Nightshades and inflammation, gut health and autoimmune disease

To eat or not to eat. When it comes to nightshades many people avoid them for one reason or another, and far more people enjoy them in their diet on a regular basis. With many people finding they can contribute to arthritis, inflammation, irritable bowel syndrome (IBS), inflammatory bowel disease (IBD) and other autoimmune disease symptoms. 

But what is it about nightshades that could be contributing to these various symptoms for people and what evidence is out there to help explain the relationship between nightshades and their influence on health? 

What are nightshades? 

Nightshades are a group of plants belonging to the Solanaceae family, there are many plants in this family, but common nightshade foods include potato (excluding sweet potato), tomato, eggplant, chili peppers, capsicum (bell pepper), goji berries and paprika. 

These foods contain many nutrients, vitamins, minerals, and beneficial plant compounds like antioxidants and polyphenols. They also contain other compounds including alkaloids and glycoalkaloids which have been shown to have potential toxicity and negative effects to human health. 

Today, I'm just going to be talking about glycoalkaloids, present in the highest quantities in potato, tomato and eggplant. We’ll save other alkaloids, more relevant when talking about chili and capsicum, for another day. 

What are glycoalkaloids?  

Glycoalkaloids help to protect nightshade plants from pests and disease. Research has shown both positive and potentially harmful effects of glycoalkaloids on health. The most common glycoalkaloids that also seem to have the most research available include α-chaconine and α-solanine in potatoes, α-tomatine in tomatoes, and α-solamargine and α-solasonine in eggplant.   

When consumed in high enough quantities these glycoalkaloids have the potential to cause negative effects in humans. Symptoms can include gut discomfort, nausea, vomiting, diarrhea, drowsiness, skin sensitivity, and in extreme cases, coma or death. 

Ever hear of green potatoes being poisonous?  

That’s because glycoalkaloids are produced in higher quantities because of the potato being exposed to sunlight. The glycoalkaloids in potatoes can also be higher with immaturity, aging, damage, storage at low temperatures, and frying. The risk of high glycoalkaloid content in potatoes causing issues to people consuming them has required regulations to be put in place with commercially grown potatoes. Only species that produce glycoalkaloids below a specific amount are allowed to be grown and sold for human consumption. 

Because the glycoalkaloids in potatoes are in their highest concentration in the skin, peeling helps to reduce the content significantly as well as boiling but for the average person, unless they’re eating huge quantities of potato daily, this shouldn’t be of much concern.  

Green tomatoes have been shown to have the highest content of α-tomatine, as they ripen, this gradually decreases with α-tomatine converting to tomatidine, the aglycone of α-tomatine/non-sugar portion of the glycoalkaloid molecule, which had been shown to be less toxic. 

In contrast, the glycoalkaloids present in eggplants have been shown to increase as they ripen. 

While some people can have allergies to different nightshade foods, the risk of actual dangerous toxicity is generally low, with regulations in place for potatoes and the highest quantity of glycoalkaloid content in nightshade foods generally present in parts of the plants we don’t eat like the leaves and stems. 

How nightshades could affect Gut health and Autoimmune disease 

For some people who eat nightshades, they can find they have digestive issues, joint pain, increased inflammation or flares in autoimmune symptoms. A theory of why this may occur is due to alkaloid/glycoalkaloid sensitivity.  

For some people, various alkaloids including glycoalkaloids may cause sensitivity because of the potential to disrupt the integrity of cells in the gut lining of sensitive people. There is research (in mice) that has shown glycoalkaloids can interact with cell membranes and cause damage, leading to a potential increase of intestinal permeability (leaky gut), immune response, and inflammation, which could contribute to gut and autoimmune symptoms. 

In these mouse studies a relatively high quantity of glycoalkaloids were used, in one study this was the equivalent of a plate of fried potato skins each day for 20 days, which is likely an unrealistic quantity for most people compared to average daily consumption. Lower intake of glycoalkaloids is likely to have lower effects, although for particularly sensitive people there’s potential even small amounts could contribute to symptoms and inflammation. * 

The most significant effects were shown on mice that were genetically predisposed to IBD, with mice not predisposed needing a significantly higher consumption before any negative effects occur. This may mean that people already predisposed to IBD or autoimmune disease, or people with gut issues, could be more likely to have nightshade consumption impact gut or autoimmune symptoms. *  

*In an ideal world, I wouldn’t be pulling evidence from mouse or animal studies as this doesn’t show human effects specifically. There is limited evidence available surrounding the effect of nightshades on gut health and autoimmune disease in humans, so I am using these examples to highlight possible mechanisms within the human body. Ultimately more research needs to be done in this area to fully understand this relationship in humans. 

Nightshades: Good or Bad? 

This is not a simple question to answer. Ultimately it depends on each individual and how nightshades may or may not influence any symptoms you may be experiencing. 

Nightshade foods have many beneficial components, vitamins, minerals, fibre, and phytonutrients like antioxidants and polyphenols, that can have positive effects on our health, with research showing anti-inflammatory and anti-cancer effects among other benefits, in various nightshades.  

For most people it is likely that nightshades are beneficial to include in a nutrient dense well-balanced diet with the many benefits from the nutrients and beneficial compounds they contain likely to outweigh any negative effects. 

Should you avoid nightshades? 

Ultimately more research needs to be done in humans to fully understand the biological mechanisms for why some people find they can’t consume some or all nightshade foods without causing symptoms. Much of the current research is in mice that really breaks down the potential mechanism, with very limited information in humans around nightshade consumption beyond effects of nightshade toxicity with very large amounts consumed. 

Nevertheless, ultimately if you feel that nightshades may be a trigger for symptoms, whether gut, inflammation or autoimmune disease related, it could be worth eliminating nightshades for a period, then trialing one at a time through reintroductions to see if any symptoms occur.  

If nightshades don’t cause any symptoms for you there is likely no need to be concerned about having them in your diet as they are a good source of many beneficial compounds and nutrients likely to benefit health more than any negative effects that may occur. 

Final thoughts 

If you think you might have some food sensitivities, have autoimmune disease or gut health issues, it could be worth removing nightshade foods for a while to see if things improve, with other foods having the potential to contribute to symptoms as well. When any food elimination is done, it is important to be mindful to still meet essential nutrient intake and that it is only done for a short period of time to assess any sensitivities and changes in symptoms.  

To be effective, this needs to be done strategically so you know exactly what you have changed while tracking symptoms to really assess any changes over time or with reintroduction’s. Because of this, it is best to talk with a nutritionist or someone who specialized in this area before making significant dietary changes. 

If there is no difference in symptoms, it is likely that you tolerate nightshades fine and they are not causing significant negative effects. Nightshade foods are a good source of beneficial nutrients, they taste great, and are good to include in a well-balanced diet for most people.  

As much as dealing with chronic illness, autoimmune disease and gut health challenges can mean that at times we have quite a restricted diet, the goal is to include as much diversity of nutrient dense foods, be able to enjoy the foods we eat, and allow ourselves to have the “sometimes” foods as well if we are able to tolerate them. 

If you're feeling stuck trying to figure out your autoimmune or gut health symptoms and want some guidance, book your Free 15-minute Wellness Investigation with me. We'll talk through what’s going on, look at how we can start getting to the root of your symptoms, and create a plan that helps you feel like yourself again. 

References 

Glycoalkaloids: Structure, Properties, and Interactions with Model Membrane Systems. https://doi.org/10.3390/pr7080513 

Naturally occurring food toxins. DOI: 10.3390/toxins2092289 

Naturally occurring glycoalkaloids in potatoes aggravate intestinal inflammation in two mouse models of inflammatory bowel disease. DOI: 10.1007/s10620-010-1158-9 

Nightshade Vegetables: A Dietary Trigger for Worsening Inflammatory Bowel Disease and Irritable Bowel Syndrome? DOI: 10.1007/s10620-023-07955-9 

Potato Glycoalkaloids Adversely Affect Intestinal Permeability and Aggravate Inflammatory Bowel Disease. DOI: 10.1097/00054725-200209000-00005 

Structural Impact of Steroidal Glycoalkaloids: Barrier Integrity, Permeability, Metabolism, and Uptake in Intestinal Cells. https://doi.org/10.1002/mnfr.202300639

Glycoalkaloids of Plants in the Family Solanaceae (Nightshade) as Potential Drugs. https://link.springer.com/article/10.1007/s11094-022-02731-x