levels. That's chewing and eating about 200 apple seeds, or about 20 apple cores.

Sassafras, which contains the toxic compound safrole, used to be used to flavor what drink?

Before it was banned for use in food by the FDA in 1960 safrole-containing sassafras has traditionally been the primary ingredient in root beer -- both the soda and candy. Today, root beer is a combination of flavors, including sarsaparilla, cinnamon, clove, licorice, vanilla and wintergreen to name a few.

When it's green, which starchy tuber contains a compound that can cause gastrointestinal distress, confusion, or even death?

Red, purple and yellow potatoes aren't toxic, but don't eat green potatoes -- those are. The green is caused by chlorophyll, which, itself, is harmless. But green potatoes also contain high amounts of a naturally occurring chemical called alkaloid solanine, which can cause nausea, confusion and, in some cases, death.

Which common kitchen spice is also a hallucinogenic that may also lead to psychosis?

Nutmeg, an essential component to a classic béchamel sauce as well as the sprinkle on top of your eggnog, is actually a halluncinogenic -- but that depends on how much you eat. For instance, eating 0.3 ounces of nutmeg can lead to seizures -- but that's a lot of nutmeg. The amount of psychoactive neurotoxin, called myristicin, you consume when eating a whole seed can lead to "nutmeg psychosis," with symptoms including disorientation, hallucinations and hyperexcitability.

The pits of which fruits contain the poison cyanide?

While the fruit of apricots, peaches, plums and other stone fruits is sweet and, most importantly, not going to kill you, the pits (and leaves, too) of stone fruits contain a compound called amygdalin, which is made up of sugar and cyanide. Cyanide is known to be highly toxic to humans -- which leads to tissue damage and asphyxiation.

The leaves of which perennial contain oxalates?

Kale, rhubarb leaves, spinach and other dark leafy greens are full of vitamins A and C, as well as iron and calcium -- and oxalic acid. Too much of the naturally occurring chemical oxalic acid can cause burning of the throat, vomiting and diarrhea, difficulty breathing, convulsions, as well as coma and death. And if you live with gout or rheumatoid arthritis, expect that it can aggravate your symptoms.

Except for its fruit, all of which plant is toxic to people?

Except for its fruit, every single part of a tomato plant is toxic to humans. It's because the leaves and stems of the plant contain a compound called tomatine, which is an alkaloid that'll cause severe stomach distress as well as nerve damage.

Because it contains cyanide, never chew the pit of which fruit?

If you often suck or chew the pits when you're snacking on cherries, here's why you'll want to stop. With even the slightest injury to the pit, it produces prussic acid, which is cyanide. But don't freak out if you swallow a whole pit by accident -- if it's whole, it's much safer than if it's been crushed by your molars first.

Which type of nut contains as much as 9 mg of cyanide, per nut?

Sorry, although bitter almonds are some of the most flavorful almonds in the world and popular in many countries, they're packed full of the poison, cyanide. Before they can be eaten, they need to be processed for safety.

The high mercury levels in which type of fish make it a no-no for kids to eat?

Tuna is a source of healthy protein and it's high in omega 3 fatty acid. But you can't see that it also contains a toxic heavy metal that is known to cause neurological problems: mercury. Mercury most often accumulates in large predator fish, such as king mackerel, marlin, orange roughy, shark, swordfish, yellowfin tuna (also known as ahi), and bluefin tuna. And it's the mercury that tuna absorbs that's making this fish toxic to humans -- in fact, the danger is great enough that the FDA recommends children and pregnant women don't eat any tuna, at all.

Because it doesn't go through the pasteurization process, which food may contain a toxic compound called grayanotoxin?

Because it doesn't go through the pasteurization process, raw honey may contain a toxic compound called grayanotoxin. And grayanotoxins, which are found in the nectar of rhododendron plants, are known to cause mad honey poisoning, also known as "honey intoxication" or "rhododendrom poisoning." Generally, one tablespoon of "mad honey" is enough to cause dizziness, excessive sweating, weakness, as well as nausea and vomiting, lasting for at least 24 hours.

Which nut isn't sold raw because it contains a chemical also found in poison ivy?

The "raw" cashews you buy at the store aren't truly raw -- they've been steamed. Steaming removes a chemical called urushiol, which is a chemical also found in poison ivy -- and if it's not removed before you eat those cashews, you could have the symptoms of poison ivy although from a nut.

Which type of edible mushroom is often confused with the poisonous Jack O'Lantern mushroom?

Go to the store and come home with creminis, portobellos and button mushrooms. But go out foraging for mushrooms and you may find yourself running into look-a-likes. For instance, hunting for morels? Beware the toxic "false morel" mushrooms. And Chanterelle mushroom lovers should be aware that their favorite mushroom has a poisonous twin, called the Jack O'Lantern mushroom.

How can you neutralize the toxin in raw kidney beans?

Undercooked beans not only taste poorly, they may also contain a toxic compound called lectin (or phytohaemagglutinin). Kidney beans, for instance, are toxic raw, and become up to 5x more toxic heated to 175 degrees F -- just shy of boiling. It only takes three raw beans to cause symptoms such as nausea, vomiting and diarrhea. Boil them for a minimum of 10 minutes, though, and they're safe to eat. To avoid the problem altogether, choose canned beans.

Which fish contains potent neurotoxins yet is also a delicacy in Japanese cuisine?

Chefs will spend three years, sometimes more, training to prepare the blowfish, called fugu, which contains tetrodotoxin in its organs. It's typically eaten in winter, cooked in soup or raw as sashimi. If the chef gets it wrong, there is no antidote.

It's unsafe to eat raw lima beans because they contain what toxin?

Lovers -- and cookers -- of lima beans beware: Be sure to take a few safety steps when cooking limas. Raw lima beans, such as those that you buy dried, contain cyanide-generating enzymes that can only be rendered safe through cooking for at least 10 minutes.

Which starchy tuber, consumed mainly in Latin America, Africa, South Asia and the Caribbean, must be prepared properly to avoid cyanide poisoning?

Cassava, a starchy tuber also called yucca and tapioca, is one of the most consumed carbohydrates in the world, despite containing naturally occurring cyanogenic glycosides. To enjoy it safely, soon after it's harvested it must be dried, soaked, rinsed and properly cooked. Sweet cassava is 50 times less deadly than the bitter kind, but still has enough of the toxin to kill an adult cow.

Which berries should never be eaten when they're unripe or uncooked?

Even though they're commonly used in jams, jellies and wines, you need to be careful when consuming elderberries. The leaves and stems of the plant produce the poison cyanide (hydrocyanic acid), and when they're unripe or uncooked the berries contain a toxic alkaloid called sambucine. Not prepared properly, elderberries and elderberry products can cause nausea, vomiting, diarrhea and, in some cases, coma.

At 1,000 times more radioactive than many other foods, which is one of the most radioactive foods we eat?

Brazil nuts, which are technically seeds of the Brazil nut tree, are known for being rich in the nutrient selenium, and they look promising as a way to reduce total cholesterol. But because of the extensive root system of the tree, Brazil nuts contain natural amounts of radium, a radioactive element -- as much as 1,000 times more than bananas, potatoes, sunflower seeds and many other nuts.

Eggplant, also called aubergine, is part of the notoriously toxic nightshade family. Which of these statements is false?

Raw eggplants, themselves, aren't poisonous. But the plant they grow on, part of the nightshade family, contains an alkaloid called solanine -- and solanine, in large doses, can cause nausea, diarrhea, vomiting, stomach cramps, burning of the throat, cardiac dysrhythmia (an abnormal heart beat), nightmares, headache, dizziness, itching, eczema, thyroid problems, inflammation and pain in the joints.

Although they look like green tomatoes, which fruit grows inside a poisonous paper "lantern"?

They look like green tomatoes, but the tomatillo is actually related to the Cape gooseberry. There's some disagreement whether or not a tomatillo is toxic before its papery "lantern" peels off, or not -- regardless, before the lantern falls off the fruit is not yet mature, and still very sour. There is no debate, though, that every other part of the tomatillo plant, from that papery lantern to its stems and leaves, are poisonous. To safely eat them, you'll need to let the paper shell dry out, and the allow the tomatillos to yellow.

Which additive is used in the U.S. to make bread dough rise higher?

Because it can increase volume, potassium bromate is an additive often found as an in ingredient breads, rolls, and white "bromated" flour. But this oxidizing agent has been banned in every industrialized country except the United States and Japan. Potassium bromate is known to cause cancer in animals, and small amounts have been found to be problematic in humans -- it's linked to cancers, as well as kidney damage.

Which candy is 50 times sweeter than sugar, can turn your teeth black and possibly cause a heart attack?

Too much licorice is, it turns out, too much of a good thing. Licorice poisoning, called "glycyrrhizism" for the glycyrrhizic acid that gives licorice its flavor, can cause dangerously high blood pressure and dangerously low levels of potassium. How much black licorice is safe? Eating 2 ounces a day for 2 weeks is enough to cause a heart arrhythmia, or irregular heartbeat. Most of the candy we eat, though, is licorice-flavored -- it needs to be the real deal to pose a problem.

It's in a lot of the proteins we eat, but high amounts of what can cause hair loss and garlic breath?

Your body needs this essential trace mineral, but too much is potentially toxic. Selenium toxicity is caused by consuming too much selenium, but no one's sure how much is too much -- the RDA recommends a safe upper limit of 400 micrograms a day. Symptoms can include everything from hair loss and nail loss to diarrhea, fatigue, peripheral neuropathy, and skin lesions, as well "garlic breath" (without the garlic).

Which fruit has the most naturally occurring psoralens, compounds that can cause photosensitivity reactions?

Psoralens are naturally occurring substances that are part of a group known as furocoumarins. Citrus fruits are naturally packed with the compounds. But it's figs that are on the top of the list of foods containing psoralens, which, when consumed, put you at a higher risk for having photosensitivity reactions.

Which toxic substance is found in rice and rice-based products?

There are between 2.6 to 7.2 micrograms of arsenic in one serving of (inorganic) rice. It would take about 50 grams of arsenic to kill a 150-pound adult, and that's a lot of rice, but exposure to low doses over time are linked to bladder cancer and heart disease. Signs of arsenic poisoning include vomiting, abdominal pain and vertigo.

The chemical acrylamide is found in cigarette smoke, and also in which food?

Acrylamide is a chemical found in many starch-based foods, including bread and bakery products as well as potato products, that have been fried or baked to temperatures higher than 248 degrees F. Acrylamide is also found in coffee and in cocoa-based products. You can reduce your exposure to this carcinogen with small changes, such as skipping deep-fried foods and setting your toast to a lighter color.

Which licorice-flavored seed pod can be easily confused with its poisonous twin?

A good source of flavorful anethole, Chinese star anise is a commonly used ingredient in the U.S. and many other countries. But don't mistake it for Japanese star anise, which contains the neurotoxins anisatin and neoanisatin, as well as the neurotoxic sesquiterpene lactone veranisatins -- all highly poisonous to humans. Symptoms can range from vomiting and jitteriness to serious neurological effects, such as seizures.

Paralytic shellfish poisoning is a serious condition caused by eating shellfish that have been contaminated with what?

Paralytic shellfish poisoning is caused by eating shellfish -- clams, mussels, oysters, or scallops -- that have been contaminated with dinoflagellate algae, which produce toxins 1,000 times more potent than cyanide. Symptoms of PSP include drowsiness, tingling and numbness around the mouth as well as arms and legs, loss of motor control and incoherence. Dinoflagellate algae is also the reason for a red tide.

The roots and leaves have been used as herbal medicine for hundreds of years. But which plant is now banned in the U.S. for its toxicity?

Toxic pyrrolizidine alkaloids are produced by plants as a defense mechanism against insects, and comfrey contains enough to have been banned in the United States. Symptoms of toxicity include severe liver damage, which may begin as abdominal pain, nausea and vomiting, in addition to fatigue, loss of appetite and yellow skin or eyes. Although comfrey tea has long been used as a natural remedy, the World Health Organization reported finding instances of liver disease after ingesting 0.015 mg PAs/kg of body weight per day. The toxic range had been considered to be 0.1–10 mg/kg per day .

Which type of chili peppers contain the dangerous chemical capsaicin?

It's not the chili that's dangerous, it's the capsaicin. Extremely hot or fairly mild, every chili pepper you've eaten contains it -- it's also been used as the active ingredient in pepper spray, as well as in industrial paint stripper. Eat one hot one and you may feel sweaty and even a little queasy, but when you consume a lot of capsaicin, it causes gastrointestinal distress, as well as red, swollen skin. If too much is inhaled, it can cause the airways in your lungs to constrict, which could be fatal.

Which vegetable contains naturally occurring nitrates, believed to be harmful for human consumption?

In fact, the naturally occurring nitrates in celery can replace the synthesized form of sodium nitrite commonly used during the meat curing process. When the nitrates from the celery break down into nitrites, it adds the same cured flavor, the cured-pink color, and the same level of botulism protection. Other vegetables that naturally contain nitrates include beets, cabbage, carrots, lettuce and spinach, among others.

Opioid peptides are proteins can alter how we perceive pain and can affect our respiration. What food are they found in?

These foods contain proteins that, when broken down during digestion, produce opiate-like compounds that are able to act on your body's opioid receptors. And that can can alter how your body perceives pain, affect respiration, as well as impact your digestion and mood.

Known as the national fruit of Jamaica, a toxin in which fruit may cause "Jamaican vomiting sickness syndrome"?

It's the national fruit of Jamaica, and also eaten in other Caribbean nations, Central America and South America. But eating unripe (yellow, not red) ackee may cause "Jamaican vomiting sickness syndrome." It's the hypoglycin toxin in the unripe fruit that's to blame. Symptoms, including drowsiness, delerium, fever, loose bowels, repeated vomiting and thirst, begin within 6 to 48 hours, and may escalate to a dangerous drop in blood glucose levels, and problems with the muscular and nervous systems, leading to coma and death.

Which of these foods is considered "goitrogenic," meaning it enlarges your thyroid?

Raw foods that, when consumed, interfere with your thyroid's ability to use iodine -- which is needed for your cognitive function and correct hormone balance in your body -- are known as goitrogenic foods, and include broccoli, peanuts and strawberries, among many more. The lack of iodine resulting from, for instance, too much raw kale, can even affect your thyroid enough that a goiter forms.

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