What Are Nightshade Vegetables, and Are They Bad for You? Here’s What the Science Says
Key takeaways:
Nightshade vegetables include potatoes, tomatoes, and eggplant. These vegetables are rich in nutrients and often recommended as staples of a nutritious diet.
Nightshades contain the alkaloid solanine, which is toxic in high concentrations. Potatoes that have turned green are most likely to cause solanine toxicity.
Some people say eliminating nightshades helps reduce arthritis pain and autoimmune disorder flare-ups.
You might have heard that some celebrities and athletes avoid nightshade vegetables — like tomatoes, bell peppers, and eggplant. But these vegetables are usually on lists of nutrient-rich foods. If dietitians and other healthcare professionals tell us to eat them in abundance, why would some diets advise against them?
Before cutting out nightshades, find out what the research says about these plants and why they’re controversial.
What are nightshade plants?
The nightshade family, Solanaceae, consists of more than 2,000 plants. They contain alkaloids, which are chemical compounds that contain nitrogen. They give plants a slightly bitter taste, which helps protect the plant from disease and insects.
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Nightshades are a diverse family. It includes plants ranging from potatoes to tobacco. While some nightshades are edible food, others are poisonous. This can make people more suspicious of edible nightshades like potatoes and bell peppers.
List of nightshade vegetables and fruits
Along with many other common fruits and vegetables, edible nightshades include:
Tomatoes
Potatoes (but not sweet potatoes)
Peppers, like bell peppers, jalapenos, and cayenne peppers
Eggplant
Tomatillos
Goji berries
In addition to the foods mentioned above, people who avoid nightshades also avoid sauces and spice blends that include peppers — like cayenne and paprika.
Are sweet potatoes nightshades?
Sweet potatoes are not nightshades. Even though sweet potatoes may seem similar to white potatoes, they actually belong to a completely different family of plants (called morning glories).
Health benefits of nightshade plants
The nightshade family has many health benefits. And many medications use derivatives from nightshades. For example, belladonna, a powerful ingredient that can help relax muscles, is derived from a nightshade.
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Nightshade vegetables are also rich in nutrients. Some common nightshades and their beneficial components are:
Tomatoes: a rich source of antioxidants, folate, potassium, and vitamins C and K
Potatoes: packed with fiber, potassium, and vitamins C and B6
Peppers: high in flavor but low in calories and packed with vitamins A and C, potassium, and folic acid.
Eggplant: a source of antioxidants, fiber, and manganese
Are nightshades bad for you?
Nightshade plants contain alkaloids. The alkaloids solanine and chaconine can be poisonous in high concentrations. This is most common with potato sprouts, green potato skins, tomato vines, and green tomatoes.
Affected potatoes will have a bitter taste, can be irritating to the gastrointestinal tract, and can cause stomach pains and diarrhea. But this reaction isn’t common — a person would have to consume a very large amount of affected potatoes to become seriously ill or die.
To avoid being exposed to potentially dangerous levels of these alkaloids, the best thing to do is to compost any potatoes or tomatoes that have turned green (or at least cut off the green part) and to not eat tomato stems. Cooking affected produce won’t reliably remove solanine.
Nightshades and arthritis
Much of the criticism around nightshade plants is linked to the belief that solanine causes inflammation. However, research doesn’t back up this claim. In fact, the Arthritis Foundation lists nightshades among the best vegetables for arthritis. And potatoes, tomatoes, eggplant, and peppers all have antioxidants that are considered anti-inflammatory.
But some people with arthritis report feeling better after eliminating some or all nightshades from their diet. It’s not clear why this happens, since nightshades don’t cause inflammation. One theory is that nightshades might increase inflammation in people already susceptible to it.
If you suspect nightshades are a problem for you, you can follow the steps to an elimination diet. The biggest risk in avoiding tomatoes, peppers, and potatoes is a nutrient deficiency. So be sure to substitute other nutrient-rich vegetables — like leafy greens, cauliflower, and sweet potatoes. And be sure to talk with your healthcare team about any diet changes you make, particularly if you’re being treated for a health condition.
Nightshades and solanine
Some people say that nightshade consumption leads to a buildup of solanine and the protein lectin in the body. They believe this buildup causes damage to the gut, inflammatory bowel disease, leaky gut, arthritis, Type 1 diabetes, allergies, and flare-ups of autoimmune conditions.
Research studies haven’t validated these claims for humans. But one study with mice showed that consumption of alkaloids in potato skins significantly increased inflammation of the intestines.
Solanine is also said to reduce calcium stores in the bones. And petri-dish studies of animal cells have shown that solanine can increase concentrations of calcium ions, which kick off the process of cell death. But, again, no studies with humans have mimicked these results.
Who should not eat nightshade vegetables?
Nightshade vegetables are considered safe for most people, although some people may have allergic reactions.
People who are allergic to any nightshade vegetable should avoid that nightshade. Symptoms of a food allergy typically occur within an hour of eating the food and include:
Skin rash or itching
Swollen lips or tongue
Itchy or sore throat, difficulty swallowing, or a swelling feeling in the throat
As mentioned above, some people may find that they have fewer autoimmune disease flare-ups or reduced arthritis pain when they avoid nightshades. If you find avoiding these foods helps you, you may want to cut back on nightshades to feel your best. But, again, stave off nutrient deficiencies by replacing nightshades with other nutritious foods.
The bottom line
Nightshade vegetables are a family of plants that include peppers, tomatoes, and potatoes. For most people, these are nutritious foods that provide health benefits. But some people with arthritis or autoimmune conditions prefer to avoid them. No scientific studies have shown that eliminating nightshades reduces arthritis pain or flare-ups of autoimmune conditions. But some people have seen improvement in their symptoms when they pass on these fruits and vegetables.
Why trust our experts?
References
Arthritis Foundation. (n.d.). Best vegetables for arthritis.
Cornell College of Agriculture and Life Sciences. (n.d.). Steroid alkaloids.
Gao, S., et al. (2006). Effect of solanine on the membrane potential of mitochondria in HepG2 cells and [Ca2+]i in the cells. World Journal of Gastroenterology.
Gebhardt, C. (2016). The historical role of species from the Solanaceae plant family in genetic research. Theoretical and Applied Genetics.
Iablokov, V., et al. (2010). Naturally occurring glycoalkaloids in potatoes aggravate intestinal inflammation in two mouse models of inflammatory bowel disease. Digestive Diseases and Sciences.
Jerzykiewicz, J. (2007). [Alkaloids of Solanaceae (nightshade plants)]. Advances in Biochemistry.
ScienceDirect. (n.d.). Solanine.
