Nightshades are a fascinating and important plant family, with the Latin name Solanaceae.
Major nightshades that produce food are potatoes, tomatoes, peppers, and eggplants. Less common family members include goji berries, the pepino melon, ground cherries, and tomatillos. The increasingly popular herb ashwagandha (Withania somnifera)—also called Indian ginseng, poison gooseberry, or winter cherry—is also a nightshade.
Potatoes, tomatoes, peppers were all domesticated in Central and South America, along with another important nightshade: tobacco. When these nightshades moved to Europe and Asia they profoundly influenced both regional cuisines and agricultural economies, helping to shape the contours of the modern world as part of a phenomenon called the Columbian Exchange. It’s hard to find a contemporary cuisine where they aren’t heavily represented.
In addition to their prevalence in global cuisines, nightshades are also source materials for additives such as food starch and modified food starch (potato). They are commonly used colorants (paprika oleoresin). Nightshade peppers are also to source natural flavor molecules. Food companies are not required to disclose specific spices or flavors below a certain threshold. That means that if you are particularly sensitive to nightshades, a large number of items on grocery shelves are off limits.
The nightshade name comes from deadly nightshade, or belladonna, a poison known at least as far back as the classical Greeks. Like all plants, nightshades produce an amazing array of chemical compounds, including a family of chemicals called glycoalkaloids. These are thought to have evolved to discourage animals from nibbling. Other notable nightshade compounds include atropine (from mandrake, used as early as the fourth century BC) and scopolamine (from henbane, documented in the first century AD).
The nightshades that most of us eat every day also produce poisonous glycoalkaloids. Potatoes are monitored for levels of the alkaloids solanine and chaconine. For a long time we thought that these were related to the greening of potatoes, and that’s why you were advised to remove sprouts and any green peels from potatoes. Research has put that precaution in doubt, but it is clear that improper storage and handling can increase glycoalkaloid levels.
That doesn’t mean these plants are poisonous. All plants contain many things that, at a high enough dose, are poisonous. It’s the dose that makes the difference. Nicotine is the most notorious chemical of nightshade origin, and while it’s clearly recognized as a poison—it can kill you quickly, not just over decades—it’s also still regularly consumed as a stimulant. Too much scopolamine or atropine could kill you, a smaller dose may make you hallucinate, while smaller doses still may have medical benefit.
Click here for an extensive exploration of nightshade chemistry and how it might influence human health.