White (not sweet) potatoes, tomatoes, sweet and hot peppers, eggplant, tomatillos, tamarios, pepinos, pimentos, paprika, cayenne, and Tabasco sauce are classified as nightshade foods. The ongoing question is, “Do nightshade vegetables increase joint problems such as arthritis?” The controversy stems from alkaloids, a particular compound found in nightshade foods. Whether alkaloids can contribute to joint damage is not clear from current levels of research. Some researchers have speculated that nightshade alkaloids can contribute to excessive loss of calcium from bone and excessive depositing of calcium in soft tissue. For this reason, these researchers have recommended elimination of nightshade foods from the meal plans of all individuals with osteoarthritis, rheumatoid arthritis, or other joint problems like gout.
“Nightshade” is actually the common name for more than 2,800 species of plants, herbs, shrubs, and trees, many with very different properties and constituents. Nightshades are actually more famous as drugs than as foods for example, mandrake, tobacco, and belladonna.