Nightshades: What Are They and Are They Bad For You?
Nightshades: What Are They and Are They Bad For You?
The surprising truth about nightshade vegetables and your gut health.
On paper, tomatoes, peppers, and eggplants are some of the best foods you could eat- high in fibre, loaded with antioxidants, and beloved staples of the healthiest eating style out there, the hallowed Mediterranean diet. But for a growing section of the population, these colourful plants are more of a nutritional landmine than a superfood. Some claim that nightshade family vegetables are wreaking havoc behind the scenes and warrant cautious consideration from anyone with inflammatory issues, from digestive distress to autoimmune flare-ups.
So, what’s really going on? Are nightshades getting an unfairly bad reputation from social media influencers creating a scandal for the clicks, or are these common veggies quietly sabotaging your gut health and making other symptoms worse, too?
What Are Nightshades?
Nightshades comprise a vast botanical group known as Solanaceae that includes around 2,500 species, most of which aren’t edible. This highly eclectic family includes everything from the humble tomato and the ‘king of Ayurvedic herbs,’ ashwagandha, to the more sinister belladonna, aka ‘deadly nightshade,’ and the hallucinogenic and poisonous datura, aka ‘hell’s bells.’ Another very popular nightshade, used by almost 2 billion people many times a day, is tobacco. And potatoes are still even more popular, still. So clearly, nightshades are a pretty ubiquitous part of human life.
Edible examples include:
- Tomatoes and Tomatillos
- Eggplant
- White Potatoes (but not sweet potatoes)
- Peppers (bell, jalapeño, cayenne, paprika, etc)
- Okra
- Goji Berries
- Gooseberries
- Ground Cherries
- Pepino Melon
What these unlikely relatives have in common is that each contains small amounts of natural defence chemicals called alkaloids that help the plant survive in the wild by deterring insects and herbivores. And it’s well known that those same protective compounds can be lethal to humans in large amounts. The hotly debated question is whether normal, food-based concentrations of nightshade alkaloids are anything to be concerned about. And that’s where opinions differ dramatically.
What’s In Them, and Why the Concern?
The most notable nightshade alkaloids are:
Solanine & Chaconine These are the glycoalkaloids most often implicated in nightshade horror stories. Found in eggplant, potatoes and tomato stems, they serve as naturally evolved pest repellents by binding to cholesterol in cell membranes and then punching holes in them. That’s certainly bad news for bugs, but the million-dollar question is how much it applies to humans. Nevertheless, it is by this exact mechanism that nightshades can theoretically irritate the cells lining your digestive tract.
Solanine levels are highest in green or sprouting potatoes- the kind you’re told to throw away. And for good reason: the infamous 1979 case of 78 schoolchildren being poisoned (and 17 hospitalized) by green potatoes is still considered a teachable moment in toxicology circles. The FDA describes glycoalkaloid content safety thresholds in potatoes for this reason, but improper storage or aging can cause levels to spike.
At high enough doses, these compounds are outright toxic. At lower levels but with consistent intake, it’s also plausible that they could accumulate over time. And unlike many other plant toxins, cooking doesn’t neutralize them. In fact, deep frying concentrates solanine levels.
Capsaicin This is the fiery little molecule that gives hot peppers their spicy kick. In small amounts, it’s anti-inflammatory and even analgesic - that’s why it’s common in arthritis pain-relief creams. But in larger quantities, capsaicin may also act as a gut irritant, especially for those with mast cell activation issues, IBS, or IBD. The capsaicin example highlights a universal nightshade truth: it won’t be an issue for everyone, but can absolutely be an issue for some.
Nicotine Yes, it’s true- nicotine is in food, too. While edible nightshade foods contain only trace amounts of this neurostimulant alkaloid compared to cigarettes, they present a quirky reminder of what the botanical family shares. Unlikely to be harmful or even noticeable in dietary doses, the nicotine in veggies still reveals that the vast diversity of seemingly unrelated nightshades (like eggplant and tobacco) have some consistently common chemistry, after all.
Tomatine Tomatoes have their very own glycoalkaloid: alpha-tomatine. Like solanine, it may damage cell membranes in the gut, albeit to a lesser degree. Levels are quite a bit higher in green tomatoes than in ripe red ones, dropping from 500 mg/kg to 5 mg/kg as the fruit matures. So, if you’re eating a lot of salsa verde or fried green tomatoes, you might be getting a bigger dose than you think.
To make matters even murkier, in vitro science has demonstrated potential benefits to tomatine as well, such as tumour inhibition and leukemia prevention. In fact, this is true of solanine as well. So what’s going on?
Is There Any Real Evidence They’re Harmful?
While anecdotes of happy nightshade avoiders abound (including those from high-profile figures like Tom Brady), actual clinical evidence is limited- and mostly done on mice. However, it’s pretty consistent and hard to dismiss.
One 2002 study showed that solanine and chaconine worsened gut inflammation and aggravated IBD symptoms. A 2010 follow-up study found that deep-frying potato skins dramatically increased glycoalkaloid content triggered intestinal damage and significantly worsened colitis-related inflammation. More recent research has confirmed similar findings, and this has all raised red flags - especially in autoimmune communities particularly attuned to issues affecting gut health.
That’s why the initial stages of the Autoimmune Protocol (AIP), designed by Dr. Sarah Ballantyne, eliminate nightshades completely. Ballantyne explains that the glycoalkaloids found in nightshades have a detergent-like structure; part fat-soluble, part water-soluble. That combo gives them the ability to bind tightly to cholesterol molecules embedded in cell membranes, especially those lining the intestine. Once attached, these compounds can disrupt membrane integrity, creating tiny perforations in the gut wall.
Increases in gut permeability can then allow unwanted particles to leak into the bloodstream. The presence of these intruders can then in turn cause an immune cascade that can spiral into systemic and sustained inflammation.
To put it simply, glycoalkaloids might not just irritate your gut but physically destabilize it, making it more likely that your immune system will end up fighting the food you just ate. But again, this is all largely theoretical, and the only real direct evidence it’s real comes from anecdotes, animal models, or in vitro cell studies. Having said that, elimination diets that cut out potential trigger foods, including nightshades, have shown benefit in small human trials.
The Real Answer Depends on You
Exaggeration isn’t helpful, and nightshades aren’t really toxic in the way that wellness influencers might claim. It’s been estimated that you’d have to eat in the neighbourhood of 20 pounds of potatoes in one sitting to hit dangerously toxic levels of solanine (which is another way of saying that it’s impossible). And clearly, most people digest nightshades with no issues - indeed, many thrive on them.
After all, foods like tomatoes and eggplants are known to be extremely powerful for fighting chronic illness, loaded, as they are, with complex antioxidants, phytonutrients, critical micronutrients, and prebiotic fibre. Indeed, there is even evidence that, far from causing inflammation, they can be powerfully anti-inflammatory. Humans have also eaten them, and eaten a lot of them, for a long, long time. And it’s not hard to see how discouraging people from eating vegetables when we’re already not getting enough could be counterproductive to promoting healthy dietary habits.
On the other hand, absence of evidence is not evidence of absence, and it’s certainly not beyond the realm of possibility to think that compelling human proof that nightshades can worsen gut symptoms might emerge in the coming years. If so, it would confirm the anecdotal reports that some people are better off without the Solanaceae family in their meal plan. It might also solve some unanswered questions, like why countries that eat the most fried potatoes have the highest rates of IBD.
If you do suffer from an autoimmune condition, IBS, or other unexplained gut symptoms, it’s not unreasonable to do your own controlled experiment to find out if any of this is relevant for you. While there’s no reliable lab test for nightshade sensitivity, and many standard food allergy panels won’t catch this kind of reaction, you still have options.
The best approach? A short-term elimination diet followed by careful reintroduction, ideally with guidance from a nutritionist or practitioner familiar with this territory. Starting a food journal, cutting out nightshades for 2–6 weeks, and then reintroducing them one at a time- watching for any flare-ups- might be profoundly illuminating. You may find, for example, that tomatoes are no problem, but potatoes are. Or vice versa. You won’t know until you test.
In the final analysis, the curious case of nightshade veggies is an excellent example that nutrition is not a one-size-fits-all proposition. It’s entirely possible that, by whatever mechanism, some generally healthy foods aren’t going to work for everyone. Honing in on what serves you and what doesn’t is the way to harmonize generally sound nutritional principles with your own unique constitution.
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