Never Eat These 9 Vegetables Raw

This versatile tuber, also known as manioc and yuca, is a staple throughout much of its native South America and in parts of Africa and Asia. (It is also the source of tapioca.) There are two main varieties, sweet and bitter, but both contain a cyanogenic glucoside called linamarin, which decomposes into poisonous hydrogen cyanide. In sweet cassava, the poison is concentrated near the surface and peeling and cooking removes all traces of it. It’s laced throughout bitter cassava, however, and that tuber must be grated, thoroughly washed, and pressed before cooking to remove it. Needless to say, neither kind can be eaten raw.

Eggplant is a member of the nightshade family (one of its relatives is so-called deadly nightshade, also known as belladonna), and like other family members contains solanine, a bitter-tasting steroidal compound. Too much solanine can cause nausea, dizziness, and other health problems, and extremely high doses can be fatal. Cooking eggplant lessens its solanine content, however, and anyway most authorities agree that you’d have to eat unreasonable amounts of the vegetable to experience ill effects. Nonetheless, some people are allergic to even small quantities of the compound, so it’s safer not to sample eggplant raw.

There are more than 130 varieties of green beans, and they are generally considered a very healthful vegetable, full of vitamins A, C, and K. Eating a few of them raw in a salad shouldn’t be a problem, but they’re mildly toxic unless cooked. They also contain lectins — so-called antinutrients that limit the body’s ability to absorb vitamins and minerals, and may cause digestive issues. Cooking reduces these to negligible amounts.

There’s actually an illness called red kidney bean poisoning, characterized by extreme nausea, diarrhea, and abdominal pain. This is caused by a toxin called phytohaemagglutinin, present in high concentration in raw kidney beans. Heating them insufficiently, as in malfunctioning slow cookers, can actually increase their toxicity — but thorough cooking renders them harmless.

Like cassava, raw lima beans contain linamarin, which decomposes into cyanide. Limas sold commercially in the United States are required by law to have lower levels of the compound than those grown elsewhere, though, and thorough cooking neutralizes the poison. (The beans should be cooked uncovered to allow the linamarin to escape as vapor.)

Like eggplant and other members of the nightshade family, potatoes contain solanine. Consuming too much of this compound can cause a variety of gastrointestinal and neurological problems, including nausea, diarrhea, arrhythmia, dizziness, hallucinations, paralysis, and hypothermia. Potatoes that are turning green have particularly high levels. Some methods of cooking — primarily deep-frying and boiling — noticeably lower solanine levels, and in any case it has been estimated than a 100-pound person would have to eat a pound of fully green potatoes to experience any ill effects. On the other hand, the high starch content of potatoes makes them hard to digest even when cooked — yet another reason to avoid them raw.

Rhubarb stalks, which look like overgrown red celery, make delicious pie (often combined with strawberries) and other desserts, but it’s very important to trim every bit of leaf from the stalks before you use them. (It’s a good idea to wash the stalks thoroughly, too.) While rhubarb itself is perfectly safe, and can even be used medicinally, its leaves have a high concentration of oxalic acid, which can cause a host of unpleasant symptoms, including burning throat, nausea, and diarrhea.

Many of us have eaten raw spinach salads with no ill effects. But spinach, like rhubarb leaves, contains oxalic acid, which limits calcium absorption and may facilitate the formation of kidney stones. Cooking the spinach and discarding the cooking water gets rid of most of the acid. Another issue with the raw leaves is that spinach is particularly susceptible to contamination with E. coli and other bacteria — again largely destroyed by cooking.

Cultivated mushrooms are fine to eat raw, and make good additions to salads. Restaurants, especially in Europe, sometimes serve certain varieties of wild mushrooms raw, as well, but in general the practice is unwise. They’re hard to digest, for one thing. Also, many varieties are mildly — or seriously — toxic when raw and become safe to eat only when cooked. Unless you’re an experienced mushroom hunter, it’s best to avoid them raw.