Are potatoes deadly poisonous?!

Potatoes already have a well-deserved reputation as a fattening food but, are they also toxic?

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It is no surprise the fact that potatoes are associated with overeating, diabetes, obesity and heart disease1 given their high glycemic load. This means that they spike your blood sugar and insulin to rapidly plunge it down, making you feel hungry just after eating. What is not so well-known is that their glycoalkaloid content can be extremely harmful and acutely toxic to humans.

Glyco... what??

Glycoalkaloids are a natural-occurring pesticide that some plants produce in order to protect themselves when attacked by fungi, viruses, bacteria or insects. There are several types but the main ones found in potatoes are a-solanine and a-chaconine. There are two mechanisms by which they impair your health:

Firstly, they disrupt your epithelial barrier as they breach your cells by attaching to their cholesterol membranes. This could be detrimental to your mucosal immune system and your intestine, worsening or/and leading to conditions such as inflammatory bowel disease (IBD).^2,3

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Secondly, they are neurotoxins that hinder your body's capacity to regulate acetylcholine. This is a crucial neurotransmitter that sends nerve impulses from motor neurons to skeletal muscles activating muscle action. Glycoalkaloids stop the enzyme cholinesterase from breaking down acetylcholine, leading to an accumulation of the neurotransmitter and an overstimulation of the cells. As a result, you get a plethora of unpleasant symptoms which include⁴:

• Convulsions
• Delirium
• Diarrhoea
• Dilated pupils
• Fever
• Hallucinations
• Headache
• Loss of sensation
• Hypothermia
• Paralysis
• Shock
• Slow pulse
• Slowed breathing
• Abdominal pain
• Vision changes
• Vomiting
• Nausea
• Fatigue
• Death

Not only are glycoalkaloids responsible for acute toxicities but they can also accumulate in body tissues, especially in the liver, kidneys, heart, lungs, and brain.

In spite of the detrimental effects this chemical has, the oral toxicity is relatively low because of their poor absorption. Provided you have a healthy gastrointestinal tract, the solanine will be eliminated through the urine and faeces within 12 hours while your gut microbiome detoxifies your system by converting the toxin into solanidine, a less harmful compound⁶.

Food safety

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Human studies have shown that even 1mg of glycoalkaloid per kg of body weight can be noxious whereas 3 mg/kg might be deadly. The safety limit for glycoalkaloid content is about 20 mg per 100 g (<0.25Ib.) of potato. The peel (3 to >100mg/100g) contains 3 to 10 times more glycoalkaloids than the flesh (0.10 to 4.50 mg/100g).  Therefore, if you are going to consume potatoes you can dramatically reduce the toxic content just by peeling it. Avoid by all means eating the sprouts, any green area or unripe potatoes as they contain hazardously high amounts of the toxin.

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Storage conditions, namely light and heat, influence solanine concentrations. Try to keep them in a dark and cool place as light increases the synthesis of solanine by 20% , while temperature can do the same (at 24°C/75°F the rate of formation is 2 times greater than at 7°C/45°F).⁵

Unfortunately, the toxic content is not significantly lowered by any means of cooking. In fact, studies have shown that frying concentrates glycoalkaloids.³

Other related foods⁷

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Potatoes are part of the Nightshade (Solanaceae) Family which were not considered fit for human consumption before the 1800's given the toxicity of some varieties like the atropa belladonna (deadly nightshade). Other members of this family include tomatoes and eggplant.

Are they also poisonous? Not really or, at least, not as much:

Tomato glycoalkaloid levels drop drastically when ripen going from around 50 mg/100g in green tomatoes to about 0.5mg/100g in red tomatoes, making potatoes 20 times more toxic. There has not been conducted any human study, but the median lethal dose in rodents is 500mg per kg of body weight.

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Eggplants are considerably safer than potatoes as their solanine content goes from 1 to 2mg/100g. As with the tomatoes, I do not know about any human study but, in rodents, the median lethal dose is 1.75 mg per kg of body weight.

Nightshade sensitivity is a whole other topic that I will address in a forthcoming post.

References and recommended readings

1. "The Problem with Potatoes." The Nutrition Source. Harvard T.H. Chan School of Public Health, 24 Jan. 2014. Web.

2. Iablokov V, Sydora BC, Foshaug R, Meddings J, Driedger D, Churchill T, and Fedorak RN. "Naturally Occurring Glycoalkaloids in Potatoes Aggravate Intestinal Inflammation in Two Mouse Models of Inflammatory Bowel Disease." National Center for Biotechnology Information. U.S. National Library of Medicine, Nov. 2010. Web.

3. Patel B, Schutte R, Sporns P, Doyle J, Jewel L, and Fedorak RN. "Potato Glycoalkaloids Adversely Affect Intestinal Permeability and Aggravate Inflammatory Bowel Disease." National Center for Biotechnology Information. U.S. National Library of Medicine, Sept. 2002. Web.

4. "Potato Plant Poisoning - Green Tubers and Sprouts: MedlinePlus Medical Encyclopedia." Medline Plus. U.S. National Library of Medicine, 21 Oct. 2013. Web.

5. Cantwell, Marita. "A Review of Important Facts about Potato Glycoalkaloids." Agriculture and Natural Resources. University of California, Aug. 1996. Web.

6. Montario, Andrew. "Potato Glycoalkaloid Toxicity: Solanine." Safe Spectrum Lighting. Cornell University. Web.

7. Ede, Georgia. "How Deadly Are Nightshades?" Diagnosis: Diet. 6 Jan. 2013. Web.