I have recently been asked why I recommend that many people should avoid or minimize nightshade vegetables in their diet. The main nightshade plants we use are potato, tomato, eggplant and bell and hot peppers (and tobacco). Nightshades refer to a group of plants that supposedly do their growth at night but may also refer to the narcotic qualities that these “Solanum” plants have, tobacco being in the same family. The main toxic substances found in nightshades are solanine, glycoalkaloids and alkamines. The greenish color found on many potatoes indicated solanine which is a toxin that is linked to rashes and other skin diseases. Glycoalkaloids cause red blood cells to self-destruct in vitro and alkamines contribute to nervous disorders. These substances have been linked with kidney stones, calcium depletion, nausea, abdominal pain and swelling, loss of red blood cells, ulcers, jaundice, rashes, muscle wasting, breathing difficulties, trembling, drowsiness and paralysis and is most famously connected to rheumatoid arthritis. Being expansive or yin in nature they make on crave animal products, especially dairy and red meat.
Nightshades have an interesting history, they were discovered being used by the Incas in Peru by the Spanish conquistadors in 1530. They had an elaborate process in preparing the peanut sized potatoes before they were considered edible. They would soak them in water the freeze them in the cold mountain air. Then they dried them in the sun and rubbed off the skin by waling on them barefoot until they turned black and hard as stones. They then soaked them for three to four day before being cooked in soups or ground into flour to make bread. Even today in Italy red peppers are often salted, burnt to a back crisp, the skins and seed removed and then cooked further before being considered edible!
During the 1600s and 1700s nightshades were grown ornamentally but not considered edible. The French thought they caused leprosy. Many in Europe thought potatoes caused hydrocephalus and general stupidity among those who ate them and their offspring. The tomato didn’t find its place in American kitchens until World War 1, before that they were believed to cause stomach cancer and appendicitis.
Some have suggested that the following groups of people avoid nightshades: people with arthritis, those on a macrobiotic diet, children with eczema, those with gastric reflux, those quitting smoking (nicotine and solanine are related), those of blood type A and B (which is half the population) and those with cystitis, lupus and psoriasis.
In the book, Energetics of Food by Steve Gagne there is a caution not just about the physical effects of nightshades but their energetic effect on emotions, mental attitude and character. Of the potato he says “It can contribute to mental symptoms of fatigue and drowsiness, scattered thinking, inability to pay attention, mental dullness, simplemindedness, blind allegiance and blind faith, as well as devotion to religious dogma and an overall dull spirit with a lack of creative thinking.” (Boy do Americans love their potatoes and French fries!)
There are some medicinal uses for nightshades however. Potatoes are supportive for conditions of tension accompanied by excess heat and dryness and can help reduce the sodium in tissues of those who have overdone salt. Tomatoes can reduce excessive fat accumulation in the body and can cool an over-heated metabolism and can calm and clear excess heat from the liver. Eggplants can help constipation and assist in reduction of abdominal swelling. It can also help balance fatty foods, especially cheeses, by thinning the blood. Peppers can stimulate appetite and digestion, and promote urination.