What to Know About Nightshade Vegetables

Medically Reviewed by Kathleen M. Zelman, RD, LD, MPH on May 02, 2023
4 min read

Nightshade is a family of plants that includes tomatoes, eggplant, potatoes, and peppers. Tobacco is also in the nightshade family. Nightshades are unique because they contain small amounts of alkaloids.

Alkaloids are chemicals that are mainly found in plants. For something to be considered an alkaloid, it must contain nitrogen and affect the human body, usually from a medicinal perspective. Morphine and quinine are two examples of plant-based medicines that contain alkaloids.

Tomatoes are often thought of as being in the vegetable family due to their savory flavor, but they are actually a fruit. Fruit is an edible part of a plant that develops from a flower and contains seeds. Peppers and eggplant are also technically nightshade fruits. 

Vegetables are any other edible part of a plant, like the roots, stems, or leaves. Potatoes are a nightshade vegetable, not a fruit. 

While some alkaloids have positive effects on human health, others can affect them negatively. For example, the chemicals found in tobacco, a nightshade plant, can cause cancer.

The alkaloid found in nightshades is solanine. It functions as an insecticide while the plant is growing.

Eating too much solanine can make you feel bad. When potatoes turn green, they have more alkaloids in them, and they taste more bitter. That is why people usually recommend throwing out green and/or sprouting potatoes. If you eat green potatoes, you may get sick to your stomach with nausea or diarrhea. You can also get a fever or headache.

Normally, potatoes and other nightshade vegetables have an acceptable amount of alkaloids in them. You may feel some effects if you eat between two to five milligrams of solanine per kilogram of body weight. If you weigh around 150 pounds (68 kilograms) you would need to consume a minimum of 136 milligrams of solanine to feel ill.

For context, one eggplant has about 11 milligrams of solanine.

Studies show that potatoes can contain anywhere from 25-275 micrograms of alkaloids. The amount depends on the type of potato and where it was grown.

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.

Overall, there is no hard evidence that nightshade vegetables are bad for your health. Some preliminary research shows these vegetables may not be the best for people with certain inflammatory and auto-immune conditions like arthritis or inflammatory bowel disease. However, nightshades don't cause inflammation directly. They may increase inflammation that is already there.

How do you know if nightshades are bad for you? Experts recommend eliminating them from your diet for a few weeks. Then, reintroduce them and see how you feel. If you feel worse after reintroduction, you may have a sensitivity to nightshades.

Whether or not there is any conclusive evidence about nightshades and inflammation, you should never eat any foods that make you feel bad, or that worsen any conditions you have.

Other nutrients in nightshades may be good for your health. They contain antioxidants that protect cells from damage due to stress.

For example, anthocyanin, the antioxidant that gives eggplant its purple color, can reduce the risk of developing cancer, diabetes, and infections.

The antioxidant lycopene, found in tomatoes, may decrease the risk of some types of cancer and heart disease.

Nightshades also contain vitamins and minerals that contribute to good health, like Vitamin A and Vitamin C. Eating one bell pepper, for example, gives you your daily allotment of Vitamin C.

If you're concerned about high alkaloid content in nightshade vegetables but still want to benefit from including them in your diet, there are a few things you can try:

  • 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.
  • Baking potatoes in the oven may lower the alkaloid content more than boiling or steaming.
  • Store potatoes in a dark, cool place to prevent them from producing more alkaloids before you eat them.

Since there are several different nightshade fruits and vegetables, there are multitudes of ways to cook them. If you want to learn how to cook nightshades, popular dishes that usually contain them include:

  • Salsa
  • Bruschetta
  • Tomato soup
  • Gazpacho
  • Pasta with tomato sauce
  • Baked potatoes
  • French fries
  • Mashed potatoes
  • Potato salad
  • Hash browns
  • Scalloped potatoes
  • Stuffed bell peppers
  • Baba ghanoush
  • Eggplant parmesan