Ask The Trainer #50 – Nightshades

Ask The Trainer #50 - Nightshades


Hi Chad:

There is so much conflicting nutrition and supplement information out there, it’s hard to know who and what to believe. My question is about nightshades (tomatoes, white potatoes, eggplant, etc.). I just read an article written by a naturopath, that claims nightshades should be avoided because they cause calcification in the body (joints and possibly in the cardiovascular system as well), leading to arthritic pain and inflammation. I eat a lot of tomatoes and white potatoes so I am concerned about this issue. What is your opinion?

Nicole Kent


Hi, Nicole. You said it! There is indeed an overwhelming amount of conflicting information regarding various types of foods, supplements, etc. These conflicting views undoubtedly make it extremely difficult to know what information you should trust and which you should disregard.

You can select virtually ANY type of food on the planet and, regardless of how healthy the reputation of that food is, you will still be able to find information suggesting that particular food is damaging to your health in some way or another. Right?

In other words, if you were to avoid every type of food some so-called ‘expert’ claimed was harmful, you’d starve to death because you wouldn’t be able to eat any food at all! Obviously, we all require food and nutrients to sustain life. So, giving up food simply is not an option.

I believe the key is to do your homework on various foods, then weigh out the advantages and disadvantages of each type so you can make an informed decision as to what you should or shouldn’t eat.

What Are Nightshades?

Now let’s talk about nightshades. Potatoes, tomatoes, eggplant, Goji berries, and peppers all come from the Solanaceae family, commonly known as nightshades. So how did nightshades earn such a bad reputation? Because they contain chemical compounds known as glycoalkaloids.

These chemicals are also found in small quantities in other foods such as cherries, apples, and sugar beets which are not classified as nightshades. Glycoalkaloids are bitter compounds that act as a natural pesticide to protect the nightshade plants from bacteria, fungus, viruses, and insects.

Glycoalkaloids kill insects by binding to the cholesterol within their cell membranes, disrupting the structure of those cell membranes. This causes cells to leak, or burst open, resulting in cell death.

Glycoalkaloids present another danger. They have the ability to block an important enzyme known as cholinesterase, which is responsible for breaking down acetylcholine in the body. Acetylcholine is a vital neurotransmitter that transfers electrical signals between nerve cells and muscle cells.

Chad ShawWhen cholinesterase is blocked, acetylcholine can accumulate and electrically overstimulate the muscle cells of the pests, leading to paralysis, convulsions, and death. This is basically how nerve gas used in chemical warfare works.


Now based on what you know so far, glycoalkaloids might sound like they are the equivalent of King Cobra venom. Well…not exactly! There are other positive aspects of these compounds worth mentioning.

For instance, glycoalkaloids are structurally similar to glucocorticoids such as cortisol. Cortisol has many important functions in the body. One of those functions is the ability to reduce inflammation. Animal studies have actually shown glycoalkaloids do, in fact, possess many of the same anti-inflammatory properties as cortisol.

Moreover, laboratory studies have demonstrated glycoalkaloids also possess antibiotic and antiviral properties. This makes sense considering this is what nature intended these compounds for in the first place. Additionally, several other laboratory studies have shown glycoalkaloids can trigger a process known as “apoptosis”, which is when cancer cells self-destruct.

This may sound great, but unfortunately, glycoalkaloids can cause healthy cells to do exactly the same thing. Currently, there are no animal or human cancer studies. So, there is still a lot of research that needs to be done on this topic before anyone can actually say glycoalkaloids could be advantageous in treating cancer.


Among the nightshades we typically eat, potatoes are the only ones considered a vegetable. On the other hand, tomatoes, eggplant, Goji berries, and peppers all contain seeds. Therefore, they are fruits. The glycoalkaloids in fruits are significantly less toxic than the glycoalkaloids in potatoes.

Potato consumption generally is not associated with illness. Likely because the amount of glycoalkaloids most people ingest on a daily basis is simply not high enough to result in any noticeable side effects. There are numerous cases of livestock deaths from eating raw potatoes, potato berries, and potato leaves. Fortunately, people do not eat these things.

Side Effects

However, there have been documented reports of people falling victim to glycoalkaloid poisoning from potatoes that have been improperly stored, green, or sprouting. At low doses, humans may suffer from some gastrointestinal complications like vomiting or diarrhea. At very high doses more serious symptoms, such as fever, low blood pressure, confusion, and other neurological problems, may occur.

So how much risk are we actually taking by eating potatoes? The GI tract has a hard time absorbing glycoalkaloids. This is one of the reasons most people may not become ill from consuming potatoes. So, if your GI tract is healthy, most of the glycoalkaloids won’t make it into your bloodstream.

If you eat potatoes every single day, glycoalkaloid levels can build up and accumulate in the body’s tissues and organs. This happens because it can take days, or sometimes even weeks to clear glycoalkaloids from the body.

The good news is there are some measures you can take when preparing potatoes that will drastically reduce the level of glycoalkaloids you ingest. Most of the glycoalkaloid content is in the potato skin, so peeling your potatoes will remove virtually all of it.

Also, glycoalkaloid levels can be high in unripe and sprouting potatoes. Carve out any greenish colored parts or eyes of the potato to limit your exposure.

Glycoalkaloids can withstand most methods of cooking and processing. In fact, deep frying will actually increase glycoalkaloid levels. So, fried products like potato skins and french fries can contain relatively higher amounts.

It’s worth mentioning that oiling potatoes will reduce the glycoalkaloid content by a few percentages. Also, microwaving reduces glycoalkaloids by around 15%.

Even considering the existing evidence regarding glycoalkaloids in potatoes, I personally have no intention of giving them up. But, I’m careful about how I select and prepare them.


What about tomatoes? Do they pose the same threat as potatoes? Nope! Actually, the glycoalkaloids in tomatoes happen to be 20 times LESS toxic than those found in potatoes. Tomatine is the primary glycoalkaloid in tomatoes. There has yet to be any dosage-related studies conducted on humans. However, studies performed on mice suggest that 500 mg of tomatine per kg of body weight, or 227 mg per pound is the median lethal dose.

Now, this doesn’t explain how much tomatine it would take to kill a 150 lb person. However, if you were to consider the notion of a 150 lb mouse, it would take 34 grams of tomatine to be fatal. Considering a ripe tomato contains roughly 5 mg of tomatine, it would take around 15,000 pounds of tomatoes to take out ‘Mousezillla’. As a 180 man, I feel pretty safe including tomatoes in my diet several times per week. In my opinion tomatoes are a superfood where the good heavily outweighs any ‘bad’.

Glycoalkaloids are mainly found in the skin of a potato. However, in eggplants, they are mostly in the seeds and flesh of the fruit. Eggplants Glycoalkaloids are more toxic than those in tomatoes. But, they are relatively non-toxic compared to those found in potatoes.

In mice, a lethal dose of glycoalkaloids is roughly 1.75 mg per kg of body weight. In the example of the 150-pound monster mouse, it would take approximately 13 pounds of eggplants to bring this beastly rodent down. Even if the same rule applied to a 150-pound human, no is going to eat 13 pounds of eggplant at one sitting! I typically only eat eggplant every now and then, so I don’t consider them to be any danger to my health.

Peppers and Goji Berries

As for peppers and Goji berries, I just can’t seem to find any solid information regarding their glycoalkaloid content. However, I’m guessing they would be in line with rest of the nightshade fruits which are relatively nontoxic when consumed in “normal” amounts.

I eat peppers on a very regular basis, and I have no intention of excluding them from my diet. Once again, I feel the health-promoting compounds found in peppers and Goji berries heavily outweigh anything ‘dangerous’.

To conclude, I want to point out that an individual’s tolerance to particular chemicals and compounds can vary across a very wide spectrum, ranging from those who are extremely sensitive, to those who are not the least bit sensitive and can tolerate significant amounts.

So far, there is zero evidence that proves consuming nightshades will lead to joint pain or will exacerbate conditions like arthritis, fibromyalgia, autoimmune disease, cardiovascular disease, etc. Some individuals in documented studies swear nightshades increased the severity of the symptoms they were experiencing. But, once again, no concrete evidence has linked the two.

If you suspect you might be suffering ill effects due to consumption of nightshades, I’d recommend eliminating them from your diet for 2-3 weeks to see if your symptoms improve. If they do, chances are you might be someone who is more sensitive to these foods.

Prove ‘Em Wrong,
Chad Shaw

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