Nightshade vegetables are notorious for causing autoimmune and digestive problems in a small part of the population. Many people who’ve eliminated them from their diet say they experience a remission of arthritis, a clearing of their skin, and sometimes even and improvement of digestive system problems like colitis, Crohn’s, and IBS.
After I adopted a raw food diet about 13 years ago as a means of beating the autoimmune disease colitis I was suffering from, it took me awhile to figure out why I sometimes still had problems with my digestive system and skin.
After a couple years I figured it out – the tomatoes I was eating multiple times a week and large quantities were the culprit.
Nightshade Vegetables: How Deadly Is A Wild Nightshade?
When I went to summer camp as a kid, my counselor warned us away from the red berries growing on several different plants and shrubs we passed on our hikes.
They were wild-growing members of the nightshade family, and just a handful could kill a child if they were eaten, he told us.
They contain alkaloids – chemical substances that work as pesticides to drive off or kill animals that want to eat them. Some also have glycoalkaloids, which are better known for poisoning people eating green, uncooked potatoes (potatoes are also a nightshade).
The fruit and leaves of wild nightshade plants still kill people in the modern era 12, and people have willingly eaten nightshades specifically to be poisoned and experience hallucinations for millentia; mandrake root is one example. The steroid alkaloids in these plants block certain nerve activity, which leads to muscle twitching, breathing changes, paralysis, and changes to human audio and visual perception.
What About Supermarket Nightshades?
Humans started domesticating nightshades thousands of years ago, and they weren’t stupid. They would have noticed if their newly-introduced foods were causing severe health problems. The domestication process involved breeding nightshade cultivars with ever lower amounts of alkaloids, and creating cultivars where the glycoalkaloid contents plummeted during ripening.
Today, billions of people eat nightshades daily with few apparent negative repercussions.
A minority of the population has nightshade allergies (different than an alkaloid sensitivity). A study of people consuming eggplant in India found that about 10 percent of participants reported itchy skin and/or mouths after consuming it. 5
Although multiple studies have looked for links between nightshades’ alkaloid content and and arthritis, so far there doesn’t appear to be a connection.
But there could there be another issue at play?
Lectins And Nightshades
The nightshade family has some of the highest concentrations of lectins among edible food.
As I’ve discussed before, lectins are a type of protein that can bind to cell membranes and trigger autoimmune conditions. They’re particularly known for causing serious issues in the intestines of those who are susceptible. I’ve discussed the science behind this this at length in this article and video.
Researchers have also documented effective methods of reducing the lectin content of certain lectin-rich foods, particularly legumes. I discussed that research in this video.
Since I’ve already noticed that nightshades cause me serious digestive problems (along with other lectin-rich foods), it raises the questions of if lectins are the element causing my issues. I’ve previously documented my attempts to reduce lectin content in beans, and noticed a reduction in symptoms. So will the same thing happen with nightshades? I decided to find out.
Nightshade Lectin Reduction
The available research on lectin reduction suggests a 24 hour soak in baking soda water and cooking in a pressure cooker brings about the biggest reductions in lectin content. This method worked well for my legume experiments.
You can’t really soak a tomato, through, so I just opted for cooking each food for a half hour in a pressure cooker with a quarter tablespoon of baking soda added in.
If I cook nightshades via boiling, I would get quick-disappearing skin rashes, acne, and serious digestive system problems. Nightshades usually leave me with diarrhea, bloating, and gas. If I rated their digestive disturbance ability on a 1-10 scale, with 10 being the worst, tomatoes, tamarillos, and tomatillos would be a 7-10 on the digestive system scale, while something like a potato or nightshade would be closer to a 3-7.
So how did the reduction method affect things?
The Tests & Results
For most of my previous experiments I tested a food at least a half dozen times, with breaks in between to allow my system to reset. With most of these nightshades, however, I could only bear to do the tests 2 times, except for potatoes and eggplants, which I tested six times, because they were somewhat less problematic.
A rating of 0 means it caused no problems. A rating of 10 means it was about as bad as it gets. A rating of 3-5 means that my rating were between 3 and 5 between various tests.
As you can see, the pressure cooking with baking soda brought about a significant reduction in symptoms, without completely eliminating them.
Tomatoes, tamarillos, peppers, and tomatillos were too problematic to be a realistic option, but I was surprised at how much better potatoes and eggplants were. I probably won’t be eating them, it was an interesting experiment. All these options are still significantly worse options than easy-digesting fruit, but not too shabby, all things considered.
If you’re looking to improve your digestive system, check out my book, The Raw Food Digestive Tune-Up.
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Wasserman RH. Active vitamin D-like substances in Solanum malacoxylon and other calcinotic plants. Nutrition Reviews 1975; 33:1-5 ↩
Davis GK. Effect of a nightshade (Solanum malacoxylon Send.) on calcium metabolism in livestock. In: Childers NF, Russo GM (eds.). The nightshades and health. New Jersey: Horticultural Publications, 1986; 144-157↩
Babu, B. N. Harish, P. A. Mahesh. Y. P. Venkatesh. A cross-sectional study on the prevalence of food allergy to eggplant (Solanum melongena L.) reveals female predominance. Clinical & Experimental Allergy 38(11):1795–1802, 2008. ↩