What Are Nightshades? Are They Bad for You?

When it comes to food and nutrition, it’s common for rumors about the benefits or harms of particular foods to be spread and exaggerated. Typically, these rumors are based on a small number of studies or an exaggeration of potential harm, often spread by a few loud voices. The truth about the health benefits of a food is typically not black and white.   

Nightshades, a family of plants that includes tomatoes and potatoes, have been seen as controversial because some people believe they might be harmful. But what is the truth about this family of vegetables, and do you need to avoid them? 

What Are Nightshades? 

Nightshades belong to a family of over 2000 plants known as Solanaceae. There are many common foods and spices that belong to this family. Nightshades include:

• Tomatoes 
• Eggplants 
• Bell peppers 
• Potatoes (except sweet potatoes)
• Tomatillos 
• Goji berries 
• Jalapenos 
• Pimentos 
• Cayenne 
• Paprika

Tobacco and Belladonna, a poisonous plant, are also part of the Solanaceae family.

Nightshades are a unique group of plants because they contain compounds called alkaloids, bitter substances the plants use to repel insects. These compounds are the primary reason for the controversy around nightshades. 

Nightshades: Helpful or Harmful?

The edible plants in the nightshade family are rich in many nutrients. Tomatoes, for example, are a source of lycopene, vitamin C, potassium, and more. Eggplants are a source of fiber, essential for regulating digestive health.  

Another nutritional benefit of nightshades is their antioxidant properties. Several nightshade vegetables, such as tomatoes and bell peppers, are rich in antioxidants which can help protect the body against oxidative stress caused by free radicals. For most people, these plants provide a hefty dose of nutrition and are an excellent addition to a healthy diet.

Some studies have found that alkaloids may contribute to inflammation of the digestive tract, which is what sparked the controversary around nightshades. The inflammation caused by alkaloids may trigger a condition called leaky gut, which has been linked to an increased risk of autoimmune diseases.

While some older animal studies did find a connection between inflammation and alkaloids, most of these studies used doses much higher than most people would consume in a normal diet. Additionally, more recent research has found that some alkaloids may have anti-inflammatory benefits for people with certain digestive conditions.

Nightshades can trigger an allergic reaction in some people. Symptoms may include hives, rashes, vomiting, or other digestive disturbances. You should not consume nightshades if you are allergic to them. 

Should You Eliminate Nightshades?

Nightshade vegetables are a healthy addition to a balanced diet and most people do not need to avoid them. In fact, limiting them may reduce the nutritional quality of your diet. Nightshades are nutrient-dense, low-calorie foods that are a good source of many important vitamins and minerals. Overall, they offer more potential health benefits than negative effects.

If you do struggle with an autoimmune or inflammatory condition, consider discussing your diet with a registered dietitian or healthcare provider before eliminating foods. Some people do report an improvement in symptoms when eliminating nightshades from their diet, but a professional should always supervise an elimination diet to ensure you are meeting your nutrient needs.

References:  

1. Cárdenas, P. D., Sonawane, P. D., Heinig, U., Bocobza, S. E., Burdman, S., & Aharoni, A. (2015). The bitter side of the nightshades: Genomics drives discovery in Solanaceae steroidal alkaloid metabolism. Phytochemistry, 113, 24–32. 

2. FoodData Central. (n.d.). Retrieved May 19, 2023, from https://fdc.nal.usda.gov/fdc-app.html#/food-details/1999634/nutrients 

3. Huang, D. (2018). Dietary Antioxidants and Health Promotion. Antioxidants (Basel, Switzerland), 7(1). https://doi.org/10.3390/antiox7010009 

4. Camilleri, M. (2019). Leaky gut: mechanisms, measurement and clinical implications in humans. Gut, 68(8), 1516–1526. 

5. Iablokov, V., Sydora, B. C., Foshaug, R., Meddings, J., Driedger, D., Churchill, T., & Fedorak, R. N. (2010). Naturally occurring glycoalkaloids in potatoes aggravate intestinal inflammation in two mouse models of inflammatory bowel disease. Digestive Diseases and Sciences, 55(11), 3078–3085. 

6. Bai, R., Yao, C., Zhong, Z., Ge, J., Bai, Z., Ye, X., Xie, T., & Xie, Y. (2021). Discovery of natural anti-inflammatory alkaloids: Potential leads for the drug discovery for the treatment of inflammation. European Journal of Medicinal Chemistry, 213, 113165. 

7. Eke Gungor, H., Uytun, S., Murat Sahiner, U., & Altuner Torun, Y. (2016). An unexpected cause of anaphylaxis: potato. European Annals of Allergy and Clinical Immunology, 48(4), 149–152.