“What is your opinion on nightshade veggies?”
—“Organic Size Me”
Potatoes, tomatoes, tomatillos, chile peppers, and eggplants (as well as tobacco, petunias, cape gooseberries, and goji berries) are all members of the botanical family Solanceae, aka the nightshades. Many people think the consumption of nightshades contributes to numerous illnesses and conditions, including rheumatoid arthritis, osteoarthritis, chronic joint pain, swelling and/or stiffness, fatigue, malabsorption of calcium, depression, “leaky gut,” migraines, spina bifida and other birth defects, appendicitis, and hangnails. (Okay, I made that last one up.)
Scads of anecdotal evidence aside—I have no doubt that any number of people are sensitive or allergic to one or more nightshades—I’m still trying to dig up actual scientific data to buttress those claims. Dr. Joshi’s Holistic Detox, a diet book endorsed by movie stars and supermodels, does not count.
Of course, you probably already know that the plant family’s common name comes from its most (in)famous member, deadly nightshade (Atropa belladonna). Its hallucinogenic properties gave medieval witches the feeling they were flying, and murderous types have used it with great success for centuries. Still, it’s important to remember that, in the words of pioneering forensic toxicologist Alfred Swaine Taylor (1806–1880), “A poison in a small dose is a medicine.” Belladonna has long been an herbal pain reliever, muscle relaxer, and anti-inflammatory. Today, one of the primary uses for the drug atropine, derived from the plant’s roots, is in ophthalmology, in which it’s applied to the eye to dilate the pupil. It’s also used during surgery to maintain proper heart function, and is helpful in controlling gastric conditions such as colitis and diverticulitis.
Belladonna’s potency comes from a high content of atropine, scopolamine, and hyoscyamine. Those are all alkaloids, a type of naturally occurring nitrogenous chemical compound, and, according to the 1996 book Plant Alkaloids: A Guide To Their Discovery and Distribution by Robert F. Raffauf, more than 10,000 different ones have been discovered in species from more than 300 plant families. Part of the plants’ chemical arsenal to deter insects (hey, it’s not all about us), they are particularly common in the nightshades.
Take, for instance, the alkaloid capsaicin, present in the seeds and especially the placenta (where the seeds are attached to the flesh), of chiles. Although capsaicin activates the pain and heat receptors in our mouths, we can’t seem to get enough (cue John Mellencamp’s “It Hurts So Good”). First domesticated in South America, chiles both hot and sweet have become fundamental building blocks in cuisines around the globe.
Tomatoes and potatoes, two more nightshades that originated in South America, have also profoundly reshaped the world’s foodways (can you imagine Italian food without tomatoes?), not to mention its economics. And, in the form of the nutrient-dense potato, Solanceae had a significant effect on the political stability of much of Europe (it literally nourished nations and boosted population growth), and then mass emigration from Ireland to the United States during the Irish Potato Famine of 1845–1852.
Potatoes contain the most controversial alkaloid, solanine, which can, in large amounts, cause digestive upsets and in even larger amounts (more than anyone could eat at one sitting), paralysis, coma, and death. Although it’s a significant toxin, health guru Andrew Weil writes, “There hasn't been a single case of solanine poisoning due to eating potatoes in the United States for more than 50 years.” That’s because the modern potato varieties don’t produce much of it, and what there is, is concentrated in the green leaves and fruit (which looks like a green cherry tomato)—not in the underground tuber. If a tuber does have a greenish tinge or green spots on the skin, the color is harmless (it comes from chlorophyll), but it signifies the presence of an elevated solanine content due to exposure to light or either very hot or cold temperatures and should be avoided.
Even despite the effects the chemical compound has, it has a low oral toxicity. Andrew Montario, at Cornell University, writes, “First solanine levels in the blood are low after ingestion due to poor absorption by the gastrointestional tract. Second, it is removed from the body fairly rapidly in both the urine and the feces, usually within 12 hours, preventing accumulation in the tissues. Third, intestinal bacteria aids in the detoxification by hydrolyzing the glycoside into solanidine, which is less toxic than solanine and also poorly absorbed.”
And, interestingly, even though the party line has been that solanine is also a toxin in tomatoes, particularly in the leaves of the plant, recent research on plant compounds proves that not to be true. On July 28, 2009, food scientist Harold McGee reported in The New York Times that the alkaloid is actually tomatine, “a relatively benign alkaloid” and references Toxic Plants of North America, by George E. Burrows and Ronald J. Tyrl and published in 2001. A toxic dose of tomatine for an adult human would require at least one pound of tomato leaves, the authors conclude, and “the hazard in most situations is low.”
The bottom line? People with all types of arthritis are often told to avoid nightshades because they trigger inflammation, but unless you have a sensitivity or allergy to solanine or another chemical compound in the plants, then it seems a real shame to cut them out of your diet completely—they are chockfull of antioxidants and other good things.
The capsaicin in chiles, for example, is a strong anti-inflammatory and natural antibacterial agent. Green and yellow chiles are rich in the carotenoid lutein, essential to eye health, and mature red chiles are not only among the richest sources of carotenoids, but are high in beta-carotene and vitamin C. Tomatoes, a valued component of the Mediterranean Diet, contain lots of carotenoids, too—in particular, lycopene. Potatoes are a great source of vitamins, minerals, protein, and complex carbohydrates. And we haven’t even talked about eggplant, which boasts an antioxidant compound called chlorogenic acid, which fights free radicals; it also lowers LDL (bad) cholesterol and is antimutagenic, which means it can protect cells from mutating into cancer cells. Made in the shade.