Nightshades Series 5 of 5: The Problem with Potatoes

Potatoes (Solanum tuberosum). They seem so harmless, right? Well, far from it! This article will be all about potatoes, mainly about their glycoalkaloids and the toxicity that has been demonstrated in human history, across multiple animal species and via multiple potential mechanisms. Sound familiar? Potatoes just may be the most dangerous food that westerners eat on a very regular basis. How is this so?

First of all, while not apparently related to glycoalkaloids, cooking potatoes results in high amounts of the carcinogenic compound acrylamide. In fact:

“According to FDA research, the top three foods with the highest mean acrylamide content were potato based. Products such as restaurant french-fries, oven-baked french-fries and potato chips could pose the highest risk to consumers.”

The whole list of the foods the FDA evaluated is here. As few folks are eating raw potato these days, the acrylamide issue (which is increased proportionally with higher cooking temperatures) is a pertinent one right off the bat. While this is not limited to potatoes
only, as the FDA list demonstrates, it is very significant with potatoes in particular.

Solanine is the major glycoalkaloid found in potatoes, along with alpha-chaconine. For a short and sweet synopsis of the glycoalkaloids in potatoes, see here. A very important fact is that “the clearance of glycoalkaloids usually takes more than 24 hours, which implicates that the toxicants may accumulate in case of daily consumption.” This fact alone puts a twist on acute (<24 hours duration) studies done on glycoalkaloid toxicity, as many people eat potatoes everyday, often multiple times a day when all potato-based food additives are accounted for.

Solanine is found in all edible members of the nightshade (Solanaceae) family—quick review includes tomatoes, potatoes, peppers, eggplant, paprika, Cape gooseberries, goji/wolf berries, and tobacco—and it is well researched and accepted that these glycoalkaloids are toxic to humans and animals in sufficient doses. Even the World Health Organization (WHO) has placed a “safe level limit” on the solanine content of potatoes at 20mg/100g fresh weight. Why did a limit on solanine content need to be created? Because of incidents like this:

“Seventy eight schoolboys became ill after eating potato at lunch on the second day of the autumn term. Seventeen of the
boys required admission to hospital. The gastrointestinal, circulatory, neurological and dermatological findings and the results of
laboratory investigations were in keeping with solanine poisoning.”

And this:

“Death has occurred in previous outbreaks, usually within 24 hours; but those cases were mainly in undernourished patients who may not have received adequate treatment... Possibly unrecognized mild solanine poisoning may be the cause of many mild episodes of “gastro-enteritis.”

Other references to this issue included Mass poisoning with solanine, Solanine poisoning, Potato poisoning, and A small outbreak of solanine poisoning. So, chalk up a Black Box history of potatoes/solanine poisoning people.

What conditions create a situation where glycoalkaloids reach toxic levels? They are phytoalexins (defensive antibiotic compounds) that increase in concentration in response to real or perceived threat situations to the plant. These threats include:

1. Potato blight—Caused by Phytophthora infestans, an oomycete (water mold) that attacks potatoes and other nightshades.
2. Light and heat—As potatoes are tubers (roots) grow underground in the cool darkness, exposure is perceived as a threat.
3. Mechanical damage.

Glycoalkaloid content also rapidly approaches toxic levels once the potatoes are greening or sprouting (chitting). It is estimated that 60-70% of the total glycoalkaloids present in most varieties of potato are contained within the peel (aka the “most nutritious part!”). I doubt I was the only college student who cut the sprouts off of potatoes and eaten them just to save some money! The big question then becomes, how well do you trust your grocer and their produce department to protect you?

What are the systemic effects of the glycoalkaloids, besides acute poisoning, you ask?

Solanine and alpha-chaconine from potatoes have both been shown to disrupt cell membrane function (1, 2, 3). The negative effects of this disruption may manifest in multiple areas of the body.

In the gastrointestinal tract:

1. Studies on intestinal cell lines (Caco-2) have shown effects upon gene expression and pathways related to cholesterol biosynthesis and growth signaling (1, 2).
2. Exacerbation of irritable bowel disease (IBD) in mice.
3. Necrosis of gastrointestinal tissue in Syrian hamsters (1, 2).
4. Inhibition of human pancreatic proteolytic enzyme activity.

The irritation of the gastrointestinal tract is particularly important in those who are gluten intolerant. In many gluten-free foods, potato starch is a common “replacement” flour—this alone could possibly thwart much of the improvement that one expects when they go gluten-free!

Hepatic (liver) effects:

1. Reduction of liver weight in mice—“The significantly lower liver weights of mice treated with alpha-chaconine and alpha-solanine and the significantly lower %LW/BW [liver weight/ body weight x 100, author] of mice treated with alpha-chaconine suggest that these effects may be due to hepatotoxicity.”
2. Liver gene mutations in pregnant mice.
3. Inhibition of normal human liver cells in vitro.
4. Destruction of normal human liver cells in vitro.

Red blood cell effects:

1. Red blood cell disruption.
2. Hemolysis (1, 2).

The relationship of glycoalkaloid teratogenicity has been relatively well studied in animals, including:

1. Frog embryos in vitro (1, 2).
2. Chicken embryos.
3. Mice:
a. Low birth weight and fetal abortion.
b. Fetal abortion, neural tube defects, growth retardation.
4. Toxicity in pregnant rats.
5. Birth defects in hamsters (1, 2, 3, 4, 5, 6)
6. In vitro inhibition of pre-implantation bovine (cow) embryo development.

As far as I can find, there are no direct studies on the relationship of potato or glycoalkaloid consumption and teratogenicity in humans. I wouldn’t let my wife in that study! After looking at the data in animals, who would let a pregnant woman potentially do that to herself and her unborn child?

Important question—If potatoes were not already in the food supply and were introduced today, would you let them in based on those animal studies? I hope not! There have been enough reviews on the relationship of potato blight to human birth defects, particularly in Ireland during times of potato blight to give one serious pause in regards to consistent consumption of the glycoalkaloids in potatoes (1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14). It is quite amazing to me how much unnecessary fear is drilled into pregnant women over medicinal herbs of all sorts, many based solely on conjecture, while no precautionary advice is being directed toward potato (and other nightshade) consumption!

Being that I started this whole series of articles on the connection between nightshades and arthritis, I’ll bring it back around to that point with potatoes as well as I can. The potato glycoalkaloids (remember, all nightshades share these compounds!) are potent acetylcholinesterase inhibitors. This has been shown in:

1. Insects.
2. Rabbits.
3. Horses.
4. And finally, humans (1, 2, 3, 4)

Could this be the main cause of their toxicity and ability to cause physical discomfort? Let’s investigate this further. What are some of the possible effects of acute (short-term) solanine poisoning?

Gastrointestinal disturbances, nausea, vomiting, diarrhea, abdominal pain, hypotension (low blood pressure), rapid breathing, delirium.

What are some of the effects of acetylcholinesterase inhibition?

Gastrointestinal upset, nausea, vomiting, diarrhea, abdominal pain, hypotension, bronchoconstriction, dizziness, fainting.

Do those sound close enough for you? One other notable action of acetylcholinesterase inhibitors on the neuromuscular junction is that they result in prolonged muscle contraction(s). I’m going to put out some conjecture that the typical “stiffness” found in all types of arthritis, especially osteoarthritis without inflammation, is simply prolonged muscle contraction(s)! Next, imagine what would happen in terms of mechanical wear to any system of moving parts that has increased friction (due to chronically increased muscular tension across joints). Mechanical wear would increase, correct? One mechanism can then explain two issues that are commonly found in arthritis.

For those who plan on eating potatoes (and the other solanine- and chaconine-containing nightshades) anyway, and you’re wondering if there is anything you can do or take to reduce their impact on your system, here are your possibilities—probiotics (especially L. plantarum) and folic acid. A naturopathic physician colleague of mine who practices Applied Kinesiology told me that whenever he found nightshade sensitivity in a patient he noticed that it was always accompanied by a vitamin B-6 deficiency.

On the vitamin note, folic acid is crucial in preventing neural tube defects before and during pregnancy. These malformations include spina bifida (open spine), meningomyeloceles, myeloceles, anencephaly (open skull), encephalocele (gap in the skull) and other anomalies. It also appears to be potentially protective against embryo damage from alpha-chaconine. So, a combination of a folic acid deficiency and a high intake of nightshade foods would spell real trouble for a developing fetus! If you missed the part regarding the documented history of potatoes and birth defects above, make sure to read that part again.

In conclusion, potatoes are just not worth the potential risk(s). If you are going to eat them:

1. Avoid eating the potato peel.
2. Do not eat greened, black, damaged, or sprouting potatoes.
3. If you have any doubt about the length of time (longer is worse) or temperature (warmer is worse) that the potatoes have been stored under, even if not green or sprouting, it is prudent to avoid eating them.
4. The more bitter the potato, the higher the glycoalkaloid content.
5. Pregnant women would do well to avoid all nightshades, potatoes in particular.
6. Realize that combinations of nightshades in dishes will increase the solanine content additively. Eggplant parmigiana with a side of gnocchi would be a bad idea.

Try switching to sweet potatoes (which unfortunately still carry an acrylamide risk likely higher than regular potatoes). Also try your old potato recipes with parsnips, as anything that can be done with a potato can and has already been done with a parsnip! Replacing mashed potatoes with steamed & mashed cauliflower equals no toxic glycoalkaloids, less carbs, and more nutrients!

All that and I never even went into the glycemic index and carbohydrate content issue...