If vegetables had publicists (which for all I know about marketing, maybe they do), nightshades would need a very good one in my opinion.
On one hand, they give us tomato sauce, roasted potatoes, smoky paprika, and spicy salsa. On the other hand, they belong to a plant family that includes literal poison. Super delicious but also maybe toxic sounds like a pretty rough sell, but hey that’s showbiz baby. Welcome to the complicated world of nightshades.
What Are Nightshades?
Nightshades belong to the Solanaceae family — a group of plants that includes both common kitchen staples and some historically infamous toxic species.
The edible members most of us know and love include:
Tomatoes
Peppers (bell peppers, chili peppers, paprika, etc.)
White potatoes (not sweet potatoes — important distinction)
Eggplants
Goji berries
The less dinner-friendly relatives include:
Atropa belladonna (Deadly nightshade)
Datura stramonium (Jimsonweed)
Tobacco
Yes, your marinara sauce and a medieval poison share a family tree. Use this information as you will. Also, according to my attorney you should know that that was just a joke, not actual advice.
Why Do Nightshades Have a Controversial Reputation?
Nightshades contain natural chemical compounds called alkaloids. These compounds serve as a defense system for the plant. Since plants can’t run from predators, they deploy chemistry instead.
The primary alkaloids in edible nightshades include:
Solanine (found in potatoes, especially when green or sprouted)
Tomatine (in tomatoes)
Capsaicin (the compound that makes peppers spicy)
In large amounts, some alkaloids can be toxic to any human. In the amounts found in properly prepared foods, however, they are generally safe for most healthy individuals. But “generally safe” and “universally harmless” are not the same thing — especially when we’re talking about autoimmune disease.
Before we get to that, let’s give credit where it’s due.
The Benefits of Nightshades
For many people, nightshades are nutritional overachievers.
Tomatoes are rich in lycopene, a powerful antioxidant associated with heart health and reduced oxidative stress.
Peppers are loaded with vitamin C — often more than citrus fruits.
White potatoes provide potassium, vitamin B6, and fiber.
Eggplant contains nasunin, an antioxidant that supports cellular protection.
Capsaicin, the fiery compound in chili peppers, has been studied for:
Supporting circulation
Boosting metabolism
Providing topical pain relief
Potential cardiovascular benefits
For the average healthy person, nightshades are not inflammatory to the point of becoming a problem. So why do some people feel dramatically worse when they eat them?
Nightshades and Autoimmunity: Where Things Get Inflamed
Autoimmune disease changes the rules.
In autoimmune conditions, the immune system is dysregulated. Instead of distinguishing cleanly between “self” and “invader,” it mistakenly attacks the body’s own tissues. This means the immune system is already primed, reactive, and easily stimulated.
Now enter alkaloids.
1. Alkaloids and Intestinal Permeability
Alkaloids can affect the integrity of the gut lining in susceptible individuals. A growing body of research highlights concerns that certain compounds in nightshades - like alkaloids - may contribute to increased intestinal permeability (this is often referred to as “leaky gut”).
Why does this matter?
When the gut barrier becomes more permeable, partially digested proteins and other particles can pass into the bloodstream. In a person, especially a person with autoimmune disease, this can:
Trigger immune activation
Increase systemic inflammation
Exacerbate autoimmune flares
For a stable immune system, this may not be a major issue. But for someone with autoimmune dysregulation, it can be like tossing gasoline onto an already smoldering fire.
2. Immune System Stimulation
Alkaloids can be biologically active compounds. In some individuals, they can stimulate the immune system rather than calm it.
For people with conditions such as:
Rheumatoid arthritis
Lupus
Hashimoto’s thyroiditis
Psoriasis
Inflammatory bowel disease
…even mild immune stimulation can amplify joint pain, fatigue, skin flares, or digestive symptoms.
It’s not that nightshades “cause” autoimmunity. It’s that they can worsen symptoms in certain individuals who already have immune dysregulation.
3. Joint Pain and Inflammatory Symptoms
Anecdotally and clinically, many individuals with autoimmune arthritis report reduced joint pain when eliminating nightshades. The exact mechanism isn’t fully established and agreed upon, but theories include:
Increased inflammatory signaling
Heightened immune response
Sensitivity to specific alkaloids
Large-scale studies are limited, but elimination protocols — including the Paleo Autoimmune Protocol (AIP) diet — remove nightshades precisely because they are common symptom triggers.
Important Warning Signs
Many people are walking around with autoimmune issues that they aren’t even aware of. Similarly, some people can be sensitive to nightshades even without an official autoimmune diagnosis. For those who are sensitive, the reaction can be significant and can include:
Increased joint stiffness
Digestive distress
Skin inflammation
Brain fog
Fatigue
Disrupted sleep
And because nightshades are so common (tomatoes and peppers are in everything), repeated exposure can mean repeated immune activation.
This is why some people feel dramatically better when they remove them — and dramatically worse when they reintroduce them.
What About Potatoes?
It should be noted, sweet potatoes are not nightshades, and are typically well tolerated even in autoimmune diets. Even for those especially sensitive, removing the skin of the sweet potato can solve any potential flare-ups or issues.
Botany remains unbothered by our confusion. That’s also showbiz, baby.
So Should Everyone Avoid Nightshades?
No. Probably not. Probably not, no.
For the general population, nightshades are considered nutrient-dense, antioxidant-rich foods with clear health benefits. But if you feel like you’re looking to get to the bottom of some health issues - poor sleep, poor skin, joint pain, etc. - then it won’t hurt to remove them for the standard 30 days and see how you do without them, and how you do when you reintroduce them.
But for individuals with autoimmune conditions — particularly those experiencing persistent inflammation — nightshades act as symptom amplifiers. The difference lies in immune regulation, and they should be avoided if not completely eliminated.