IIf you’ve ever gone down the rabbit hole of health and wellness trends online, you’ve probably come across the so-called shady side of nightshades: vegetables like tomatoes, potatoes, eggplant, and peppers. What has suddenly made them newsworthy is that they have been singled out by self-proclaimed wellness experts and celebrity dieters as the culprits behind a range of health problems, from arthritis to autoimmune disease flare-ups and indigestion.
Although there is little scientific evidence to support these claims, some people report feeling better after eliminating nightshades from their diet. So before you look at your salad, eggplant parmesan and baked potato, it’s worth taking a closer look.
Why have nightshades become so controversial (and where does that obscure name come from anyway)? Scientists, internal medicine physicians and registered dietitians are shedding light on these unfairly maligned vegetables.
What are nightshade vegetables?
Nightshade vegetables come from the Solanaceae family of flowering plants, which are nutritional powerhouses, packed with vitamins (like C and K), minerals (like potassium and magnesium) and fiber. Dietitians and doctors recommend them in abundance. In fact, they’re some of the key components of one of the world’s healthiest eating plans: the Mediterranean Diet.
Here lies the suspicion: These vegetables also contain alkaloids, which are natural chemicals produced by plants that are believed to deter predators. Alkaloids, such as solanine in potatoes and eggplant, tomatine in tomatoes or capsaicin in peppers, are consumed in very high concentrations and can cause symptoms such as vomiting, diarrhea and stomach pain.
This has led to discussions about its effects at each dose. Joe Schwarcz, director of McGill University’s Office for Science and Society and author of A grain of salt: the science and pseudoscience of what we eat, explains that although nightshades contain alkaloids, the amount they typically contain is of no importance. For example, although potatoes, which are eaten by a billion people worldwide, do contain solanine, the amounts are only found in trace amounts, he says. According to the University of Nebraska, an average amount of solanine in the skin of a potato means that a 200-pound person would have to eat 20 pounds of potatoes to experience toxic levels.
read more: Why Your Diet Needs More Fermented Pickles
However, there is a higher concentration of alkaloids in green, sprouted potatoes. Therefore, it is important to store them in a cool, dark place and discard the green and sprouted potatoes. During the Great Famine in Ireland in the 19th century, people ate a lot of potatoes that had been improperly stored for a long time, Schwarcz says. “But that doesn’t happen in North America. We don’t see potato poisoning, tomato poisoning or eggplant poisoning. We just don’t see it.”
These vegetables also contain lectins, Schwarcz notes, and while lectins can cause indigestion in some people, for the vast majority they are harmless.
The name “nightshade” comes in part from the infamous Belladonna plant, also known as the “deadly nightshade” because it contains a highly toxic alkaloid called atropine, which was historically used as both a poison and a medicine. This connection has given rise to myths about the toxicity of nightshade vegetables. “The fact that the tomato and the potato belong to the same botanical family as the Belladonna does not mean that they are equally poisonous,” says Schwarcz.
The Tik-Tok Effect: Claims vs. Science
On social media, you’ll find no shortage of videos and blogs vilifying nightshade vegetables, with titles ranging from “Foods to Avoid If Your Pup Suffers from Arthritis” to “These Vegetables Could Make Your Eczema Worse!” Most are the work of influencers and “self-proclaimed nutrition gurus,” Schwarcz notes. According to him, these makers range from ‘total incompetence… to doctors who have gone astray’. There are also many testimonials from people with autoimmune diseases like lupus, psoriasis, and inflammatory bowel disease (IBD) who swear they feel better when they avoid nightshades. Although medical and nutrition experts suggest that some people would likely benefit from an elimination diet, blanket warnings against nightshades are not warranted.
Dr. Rebecca Kuang, an internist at the University of Pittsburgh Medical Center, has studied the link between nightshades and gastrointestinal diseases. A literature review she co-authored last year found that the natural chemicals in these vegetables could disrupt the intestinal barrier and potentially worsen symptoms in people with certain intestinal diseases such as IBD. Many of the studies in the review took place in mice, but if the findings apply to humans, eating too many of these vegetables could worsen symptoms in people with certain intestinal diseases such as IBD.
read more: Why you suddenly have allergies
Nightshades also contain potential allergens that can cause reactions similar to other food allergies, with cross-reactivity between foods in the nightshade family and others. Kuang’s research shows that nightshades can cause the activation of mast cells, which can lead to inflammation and discomfort in the gastrointestinal tract, similar to an allergic reaction.
However, research in this area is still new, with many studies relying on animals or involving variables that could influence results. For example, Kuang is interested in how the preparation of a nightshade vegetable, such as high-fat baked potatoes, may affect some of the alkaloid levels. More basic scientific and human studies are needed, she says, to fully understand how nightshade foods can irritate the gastrointestinal tract.
“I wouldn’t want everyone to have to avoid these foods,” she says, “but certain people may be sensitive to them.”
What should you do if you suspect you have an intolerance or allergy to nightshade vegetables?
Navigating the complicated issues of food sensitivities, allergies and intolerances can be tricky, especially when it comes to nightshades. Diet and nutrition experts emphasize the importance of a personalized approach rather than broad exclusions. Lona Sandon, associate professor in the department of clinical nutrition at The University of Texas Southwestern Medical Center, brings a personal perspective to her professional insights, having lived with rheumatoid arthritis, an autoimmune disease, for 30 years. “It’s been folklore for a long time,” she says, adding that she has tried eliminating nightshades herself, along with many other foods, but to no avail. “There wasn’t enough fish oil in the world, not enough fruits and vegetables in the world, that would solve the problem with my immune system,” she says. Despite decades of debate, evidence about the nutritional impact of nightshades has not increased much. “In fact,” says Sandon, “there is more research supporting that people should include these foods in their diet if they have inflammatory conditions such as rheumatoid arthritis.”
If you suspect you’re sensitive to nightshades, Sandon says, avoid eating them for two weeks. Then slowly add them back into your diet. Wait about three days between each treatment as reactions may be delayed. She recommends keeping a food and symptom diary to keep track of possible sensitivities.
read more: Magnesium supplements are a vibrant new aid for sleep and anxiety. Do they work?
Briana Butler, CEO of Gnaw Collective and a registered dietitian nutritionist specializing in nutrition coaching for athletes and women of color, explains that a registered dietitian can guide individuals through an elimination diet to identify food sensitivities and explore other potential factors, such as gut health. “In my opinion, there just isn’t enough research to just cut back on it [nightshades] completely,” she says. “These statements cannot possibly apply to everyone. It literally has to be taken on a case by case basis and figuring out, okay, what’s actually going on?
Butler points out that outright allergies to nightshades are rare because they are not among the top nine most common allergens. Both Sandon and Butler caution against eliminating nightshades without substantial evidence of personal sensitivity. They encourage consultation with healthcare professionals for those experiencing side effects to ensure that dietary changes are both necessary and beneficial.
The biggest takeaway? Our bodies respond to different foods in unique ways. While some people may need to avoid certain foods, labeling them as toxic to everyone misrepresents the complexity of human biochemistry, Schwarcz says. “The biggest problem here, as with so many such issues, is taking a kernel of truth and then extrapolating it.” He warns about the widespread spread of fear mongering on platforms like TikTok, where personal sensitivities are sometimes inflated into universal truths. Above all, most Americans don’t eat enough fruits and vegetables to begin with. Why limit your choices even further?
‘Some people can’t tolerate beans, eggplants or whatever. You don’t eat them. But you don’t go on TikTok and tell everyone in the world that this is poison,” he says. For example, Schwarcz is allergic to fish. But fish is healthy, and he will never tell you to stay away from it just because he does.