References and more info can be found at this link. Credit to The World's Healthiest Foods.
"You don't eat tomatoes!?" "What on earth can be wrong with a tomato?" These are the common reactions we get on the topic of nightshades. So let's dive in and look into exactly what nightshades are and why some of us might want to avoid them.
When it comes to food, nightshades are found in some fruits and vegetables. They are classified as nightshades because they contain alkaloids; which are a naturally occurring chemical compound. Alkaloids "can impact nerve-muscle function and digestive function in animals and humans, and may also be able to compromise joint function." The good news is not everybody is sensitive to nightshades and can tolerate the alkaloid content just fine. Others of us are not so fortunate and are pre-disposed to be sensitive to them. If excessive muscle soreness and joint pain are constant for you then removing nightshades from your diet are an easy way to see if you are sensitive to them. Sometimes avoiding them entirely will help alleviate associated symptoms.
"Nightshade vegetables and fruits"
The most famous food members of the nightshade family include potatoes (Solanum tuberosum), tomatoes (Lycopersicon esculentum), many species of sweet and hot peppers (all species of Capsicum, including Capsicum annum), and eggplant (Solanum melongena). Less well known, but equally genuine nightshade foods include ground cherries (all species of Physalis), tomatillos (Physallis ixocapra), garden huckleberry (Solanum melanocerasum), tamarillos (Cyphomandra betacea), pepinos (Solanum muricatum), and naranjillas (Solanum quitoense). Pimentos (also called pimientos) belong to the nightshade family, and usually come from the pepper plant Capsicum annum. Pimento cheese and pimento-stuffed olives are therefore examples of foods that should be classified as containing nightshade components. Although the sweet potato, whose scientific name is Ipomoea batatas, belongs to the same plant order as the nightshades (Polemoniales), it does not belong to the Solanaceae family found in this order, but to a different plant family called Convolvulaceae.
Nightshade spices
The seasoning paprika is also derived from Capsicum annum, the common red pepper, and the seasoning cayenne comes from another nightshade, Capsicum frutenscens. Tabasco sauce, which contains large amounts of Capsicum annum, should also be considered as a nightshade food. It may be helpful to note here that black pepper, which belongs to the Piperaceae family, is not a member of the nightshade foods."