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.
7. Rhubarb leaves
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.
9. Wild mushrooms
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.