Are potatoes really poisonous – or perhaps even deadly – as some sources are reporting? Can tomatoes kill you?

The connection that ketchup and fries have to cigarettes is not what you’re expecting.

It has nothing to do with the addictive nature of eating junk food, but rather compounds in specific plants which are being reported as unhealthy and toxic. Side effects of severe fatigue, chronic joint pain, rheumatoid arthritis, psoriasis, and leaky gut may just be the tip of the iceberg according to many.

If you’re a lady, lookout for inflammation downstairs. Vaginal itching is said to be an allergy symptom of nightshades.

ashtray with cigarette buttsNow here’s something you will never hear during an anti-smoking PSA or bolded on a billboard…

Smokers are about 50% less likely to get Parkinson’s disease than lifelong nonsmokers (1).

That means you are twice as likely to get Parkinson’s if you’re a non-smoker.

Does that mean cigarettes are healthy for you?

Definitely not. Only around 1% of the population will get Parkinson’s during their lifetime. You’re far more likely to get heart disease, lung cancer, and other terrible diseases from puffing away. If you’re a man who smokes, you’re 23 times more likely to get lung cancer. For women, 13 times (2). Even when those things aren’t immediately lethal, they will diminish your quality of life.

The takeaway is not to smoke. Rather, it’s that something appears to be beneficial in tobacco, at least in tiny quantities. Believe it or not, research suggests it may be the nicotine (3).

As recently covered in Scientific American, nicotine may be “as benign as caffeine” on a stand-alone basis (4).

Yes, it is addictive, but the health consequences of smoking appear to be linked to the tar and other numerous carcinogens in cigarettes. Not to mention, there are other addictive compounds in them, too (5).

If this neuroprotective benefit exists, how can you get the best of both worlds – tiny amounts of nicotine for the benefit, without ever smoking?

Nightshade plants may be the answer.

Tobacco is a nightshade, as are several common vegetables you eat. All contain natural nicotine.

However, the amount of nicotine in foods we eat is only a tiny fraction versus tobacco…

nicotine content in nightshade foods

Smoking just ONE cigarette contains over 400 times the nicotine that you get from your daily dietary intake, on average.

That may explain why cigs are so addictive, but your plate of veggies isn’t. At least not literally.

These foods are the reason why even you as a non-smoker will have nicotine that’s detectable in your fingernails, toenails, and hair (6).

Number of People Tested Average Nicotine Content of Toenail (ng g⁻¹)
Smokers 14 1971 ± 818
Non-smokers 10 132 ± 82

As to why the top number is not 400+ times higher than the bottom number, it may have to do with factors such as the rate of absorption from air vs. food and secondhand exposure.

But if this brain benefit exists, how much do you need?

Probably very little, as research has found the rate of Parkinson’s is also lower in non-smokers who are only exposed to tobacco smoke secondhand, through the the air in their home or workplace environment (7).

As to how much nicotine you are exposed to in the workplace (for relevant jobs, like at a restaurant or bar), the median estimate was 2.7 microg/day of nicotine.

The above cited study also reports there is only 2.25 microg/day of nicotine from dietary sources. That means you get almost the same amount from eating food as you would secondhand in a workplace where smoking takes place.

Since even secondhand job exposure correlates with lower rates of Parkinson’s, it would suggest that the minuscule amounts you get from diet might be all you need for boosting your brain.

The tiny quantities from vegetables also mean you are not consuming enough to experience addictive side effects. It’s the best of both worlds.

As reported in the official journal of the American Neurological Association (8):

PD [Parkinson’s disease] was inversely associated with consumption of all edible Solanaceae [nightshade vegetables] combined, but not consumption of all other vegetables combined.

Of course you never hear people report that. Instead, they call it nightshade poison, because these foods contain tiny amounts of nicotine and other alkaloids. Potent allergens they say. They claim eating these plants causes inflammation and a laundry list of diseases.

All those accusations are false.

Those are just some of the many myths and lies being perpetrated against nightshades, which are actually healthy for you. Not just for vitamins and mineral content, but perhaps even more exciting benefits.

What are nightshade vegetables?

All plants within the Solanaceae family are called nightshades. Many are flowers, vines, trees, and other foods humans do not typically eat. There are a number of plants within this family which produce edible fruits and vegetables. A list of the most common are:

  • White potatoes
  • Tomatoes
  • Sweet and bell peppers
  • Hot chili peppers (all varieties)
  • Eggplant
  • Tomatillo
  • Tamarillo

  • Okra
  • Pepino melons
  • Cape gooseberry/ground cherry
  • Jerusalem cherries
  • Pepino
  • Paprika (it’s made from pepper fruits)
  • Ashwagandha

fresh eggplant, red and bell peppers, hot peppers, white potatoes, russet potatoes

Are sweet potatoes a nightshade vegetables? No. Typical yams, as well as white and Japanese sweet potatoes, do not belong to the Solanaceae family of plants.

Black pepper is not a nightshade. Nor white pepper, green peppercorn, long pepper, Sichuan pepper (Chinese coriander), and Tasmannia. Despite their name, these spices come from the PiperaceaeRutaceae, and Winteraceae families, which are different than the Solanaceae family that bell and hot peppers belong to.

Olives are not nightshades, but some are stuffed with pimentos (peppers) which would qualify as such.

Blueberries and strawberries are not a nightshade fruit, despite what some report. In the American diet, goji are probably the only Solanaceae berry you’re likely to encounter on a regular basis.

Other nightshade foods

making tomato gratinProcessed foods you may not expect will make use of the aforementioned list of fruits and vegetables, even when they’re not listed in the ingredients.

  • Starch, including modified food starch – It is typically derived from either corn or potatoes.
  • Baking yeast, beer yeast – Not always, but many make use of potatoes.
  • Cheese – Even though this is an animal-derived food, many shredded and processed cheeses add potato starch to avoid clumping.
  • Retinyl palmitate (vitamin A palmitate) – This synthetic form of vitamin A is often used to fortify milk and other dairy products.
  • Shellac wax – Used for confectionery and baking purposes, this wax secreted by lac insects (most often the Kerria lacca species) who may feed off goji berries, if coming from China or east Asia.

Why are nightshades called nightshades?

potato flower blossum with bee

It’s high noon and this potato flower is in full bloom.

Many sources claim the reason is because their flowers bloom at night. That is not entirely correct.

The exact reason why they are called nightshades cannot be answered using historical records and texts. The most probable reasons include:

  • Deadly nightshade, the common name for Atropa belladonna, which truly is a poisonous plant in this family. It has a long history dating back to at least the ancient Romans and the days of Greek mythology (9).
  • Blooming at night, which some do but not all.
  • Growing in the shade, another characteristic which some of the plants have.
  • Some species had been used in witchcraft, which is naturally associated with the night and darkness.
  • Since some species are poisonous, the name nightshade may infer they are associated with darkness and death.

Why are they considered bad?

Great question. For starters, categorizing them all within the Solanaceae family was not even possible until microscopes and more modern science during the past couple centuries.

how much population decreased from Irish potato famineCertainly, many of these were not considered to be evil or a poison throughout history. Look at white potatoes, which had been a staple of the Irish diet – as well as much of Europe – for at least the past several hundred years.

In fact, it was the lack of potatoes due to disease which caused the Great Famine of Ireland in the 1800’s (10). White potatoes were arguably the most important food in their diet!

In the late 1700’s, for a time tomatoes were considered to be a “poison apple” but it turns out that was because the aristocrats were eating them off pewter plates tainted with lead (11). The acidity of the tomato ensured that higher amounts of heavy metals leached off of the pewter plate and hence, they really were poisoned!

The concept that this entire family of plants is poisonous and bad for you is a new phenomenon, only in recent history. It largely stems from misunderstandings and myths which had spread like wildfire in the 80’s and 90’s.

Thankfully, the invention of the internet has squashed many, but droves continue to believe.

Even today, many naturopathic doctors and others that the public looks up to tell people with arthritis and other conditions to avoid eating them. They’re still following the old wives’ tales.

Given the unusually large number of misunderstandings about nightshade plants, one can see why and how this could happen.

1. Allergies, debunked

woman with allergiesIn theory, you can be allergic to any food containing proteins and pollens, however bona fide allergies for nightshades are rare when compared to the 8 most common food allergens; milk, eggs, fish, crustacean shellfish, tree nuts, peanuts, wheat, soy (12) (13) (14) (15) (16).

For those that do have a real nightshade vegetable allergy, it will not automatically apply to the other vegetables in this family.

For example, if someone is really allergic to tomatoes, it doesn’t mean the side will necessarily happen with white potatoes.

While some may believe they have an allergy to this entire family of foods, evaluations of the body’s histamine response prove otherwise. During an allergy, your body produces excess histamine to get rid of the substance in question.

Of course, that’s not to say digestive symptoms or adverse side effects like heart burn aren’t common with some of these. However, those are anatomical and biological problems. If a histamine response isn’t involved, it should not be called an allergen.

Unfortunately, many people throw around the term quite loosely these days to describe anything and everything that doesn’t sit right in their stomach as being an “allergy.”

In short, the chances you are allergic to one are rare to begin with. The chance that a person is allergic to every Solanaceae species has not been recorded in medical literature to date. You would be the first of 7 billion.

2. The lectin lie

The word “macrobiotic” was first used in a 1796 text by Christophe Wilhelm Von Hufeland, a German scholar who is most known for the book Art of Prolonging Life.

The food menu people think of today as being macrobiotic – like brown rice and plain land and sea vegetables – was ushered in by lshizuka, a Japanese army doctor who used the diet to allegedly heal many of his patients.

It was popularized by George Ohsawa in the 1930’s and towards the turn of the century, by the late Michio Kushi. He founded the Kushi institute and authored The Cancer Prevention Diet in 1994, among many others books.

The Kushi Institute very much discourages nightshades, as their website infers the consumption is “related to loss of natural immunity” and cites a doctor who says “a primary cause of arthritis” is regular consumption of potatoes, tomatoes, and eggplant (17).

Whether or not Mr. Kushi ever had arthritis is unknown by us, but what is known is that he died from pancreatic cancer around three decades after he published a book on how to prevent the disease.

how lectins work

Source: Department of Chemistry, UC Berkeley (18)

We don’t mean to beat up on a dead guy though. Overall, the macrobiotic diet offers excellent advice, especially relating to low glycemic and less processed foods. His books are still worth reading.

However, there are few things in the beliefs of this movement which don’t always jive with science. Or at least, they need to be revised and updated in light of more recent findings.

One of those is lectins. Not all, but many macrobiotic dieters shun them.

Lectins are low level toxins which are designed to deter some parasites and predators, but not all. They can accomplish this by latching onto specific types of sugars after they’re ingested.

In short, these sugar-binding molecules are meant to ensure the survival of a given species by making it an unpalatable food for some other species, but not every species.

Call it selective poisoning.

Beginning in the 80’s and 90’s, and continuing until today, many in the macrobiotic seemed to ramp up their hate of nightshades. Why? Because potatoes and grains were found to have high amounts of them. Many people call them poisonous due to their lectin content.

Sounds logical, until you fast forward a couple of decades.

Scientists now realize all species – every type of plant and animal – which has ever been analyzed, has been found to contain lectins.

The problem? Many in the macrobiotic world are still stuck in the ’80’s and 90’s, believing that white, as well as purple and red potatoes, are bad for you because of their lectin content.

Lectins in food are often destroyed by heat and even for those which aren’t, most are not toxic to humans or animals. Rather, it appears these defense mechanisms are often directed towards microscopic parasites like mold and fungus (which have completely different cell structures than humans do).

For example, cooked tomatoes have practically none remaining.

It is true that the solanum tuberosum agglutinin (STA) lectin in potatoes is at a seemingly high concentration of 6.5% (19). But just like how a big warehouse full of fireworks is not more powerful than a small nuke, scientists have discovered that the potency of each type may be more important.

The lectins found in vertebrates (i.e. meat, dairy, and eggs) have even more diverse biological activity than those which come from any plant.

lectin familes

Credit: Division of Molecular Biosciences, Imperial College London (20)

If you want to go on a lectin-free diet, you would be limited to water and air since all foods contain lectins. Potatoes and other nightshades are unfairly demonized for having them, probably because they were among the first foods in which scientists discovered them.

It can be a complex topic to wrap your head around, so please read more about lectins.

3. Irrational fear of alkaloids

Nicotine is an alkaloid and yes, it would probably be bad for you to use it as a nootropic in high doses, even outside of cigarettes (i.e. Nicorette gum). If for no other reason, you never want to be hooked or dependent on something.

dried spice bottles at grocery storeHowever the nicotine in nightshades is a unique situation. You won’t find nicotine in other families of plants, but you will find other alkaloids and they’re quite prevalent in the plant kingdom. Even some animals have them, like bufotenin in the skin of toads. There are thousands which have been identified to date.

Caffeine is an alkaloid too, naturally present in coffee beans, tea leaves, and kola nuts.

Many alkaloids are indeed dangerous. Quite a few are poisonous to the central nervous system (CNS). Some even have psychotropic and hallucinogenic properties.

On the flip side, many of the health benefits coming from plants – especially herbs – are due to their alkaloids.

For plants which demonstrate antibacterial, antiviral, antimalarial, and anticancer activity in research, often times it’s because of a specific type of alkaloid. The soursop cancer research being done is a good example.

If you want to believe nightshades are bad for you because they contain alkaloids, then by following that same rule, you would be against the health benefits of many plants, including some of the most popular herbs and spices you eat everyday.

Are nightshades bad for you, too?

As with any food, they’re not always safe for you.

The solanine alkaloid in potatoes can most definitely cause food poisoning. If you eat green potatoes or those with sprouts growing from them, you will be consuming a large amount of solanine (21).

In that scenario, the side effects of the nightshade vegetable can include severe stomach pain, vomiting, diarrhea, fever, headache, and delirium.

That’s why it’s bad to eat potatoes which have been in storage too long, especially since the heat of cooking does not destroy solanine.

But think about it… eating a piece of chicken past its expiration date can carry the same consequences too, right?

Whether it’s potatoes, chicken, or another food, if you eat them under normal conditions you will be safe. To gang up on potatoes because they cause poisoning when they are past their prime is not fair, since most fresh foods fall into that category, too.

stressed woman at airportAre your recurring migraines a result of the ketchup you eat?

That’s what one popular blog dedicated to migraines wants you to believe. That they are a “major trigger” and you should be on a nightshade free diet.

So can they cause headaches?

Check the U.S. government’s PubMed data pool of 27,000,000 or so pieces of published medical information – everything from articles in peer-reviewed journals to published laboratory studies – and you will come across no evidence that the entire Solanaceae family causes migraines or headaches. Ditto for nightmares and anxiety, as some others allege.

Nor will you find it associated with skin conditions like acne, rashes, hives, and eczema.

These vegetables cause gas and bloating no more than other types. In fact, you will likely experience fewer farts with tomatoes and eggplants than you would with broccoli, cauliflower, and others which are cruciferous (Brassicaceae).

diagram of osteoarthritis in the kneeCertainly the stories of it being a joint pain trigger must be true. The alkaloids are causing inflammation!

Or so they say.

Arthritis is yet one more problem which these poor fruits and veggies get blamed for unfairly. With potato poisoning, at least the story is half-way true in limited circumstances. With arthritis, the story is never true.

Mark Erwin, an assistant professor of orthopedic surgery at the University of Toronto who actually specializes in arthritis told this to Reader’s Digest (22):

“I’m not aware of any studies in peer-reviewed journals that prove or disprove that they affect arthritis.”

And a dietitian from the Arthritis Society of Ontario also told Reader’s Digest there’s “no scientific reason to avoid nightshades even if you have arthritis.”

Another myth, busted.

Speaking of bone health, they also get blamed for osteoporosis. The claim is that they are high in oxalates, which prevent the absorption of calcium.

gourmet chocolates made with cashew, almond, and pumpkin seedsIf that’s the case, it’s time to stop eating spinach and cocoa. Those two foods, as well as many others, have substantially higher amounts of oxalates than any commonly eaten nightshade contains.

Fortunately, you don’t have to give up any of the above.

Only those prone to kidney stones should avoid oxalates. For everyone else, it would take very high amounts of oxalates and absurdly low levels of calcium for there to be an adverse effect on bone density.

Plus, the problem with the American diet tends to be too much calcium. That causes your kidneys to work harder (as the excess needs to be excreted in urine).

A large study of nearly 24,000 people also found a high correlation between too much calcium and heart attacks (23).

The health benefits of nightshades

Enough scaremongering already. They’re really not bad for you!

Like any food, if you feel your body doesn’t handle them as well for whatever reason, then avoidance is certainly worth a try.

However, the myths they’re poisonous or more allergic are deterring people from experiencing the health advantages they may offer.

Lycopene is a rare phytonutrient in the plant world

Research suggests lycopene might offer preventive benefits against prostate cancer, kidney cancer, and heart disease (24) (25) (26).

heirloom tomatoesThe highest sources from vegetables are nightshades; tomatoes have the most at 3,025 µg per 100g, while red peppers have 484 µg.

You can find it in a few fruits too; guava, watermelon, papaya, and red grapefruit. However they have lots of sugar and aside from the lycopene and vitamin C, they measure low for other types of antioxidants.

If you’re still worried about lectins, unlike potatoes, the type of lectin found in tomatoes (lycopersicon esculentum agglutinin) is quickly broken down and destroyed by the heat of cooking.

But that’s not the reason we recommend cooking them.

Most antioxidants are destroyed by cooking temperatures, by not lycopene. Its bioavailability in your body is actually increased from being cooked. (27).

What is bile acid-binding?

And why should you care about it? As stated in a USDA report (28):

“To lower the risk of diet and lifestyle-related premature degenerative diseases and to advance human nutrition research, relative bile acid-binding potential of foods and fractions need to be evaluated.”

These acids are created in the liver from cholesterol. They are re-absorbed back into the system and when that occurs, it is believed to increase cancer risk. It’s a big reason why high fat diets can be bad.

For example, deoxycholic is a bile acid and higher rates of it have been associated with tumors in the colon. It is believed to be “important in colon cancer etiology” (29).

Think the side effects are limited to your GI tract? Think again.

These bile acids have been found to “influence the growth and steroid receptor function of human breast cancer cells” (30). Other types of cancers have been called out in medical literature, too.

Cancer prevention aside, eating more bile acid-binding foods may lower cholesterol and help prevent atherosclerosis.

Known as bile acid sequestrants, some LDL cholesterol-lowering medications work using this mechanism; colesevelam (Welchol), colestipol (Colestid), and cholestyramine (Questran, Prevalite).

Some of those meds are also used as part of a type 2 diabetes treatment regimen.

What are the best bile acid-binding foods? Steamed okra and eggplant are among the highest.

The aforementioned USDA report ranks the nightshade plants okra and eggplant as #2 and #3, respectively. Only steamed beets were higher. Bell peppers appear to have moderate bile-acid binding potential, too.

Spicy food fans, rejoice

chili peppers in basketGiving up ketchup is easy. But saying no to sriracha and hot sauce would take the joy out of eating for many.

Now you have an excuse to eat even more hot and spicy foods.

As mentioned on the Parkinson’s Disease Foundation website, in response to a study about nicotine (31):

“People who consumed any of the vegetables in the Solanaceae family once per day had a 20 percent reduced risk of PD [Parkinson’s disease], compared with people who ate all other vegetables daily, such as lettuce, carrots and cucumbers.”

But which Solanaceae fruit or vegetable is best for the dietary intake of nicotine?

Peppers have the highest amount. Whether the color is red, green, or yellow, research suggests they might offer the most neuroprotective benefits within this plant family.

But wait, the news gets even better for hot sauce fanatics who use it daily.

For those who ate peppers daily, they had a 50% reduced risk of getting Parkinson’s. That’s the same rate of reduction as seen with cigarettes, but without the side effects of smoking.

Be careful though, as almost every hot sauce on the market is loaded with sodium. Most of the popular brands have up to 300 mg per serving!

Whether you shop at Kroger or Whole Foods, the lowest salt brand you will likely come across is surprisingly Tabasco.

One teaspoon of Tabasco has:

  • Over 50% less salt than Huy Fong hot chili sauce, the original sriracha brand with the rooster on the bottle.
  • Over 65% less than Tapatio and Arizona Food’s Organic Harvest habanero sauce.
  • Over 80% less than Louisiana and Frank’s Red Hot Original Cayenne.

Whether it’s a mainstream brand like those, or some regional craft brand, look at their nutrition facts and you may be surprised to see that almost all are sodium bombs.

Even the brands marketed as “healthy” and organic are often just as guilty.

Our favorite low sodium option is Dave’s Original Insanity if you really like heat (like most of us here). Unfortunately, you can’t kick it up a notch further to the Ultimate Insanity, because that flavor is loaded with sodium.

If you need something milder, you can buy Brother Bru Bru’s organic African chipotle on Amazon. The product’s label says hot, but it’s more comparable to ketchup by our standards.
These statements have not been evaluated by the Food and Drug Administration. This product is not intended to diagnose, treat, cure, or prevent any disease.