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Many of us have been guilty of buying a huge bag of potatoes, using a few, and leaving the rest sitting in the bag for a month before we remember they're still there. Now the month-old potatoes are green and have little sprouts growing out of them. Why are they green? Are the sprouts poisonous? Can you still eat them?
Potatoes contain two kinds of glycoalkaloids, both natural toxins, called solanine and chaconine. Exposure to light greatly increases the formation of chlorophyll and glycoalkaloids. Chlorophyll is responsible for the green color of many plants and is not toxic. However, the green of chlorophyll is a marker that can indicate that there could be an excess of glycoalkaloids.
The entire potato plant contains glycoalkaloids, but the highest concentration is found in the leaves, flowers, "eyes," green skin, and sprouts. The lowest concentration is found in the white body of the potato. Toxicity is increased by physical injury to the plant, immaturity (green potato), low storage temperature, and storage in bright light. Cooking potatoes by baking, boiling, frying, and microwaving does not eliminate glycoalkaloids. However, removing the skin before cooking can reduce the glycoalkaloid content in a raw potato.
Both solanine and chaconine cause toxicity through cell disruption leading to gastrointestinal symptoms such as vomiting, abdominal pain, and diarrhea. Some people may also experience headache, flushing, confusion, and fever. There have been a few cases of death from eating toxic potatoes. The onset of symptoms is typically within a few hours but can be as delayed as long as a day.
The majority of patients with mild symptoms can remain at home. If symptoms are severe and persistent or if you are unable to hold down fluids, medical attention might be needed.
Glycoalkaloid toxicity from potatoes can be minimized by only buying potatoes as you need them, storing them in a cool and dry place, and peeling them before eating them. The advice for avoiding any type of foodborne illness applies to potatoes: when in doubt, throw them out.
If you suspect someone is having symptoms from eating a bad potato, check the webPOISONCONTROL® online tool for guidance or call Poison Control at 1-800-222-1222.
Diana M. Pei, PharmD
Certified Specialist in Poison Information
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