Nightshade vegetables, including potatoes, tomatoes, peppers, and eggplants, are common foods with a lot of nutrients and serve as staple foods for various cultures. However, they have become a topic of debate among health providers. Some believe that they can trigger inflammation and immune dysfunction, leading some to advocate for a nightshade-free diet. This article reviews the health effects of nightshade vegetables to help you decide if these foods are right for you, using scientific evidence, expert opinions, and fact-checked information.
What are Nightshades?
Nightshade vegetables belong to the family of plants with the Latin name Solanaceae. The family Solanaceae variety extends well beyond vegetables to include innocuous flowers, such as morning glories, and even toxic herbs, such as Atropa belladonna. The origin of the name nightshades is unclear but could be related to their dark and mystical past. Some nightshades are rumored to have been formerly used as narcotics and hallucinogens.
The nightshade family contains over 2,000 varieties of plants, but very few of them are actually eaten as food. Some, such as belladonna, are even poisonous. However, nightshades also include vegetables that have been staple foods of many societies for hundreds of years.
Some of the most commonly consumed nightshade vegetables include:
- Eggplants
- Bell peppers
- Potatoes (but not sweet potatoes)
- Tomatillos
- Tomatoes
- Jalapeños and other chili peppers
- Pimientos
- Goji berries
Multiple herbs and spices are also derived from these vegetables, including cayenne pepper, crushed red pepper, chili powder, and paprika. Additionally, several condiments and other common food items contain nightshade vegetables as ingredients, such as hot sauce, ketchup, marinara sauce, and salsa.
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Although they’re generally referred to as vegetables, many nightshades are botanically considered fruits, such as tomatoes, eggplants, and peppers. Technically tomatoes are fruit, so nightshades include fruits as a result.
Nutritional Benefits of Nightshades
Many health professionals encourage you to eat nightshades because of their high nutrient density. Nightshade vegetables and fruits are also very high in nutrients. This means they pack a lot of nutrients with fewer calories.
- Tomatoes: Tomatoes are good sources of vitamins A and C. They also contain an antioxidant called lycopene. These nutrients may reduce markers of inflammation and lower the risk of several chronic diseases. Tomatoes are also one of the best sources of the phytonutrient lycopene. Your body can absorb more lycopene when the tomatoes are cooked, so eat a variety of tomato-based foods.
- Peppers: Peppers contain incredible amounts of vitamins A and C, plus potassium and folic acid. They also contain few calories but add tons of flavor. Vitamin C can provide many health benefits, including helping enhance iron absorption. Confused by colorful bell peppers? Green peppers typically have the most zip followed by red peppers, while yellow and orange are fairly mild. Raw, bell peppers are a good addition to salads or as a snack with hummus.
- Chili peppers: Chili peppers contain capsaicin, which gives the peppers their heat. Supplementing with capsaicin powder may help to alleviate heartburn symptoms and may benefit weight loss efforts by helping reduce calorie intake. Capsaicin is the active ingredient in hot peppers and is most commonly recognized for its anti-inflammatory properties, but it should also be noted that it is an alkaloid. Anyone who has eaten a ghost pepper or habanero can attest to the irritation they can ignite. Capsaicin’s irritant properties actually cause a release of substance P - a neuropeptide that plays a role in the communication of pain messages. After the initial irritation of contact with capsaicin and the release of substance P, there is a refractory period of deadened sensation.
- Eggplants: Eggplants are a source of dietary fiber, providing 2.5 grams of fiber per cup. This important nutrient helps regulate bowel movements and may lower your risk of heart disease. Eggplants also contain a high amount of antioxidants and special phytonutrients, including phenolic compounds such as nasunin. Some people find the texture of eggplant unpleasant or the flavor bland. If you are one of them, give eggplant a supporting role in meals; cut it up into bite-size pieces and add with other vegetables to soup or stir fry instead of highlighting it as the main ingredient.
- Potatoes: Potatoes with the skins on contain fair amounts of potassium, vitamin B6, and manganese. Potatoes can be baked or roasted with herbs and a drizzle of olive oil. Look for deep purple potatoes at specialty grocers for an extra dose of antioxidants.
However, unlike most nightshades, potatoes are a starchy vegetable. One medium potato contains around 37 grams of carbs. People with diabetes or others looking to lower their blood sugar may need to avoid eating too many potatoes.
Potential Risks: Alkaloids and Inflammation
Although nightshade vegetables are a rich source of nutrients, many people claim they’re harmful and should be avoided. Nightshades contain chemical compounds called alkaloids, which contain nitrogen. The majority of these claims seem to center around a group of substances found in nightshades called alkaloids. Alkaloids are nitrogen-containing substances typically found in the leaves and stems of nightshades. They’re often very bitter and function as a natural insect repellent. But the edible portions of these plants contain some alkaloids, too. Consequently, many people with autoimmune diseases eliminate nightshades from their diets, believing they contribute to their health problems.
Most often, alkaloids are identified molecularly by a ring with a nitrogen atom and are derived from amino acids, though there are exceptions to this structure. Alkaloids are known for being the strongest, riskiest components in herbal medicine.
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Types of Alkaloids in Nightshades
- Solanine: Solanine is a type of steroid alkaloid known as a glycoalkaloid - an alkaloid merged with a sugar. When the body begins to metabolize solanine, the sugar separates and solanidine is left. Both steroid alkaloids are produced similarly to chlorophyll, which means there will be more concentrated amounts of them in the green portions of the plant. Solanine and the other nightshade steroidal alkaloids can irritate the gastrointestinal system and act as acetylcholinesterase inhibitors - affecting neurotransmitters.
- Capsaicin: Capsaicin is the active ingredient in hot peppers and is most commonly recognized for its anti-inflammatory properties, but it should also be noted that it is an alkaloid.
- Nicotine: Nicotine is an alkaloid substance in the tobacco plant, which happens to be a nightshade. Keep in mind that nightshades include quite deadly plants as well as generally safe vegetables.
Nightshades and Autoimmune Diseases
Research has yet to show that nightshade vegetables contribute to autoimmune diseases. However, some believe that certain groups of people may be better off eliminating nightshades. They claim that harmful substances found in these vegetables may contribute to inflammatory bowel disease and other autoimmune conditions.
Inflammatory Bowel Disease (IBD): IBD is a group of autoimmune diseases characterized by inflammation of the digestive tract. Examples are Crohn’s disease and ulcerative colitis. In people with IBD, the protective lining of the intestine doesn’t function properly and allows bacteria and other harmful substances to enter the bloodstream. This is sometimes called increased intestinal permeability, or “leaky gut”. When this happens, the body’s immune system attacks the harmful substances, leading to further inflammation of the gut and many adverse gastrointestinal symptoms, such as pain, diarrhea, and malabsorption.
While research on this is limited, a few studies in animals suggest that the alkaloids in nightshades may further aggravate the intestinal lining of people with IBD. In an older study on mice with IBD, the alkaloids in potatoes were found to adversely affect intestinal permeability and increase intestinal inflammation. It’s important to note that the alkaloids in these studies were in far higher concentrations than the amount found in a normal serving. This limited research in animals and test tubes suggests that people with IBD may benefit from eliminating or reducing nightshades. But research is needed in humans before more definitive recommendations can be made.
Effects on Other Autoimmune Diseases: Even less is known about the effects of nightshades on other autoimmune diseases. However, there may be some connection between increased intestinal permeability, or leaky gut, and autoimmune conditions like celiac disease, multiple sclerosis, and rheumatoid arthritis. Some experts believe that leaky gut could contribute to higher levels of inflammation all over the body that worsen disease symptoms. Based on this belief, some have suggested that nightshades may increase intestinal permeability and aggravate the symptoms of these autoimmune conditions, as well. Many people with these diseases have eliminated nightshades from their diets and report improvement in symptoms, but evidence for this recommendation right now is mainly anecdotal and needs to be studied.
Nightshade Sensitivities and Allergies
Other groups of people without autoimmune conditions claim that eliminating nightshades has dramatically improved their health. These people are often said to have sensitivities to nightshades. One of these groups includes people with arthritis, as some claim that eliminating nightshades provides pain relief. There’s an older theory that nightshades contain a form of vitamin D that causes calcium deposits that may contribute to joint pain and other arthritis symptoms. However, there doesn’t appear to be evidence that nightshades contain vitamin D or that eating these vegetables causes calcium deposits, arthritis symptoms, or other related health problems in humans.
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In addition to nightshade sensitivities, in rare cases, some people have allergies to specific nightshade vegetables. Symptoms of an allergy vary but can include skin rashes, hives, itching in the throat, swelling, and difficulty breathing. If you experience any of these symptoms when you eat a particular nightshade vegetable, it would be wise to stop eating that particular food and seek medical advice for further testing.
Determining if Nightshades are Problematic for You
Clearly, nightshade vegetables are not universally dangerous. Many of them have strong health benefits to offer the body. There is no conclusive research that draws the link between nightshade consumption and increased inflammation. Nightshade vegetables are healthy and harmless for most people. However, some people report reactions to consuming these foods, including joint pain, digestive discomfort, and reddening of the skin.
If you’re healthy and don’t have adverse reactions to nightshades, there’s no compelling reason to avoid them. They’re rich in nutrients and offer several potential health benefits. However, if you have an autoimmune condition like IBD or think you may be sensitive to nightshades, it’s best to work with a registered dietitian or other health professional to evaluate changes in symptoms through an elimination diet.
The Elimination Diet
If you suspect you may be sensitive to nightshades, don’t eat them for two weeks. Then slowly introduce them back into your diet. Allow about three days between each one.
If you decide to do this yourself, you would completely eliminate all nightshades and products containing these vegetables for at least 4 weeks. Be sure to keep track of the severity of your symptoms during this time. After this elimination period, you should start reintroducing nightshade vegetables one at a time back into your diet. Don’t make any other lifestyle changes during this time.
After reintroducing nightshades, compare the severity of your symptoms during your elimination and reintroduction periods. If symptoms were better during elimination and got worse when you reintroduced nightshades, you may want to continue to avoid eating them long-term. If symptoms weren’t different between the two periods, you should seek other treatments for your symptoms and continue eating nightshades.
Alternatives to Nightshades
If you decide to eliminate nightshades long-term, you’ll be missing out on the nutrients they provide. However, there are plenty of other foods to choose from that provide many of the same nutrients and health benefits.
Here are a few changes you can make to eat healthy while avoiding nightshades:
- Switch to sweet potatoes: Switching from white potatoes to sweet potatoes will help you avoid nightshades and provide much more vitamin A.
- Use pesto: Instead of tomato sauce in pizza and pasta, green pesto is a delicious alternative that should not contain nightshades. Red pesto usually contains tomatoes and should be avoided if trying to eliminate nightshades. Beets can also be used to make a “no-mato” sauce.
- Consume citrus fruits: Many nightshades contain vitamin C, but citrus fruits like oranges, tangerines, and grapefruits are also excellent sources.
- Eat more leafy greens: Leafy green vegetables like spinach, kale, and collard greens are great sources of many vitamins, minerals, and dietary fiber.
- Use Italian spices: Instead of cayenne or paprika, use Italian spices like basil, thyme, and rosemary.
Minimizing Alkaloid Content
If you still want to eat nightshades but would like to lower their alkaloid content, there are a few things you can try:
- Peel potatoes: In potatoes, the highest concentration of alkaloids is in the skin. One study showed that skinning potatoes before cooking removed up to 70% of the alkaloids.
- Bake potatoes: Baking potatoes in the oven may lower the alkaloid content more than boiling or steaming.
- Store potatoes properly: Store potatoes in a dark, cool place to prevent them from producing more alkaloids before you eat them.
- Avoid green tomatoes: Tomatoes contain more alkaloids in the stem and vine than in the fruit. Studies show that as tomatoes mature, the amount of alkaloids in the part that you eat decreases. So, it is unlikely to eat too many alkaloids from tomatoes, especially if you avoid unripe, green tomatoes.
- Fully cook nightshade vegetables: Since there are several different nightshade fruits and vegetables, there are multitudes of ways to cook them.