Health Tips - Nightshade Poisons
Some plants naturally produce toxins to defend themselves against insects, fungus, and animals. For example, many plants in the nightshade family contain naturally-occurring poisons called “glycoalkaloids”.
Some nightshades are poisonous enough that you wouldn’t think to eat them, such as deadly nightshade or belladonna, mandrake, petunias, and tobacco. Some nightshades, such as potatoes, eggplants, and tomatoes, have parts you shouldn’t eat.
One of the glycoalkaloids in the nightshade family is called solanine. Solanine can be found in many of the leaves, fruit, and tubers of these plants. A tuber is the thickened, rounded part of an underground stem of a plant, such as a potato.
Solanine can kill fungus and pests, and in large enough quantities, it can kill humans. It mainly affects the gut and nervous system. Symptoms can include nausea, diarrhea, vomiting, stomach cramps, heart rhythm problems, weakness, headache, and dizziness. In severe cases, hallucinations, loss of sensation, paralysis, fever, jaundice, dilated pupils, and an abnormally low body temperature have been reported. Symptoms can occur anywhere from 30 minutes to 12 hours after eating high-solanine foods.
Potato leaves, flowers, stems, and shoots are high in glycoalkaloids and should never be eaten. In potato tubers, most of the solanine develops in and close to the skin. When potato tubers are exposed to light, they turn green and increase glycoalkaloid production to prevent the uncovered tuber from being eaten. While commercial potatoes are screened to ensure low solanine levels, that level can change if the potatoes are exposed to light. So the green color, which is from harmless chlorophyll, tells of an increased glycoalkaloid level.
A bitter taste in a potato is also an indicator of glycoalkaloid. If potatoes cause a bitter taste or a burning sensation in the mouth, stop eating them. Never eat potatoes that show signs of greening, physical damage, rotting, or sprouting. Most cases of potato-solanine poisoning involved eating green potatoes or drinking potato-leaf tea.
A life-threatening dose for an average-weight adult is about 400 mg solanine. The U.S. National Toxicology Program says that the average American eats at most 12.5 mg per day of solanine from potatoes. In other countries the solanine level in potatoes can be much higher.
Eggplants contain very low levels of solanine. The younger fruit has the higher concentrations.
A 2008 study of 741 people in India found that nearly 10% reported some allergic symptoms after consuming eggplant. Inflammation and itchiness of the skin from contact with the eggplant leaf and flower have also been reported.
To reduce eggplant toxins only use very ripe eggplants, peel the skin, and soak for a couple of hours in very salty warm water, rinse and soak again.
It is possible that the fruit of the tomato plant does not contain any solanine at all. Green unripe fruit, tomato leaves, and stems, contain another mild glycoalkaloid that can be toxic if ingested. Ripe tomatoes do not contain these chemicals. Do not use tomato leaves, stems or green, unripe tomatoes!
Many people who have conditions involving swelling and pain, get relief by not eating certain nightshades at all. If you have any question about whether you should or should not eat potatoes, eggplants, and tomatoes, read the health tip Owner’s Manual to help you decide.
Only eat the right parts of plants in the nightshade family!