Vegetables That Should Only Be Eaten Cooked

Also known as manioc and yuca, this versatile tuber is a staple throughout much of its native South America and in parts of Africa and Asia and 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 remove 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 the 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 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 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 concentrations in raw kidney beans. Heating them insufficiently, as in malfunctioning slow cookers, can increase their toxicity — but thorough cooking renders them harmless.

Raw lima beans are like cassava in that they 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.)

When there are so many ways of eating cooked potatoes it is hard to see why anyone would want to eat them raw in the first place. You can roast, fry, boil, saute, or add them to casseroles. Eating them raw is a very bad idea as they contain high concentrations of solanine. If you ingest too much of this substance you can get nausea, diarrhea, arrhythmia, dizziness, hallucinations, paralysis, and hypothermia. You can spot potatoes that have an especially high concentration of solanine because they will be green. It is best to give these a miss even if you are cooking them.

Rhubarb stalks are delicious when eaten cooked but eating them raw is a very unpleasant experience. Do not confuse them with celery stalks which are a similar shape but an entirely different color and a totally different plant. You also should not eat the rhubarb leaves as they contain high concentrations of oxalic acid. This can make your throat burn and give you 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.