To help set the record straight, we spoke with board-certified functional medicine physician Vincent Pedre, MD, “America’s Gut Doctor” and the author of The GutSMART Protocol, and Lauren Manaker, MS, RDN, LD, CLEC, CPT, a registered dietitian based in Charleston, to learn more about what the science says on nightshades and why there’s so much controversy regarding these seemingly unassuming dark-hued veggies.
To put it all out there, Dr. Pedre and Manaker shared insights into why some folks should, in fact, avoid nightshade vegetables. However, generally speaking, for the greater majority, consuming them is perfectly fine. (...As anticipated.) More ahead on what's to know about nightshade vegetables and how they can impact health.
What exactly are nightshade vegetables, and why do they get a bad rap?
Before we jump into the nitty gritty, it’s important to outline the main characteristics of nightshade vegetables. “Nightshades are a group of plants that make insect-repelling alkaloids that sometimes can have harmful effects on humans,” Dr. Pedre says. These plants can be broken into two categories: edible and inedible. “Plants in this category include edible plants like tomatoes, eggplant, peppers, and potatoes, as well as goji berries, huckleberries, ashwagandha—and herb often used for stress relief—and gooseberries. But inedible nightshade plants also exist; some of them are potentially deadly, like tobacco, belladonna, and mandrake.”
The reason why these types of plants are often looked at by nutritionists and doctors is due to the main alkaloid found in them, solanine. “If you eat too much of this alkaloid, it can make you feel sick with nausea, diarrhea, or even fever and headache. Nightshades may also cause acid reflux, indigestion, gas, bloating, and joint pain,” Dr. Pedre says. According to him, the highest concentration of this alkaloid is usually found in the skin of nightshade fruits and vegetables, and they’re even more prevalent when the plant’s still green or unripe.
In addition to alkaloids, the skins and seeds of nightshades contain lectins, which are proteins that bind to carbohydrates that science has shown may be of concern in high concentrations. "However, it’s extremely unlikely that a person will eat enough eggplant, for example, to equate to an amount of alkaloids or lectins that would be of concern," Manaker says.
"It’s extremely unlikely that a person will eat enough eggplant, for example, to equate to an amount of alkaloids or lectins that would be of concern."—Lauren Manaker, MS, RDN
How to tell if nightshade vegetables are suitable for you
Chances are, they are. While it’s important to decipher whether or not nightshade vegetables are safe for you on a case-by-case basis, both experts say that we shouldn't blindly cut out nightshades without negative side effects. They also share that the majority of folks won't experience any adverse side effects from eating nightshades (yes, despite their alkaloid and lectin content).
“The confusion around nightshades stems back to the fact that they may be okay for some people and lead to inflammation and pain in others,” Dr. Pedre says. “Typically, nightshades are contraindicated in people who have inflammatory, arthritic conditions—like osteoarthritis and rheumatoid arthritis—because they tend to aggravate the underlying disorder.”
That said, Dr. Pedre also notes that the scientific research is still inconclusive regarding whether (or not) nightshades are harmful even to patients with inflammatory conditions. “While the internet is drowning in claims that nightshades trigger an inflammatory response, the medical literature doesn't offer the same advice. It would be a shame to live without nightshade foods without any true clinical reason, especially since so many of these foods are packed with nutrients,” Manaker agrees. To further emphasize this point, some studies have indicated that anatabine—another plant alkaloid found in some nightshade vegetables—can even potentially reduce joint pain, stiffness, and improve functionality in patients with osteoarthritis or joint injury.
“While the internet is drowning in claims that nightshades trigger an inflammatory response, the medical literature doesn't offer the same advice. It would be a shame to live without nightshade foods without any true clinical reason, especially since so many of these foods are packed with nutrients."
According to Dr. Pedre, due to the limited research on nightshades, the best way to decipher whether or not nightshade vegetables are for you is by doing a bit of trial and error: “I encourage people to use a food log to find patterns in how certain foods affect their gut as well as their overall health to better individualize the best way to eat for their body type. In my clinical experience, removing nightshades from the diet has been reported by some of my patients over the years to improve their underlying inflammatory conditions. Therefore, a nightshade elimination diet should still be considered as a possible intervention in people with arthritic or inflammatory health issues. A four-week elimination can be followed by a reintroduction—one nightshade at a time every three days—to see if one of them triggers a worsening of symptoms,” Dr. Pedre says.
What are the potential health benefits of consuming nightshade vegetables?
It’s important to note that Dr. Pedre also believes that those without underlying illnesses and who maintain good gut health can typically reap the very positive benefits of nightshade vegetables as long as they aren’t consumed in high doses. “Nightshades are also rich in vitamins, minerals, and antioxidants, which can have all have health and gut benefits,” he says. For instance, eggplants are a good source of fiber, potassium, and vitamins B1, B6, and K. Meanwhile, purple potatoes are also rich in resistant starch, a great fiber source, and prebiotics for the gut microbiome.
“Many nightshade vegetables are a part of one of the healthiest diets on the planet—the Mediterranean diet—which often pairs them with anti-inflammatory omega-3s found in oily fish, like wild-caught salmon, or avocado, nuts, and of course, plenty of heart-healthy olive oil,” Dr. Pedre says.
What’s more, Manaker doesn’t want anything to stand in the way of folks getting enough veggies in their diets. “Unfortunately, with only 10 percent of Americans eating enough fruits and vegetables on a given day, anything that gets in the way of eating more produce unnecessarily is not something I am a fan of,” she says.
TL;DR? Here’s a case for eating nightshade vegetables if it’s appropriate for you.
An RD's in-depth guide to nightshades and lectins:
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