4 Myths About Nightshade Vegetables

Some popular diets suggest avoiding eggplants, tomatoes, peppers and potatoes. They're wrong!

nightshade_vegetablesphoto credit: shutterstock

Sometimes even vegetables get a bad rap. Take the nightshade vegetables or Solanaceae, a plant family that includes eggplant, peppers, potatoes and tomatoes. (The term ‘nightshade’ may have been coined because some of these plants prefer to grow in shady areas, and some flower at night.) An online search of ‘nightshade vegetables’ yields results linking them to a host of health ailments from arthritis to migraines. Naturo­paths sometimes recommend that people with arthritis avoid nightshades. And Patricia J. Wales, a naturopathic doctor in Calgary, says naturopaths may suggest that people with osteoarthritis eliminate nightshades. These vegetables are also excluded from certain eating plans. Dr. Joshi’s Holistic Detox‘endorsed by Gwyneth Paltrow and Kate Moss’claims nightshades are related to poison ivy and potentially poisonous. ‘But poison ivy isn’t even in the same plant family,’ explains Barry Micallef, a plant biochemistry expert at the University of Guelph.

Why the bad reputation? Some people may think nightshade vegetables are harmful because they’re confusing them with ‘deadly nightshade‘ or Atrope belladonna, an inedible weed that’s also part of the Solanaceae family, explains Micallef. Historically, the deadly nightshade has been associated with witchcraft. When ingested in large amounts, it may cause convulsions or even death. But that has nothing to do with these vegetables. Here, we bust four other myths:

1. Do nightshades contribute to osteo­porosis?

Doubtful. Certain macrobiotic diets recommend that people with health challenges avoid nightshade vegetables and that even healthy people should eat them infrequently, says Judy MacKenney, a counsellor at the Kushi Institute, a macrobiotic edu­cational institute in Becket, Mass. ‘Nightshades are high in oxalic acid,’ she claims, ‘which inhibits the absorption of calcium, and can weaken bones and lead to osteoporosis.’ But Stephanie Atkinson, a member of the scientific advisory committee for Osteoporosis Canada, says that while oxalates are known to bind calcium in the intestine, reducing calcium absorption, this occurs only when calcium intakes are very low and oxalate intakes very high. Nightshades, however, are not high in oxalic acid, she says. ‘The alkali contributed by vege­tables and fruits is bene­ficial for bones as it protects them from using bone to neutralize blood acid.’

2. Do they all contain a toxic alkaloid?

No. Many alternative medi­cine websites allege that nightshade vegetables contain a toxic alkaloid compound called solanine, a defence mechanism in some Solanaceae plants that protects against natural threats such as insects. It’s true that solanine may develop in potatoes, which turn green when they are exposed to light during growth, says Micallef. (That’s why potatoes with green areas should be discarded.)

Contrary to the rumours, however, eggplant, peppers and tomatoes’even the green ones’do not produce solanine and are perfectly safe to eat, he says.

3. Do nightshade vegetables worsen arthritis pain?

Doubtful. Much of the online dis­cussion concerns nightshades and arthritis, and the notion that eating these vegetables causes an increase in pain or inflammation. But no scientific evidence supports that theory. ‘I’m not aware of any studies in peer-reviewed journals that prove or disprove that they affect arthritis,’ says arthritis expert Mark Erwin, an assistant professor of orthopedic surgery at the University of Toronto. ‘There are a lot of references to it, but the evidence is mostly anecdotal.’ There’s also no scientific reason to avoid nightshades even if you have arth­ritis, says Pamela Piotrowski, a registered dietitian at the Arthritis Society of Ontario. ‘Many people have food intolerances. If you start to feel achy every time you eat tomatoes, then maybe, for you, tomatoes are a contributing factor.’ But even if your symptoms disappear after eliminating tomatoes, it would be hard to pinpoint that as the cause since many factors can affect arthritis.

4. Do they cause migraines?

No. Linking nightshades to migraines is also without merit, according to Dr. Jonathan Gladstone, director of the Gladstone Headache Clinic and director of neurology at Cleveland Clinic Canada in Toronto. ‘I am certain that headache experts internationally would be in agreement that there is no evidence that tomatoes, peppers, eggplant and potatoes cause migraines,’ he says.

The health benefits of nightshades ‘far outweigh any risks,’ says Piotrowski. Tomatoes and peppers are amazing sources of antioxidants that lower the risk of cancer and heart disease; potatoes are high in vitamin C; and eggplant is a source of vitamin K. All are high in fibre. If you do want to elimin­ate them, make sure you get this nutritional value from other foods.

This article was originally titled “Four myths about ‘nightshade’ vegetables,” in the September 2009 issue of Best Health. Subscribe today to get the full Best Health experience’and never miss an issue!’and make sure to check out what’s new in the latest issue of Best Health.

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