The potato (Solanum tuberosum) is a globally important food crop, yet it belongs to the nightshade family, which includes many toxic plants. The leaves of the potato plant are poisonous and should never be consumed. Toxicity extends beyond the foliage to various other parts of the plant, excluding the edible tuber when properly harvested and stored. This toxicity acts as a natural defense mechanism against pests and disease.
The Chemical Explanation for Toxicity
The poisonous nature of the potato plant stems from glycoalkaloids, primarily alpha-solanine and alpha-chaconine. These molecules are naturally synthesized by the plant as a defense against herbivores, insects, and fungal pathogens. These two main glycoalkaloids account for about 95% of the total toxic content.
Glycoalkaloids exert their toxic effect through a dual mechanism in the human body. They disrupt cell membranes, particularly those lining the gastrointestinal tract, leading to local irritation and cellular damage. These compounds also inhibit the enzyme acetylcholinesterase, which breaks down the neurotransmitter acetylcholine in the nervous system. This inhibition can disrupt nerve signaling, contributing to the systemic symptoms in severe poisoning cases.
Which Parts of the Potato Plant Pose a Risk
The highest concentrations of toxic glycoalkaloids are found in the non-edible parts, including the leaves, stems, flowers, and berries. Leaves naturally concentrate these defensive compounds. Concentrations in the leaves and stems can be up to 100 times higher than levels found in a healthy, edible potato tuber.
The tuber is generally safe when harvested properly, but its toxicity can increase due to environmental factors. Exposure to light causes the tuber to turn green, which indicates the formation of chlorophyll. While chlorophyll is harmless, its presence signals that the tuber has also begun to synthesize high levels of glycoalkaloids as a stress response.
The concentration of toxins is highest in the skin and just beneath it, especially in the “eyes” or sprouts. To minimize risk, any green parts, sprouts, or damaged sections should be cut away before cooking. Heavily greened or shriveled potatoes should be discarded entirely, as peeling may not remove all the toxin. Storing potatoes in a cool, dark, and dry place prevents the formation of these dangerous compounds.
Symptoms and Necessary Action Following Exposure
Symptoms of mild to moderate glycoalkaloid poisoning involve gastrointestinal distress, appearing 30 minutes to 12 hours after consumption. Initial signs include a burning sensation in the mouth, nausea, vomiting, abdominal pain, and diarrhea. These digestive symptoms are a result of the toxins irritating the lining of the stomach and intestines.
In rare instances of severe poisoning, neurological symptoms can occur. These may include headache, drowsiness, confusion, or restlessness. The toxic dose for humans is cited as 2 to 5 milligrams of total glycoalkaloids per kilogram of body weight.
If accidental consumption of potato leaves or other toxic parts occurs, seek professional medical advice. Contacting a poison control center or emergency services is advised, even if symptoms appear minor. Mild cases resolve within 24 hours, but medical guidance is necessary to monitor for any severe neurological effects.